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Module 13

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Aircraft aerodynamics, structures and systems

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Table of contents

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13.01 Theory of flight 13.02 Structure 13.03 Autoflight 13.04 Communication and navigation 13.05 Electrical power 13.06 Equipment and furnishings 13.07 Flight controls 13.08 Instrument systems 13.09 Lights 13.10 On board maintenance systems 13.11 Air conditioning and cabin pressurization

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Table of contents

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13.12 Fire protection 13.13 Fuel system 13.14 Hydraulic power 13.15 Ice and rain protectiion 13.16 Landing gear 13.17 Oxygen 13.18 Pneumativ and vacuum 13.19 Water and waste 13.20 Integrated Modular Avionic (IMA) 13.21 Cabin systems 13.22 Information system

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Chapter 13,1

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THEORY OF FLIGHT

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Aircraft movements and flight controls

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The primary control surfaces on the longitudinal axis are the ailerons. They are moved by the lateral displacement of the control stick. Ailerons act in opposite directions while one aileron goes up, the other aileron goes down. If the pilot turns the control bar to the right, the right aileron moves up, while the left aileron moves down. In this way the ailerons change the camber of the wings, creating a variation of the produced lift

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Ailerons

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Ailerons

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Stabilizer: stabilize the airplane attitude Elevator: balance the airplane nose up/down habit

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Stabilizer / elevator

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When a rotation is imposed, one wing speeds up while the other slows down. The change in speed causes a change also in the lift on the two wings generating a roll movement (secondary effect) called yaw roll coupling.

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Vertical tailplane

Fin: fixed surface, provides directional stability to the airplane around the yaw axis Rudder: mobile surface, provides the yaw movement (ie. If the pilot push the left pedal the aircraft perform a yaw to the right) Yaw is the primary effect of rudder deflection.

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High lift devices are movable mechanism connected to the wings of many aircraft. The high lift devices are mainly used during the takeoff and the landing, to decrease the aircraft stalling speed. The flaps modify the air circulation around the airfoil, while the slats create the “slot”. The slot has the function to reinforce the boundary layer on the wing upper camber.

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High lift devices:slot, slat and flaps

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The spoilers are adjustable surfaces, hinged on the upper part of the wing, that have the task to interrupt the flow producing the lift. On many aircraft, spoilers have three functions, but they always decrease lift and increase drag The main type of spoilers is the ground spoiler. The ground spoilers dump the lift when the aircraft is on ground during the landing phase

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Drag inducing devices: spoilers, lift dampers, speed brakes

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Mach number and critical Mach number

The flight speed is often expressed as Mach number. The Mach number (M) is defined as the ratio of the speed of a body (V) to the speed of sound (c) in that air mass

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It is important to underline that the Mach number is a dimensionless parameter. The speed of sound is influenced only by the temperature and so by the flight altitude

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Swept-wing

On swept-wing aircraft, the wing section will be characterized by a smaller ratio between thickness and chord

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Variable geometry wings

Variable geometry wings, have the possibility to change their swept, during the mission, according to their flight speed.

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In this way, the aircraft can maintain stretched wings at low speeds, with a small swept angle, then to move them towards the fuselage, increasing the swept angle, at transonic and supersonic flight regimes

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It is important to underline that the aircraft isn’t leaded to the superstall attitude by incorrect actions on flight controls, but it reaches this condition by itself, further to aero-dynamics phenomena that happens. The tendency of a swept wing to present the superstall can be reduced by particular devices, such as the vortex generators, that are installed on the wing area.

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Module 13 – Aircraft aerodynamics, structures and systems

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Superstall

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The helicopter: Theory of flight

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A conventional helicopter is equipped with two rotors having different specific purposes. The first rotor at vertical axis is the main one and has a big diameter, this rotor provides the sustentation and permits the translated flight. The tail rotor at horizontal axis is the second one and has a smaller diameter, this rotor allows to equilibrate the reaction torque of the main rotor and to directionally control the helicopter.

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The helicopter: Theory of flight

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The rotors are made of a shaft, a hub and some blades connected to it. The hub is the central part and is generally composed of some ball bearings to permit the rotation of the element assembled on it. The hub is installed on the shaft.

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The shaft is the element that transmits the rotational motion. It can freely spin or be actuated by an engine. One or more blades are attached on the hub: they are the lift surfaces of the helicopter

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The helicopter: Theory of flight

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The helicopter: Theory of flight

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Rotors can be generally divided into 3 principal categories, according to the number of hinges in the hub: • Rigid rotors have only one hinge, which permits the rotation of the blade around its longitudinal axis. This hinge is called pitch hinge. When it turns the blade around this pitch hinge, the angle of attack of airfoil along the same blade varies, increasing or decreasing in relation with the imposed rotation. • Semi-rigid rotors have two hinges: the pitch hinge and the flapping hinge. The flapping hinge permits the blade rotation in the vertical plane. • In articulated rotors 3 types of hinges are present: the pitch hinge, the flapping hinge and the lead-lag hinge (or drag hinge). The drag hinge permits the blade movement in the plane of rotor rotation. 18.01.2017

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Autorotation is the descent of the helicopter with the power off. Air flowing upwards through the main rotor blades causes them to rotate in their normal direction. Pilot will control helicopter's rather fast rate of descent and use blade's stored up kinetic energy to, just before touch-down, apply collective and flare out to a gentle touchdown

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The helicopter: autorotation

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The vortex ring state (VRS), also known as settling with power, is a hazardous condition for a helicopter in flight. This occurs when the helicopter is descending with a rate of descent equal to the value of the speed induced by the rotor To come out by the vortex ring state, it is necessary to move the helicopter in straight flight, and to reduce the collective pitch

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The helicopter: vortex ring state

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Chapter 13,2

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Module 13 – Aircraft aerodynamics, structures and systems

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STRUCTURE – GENERAL CONCEPTS

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Foundamentals of structural systems

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The design concepts, used to project and to construct aircraft structures and components, can be classified in three categories: 1. • The fail safe concept 2. • The safe life concept 3. • The damage tolerance concept

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Fail safe concept • The fail safe criterion sets that the structure shall be able to have a certain residual strength, even if the failure of a component happens. • If an element is damaged other structural members must support the load of the failed component

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The landing gear of an airplane is made of a series of components, the element that absorbs the energy during the tuch down is the shock absorber. The landing gear of airplanes and helicopters has the scope to support the weight of the structure, when the aircraft isn’t in flight, but it is on ground.

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Landing gears of airplanes and helicopters

The choice about the typology of landing gear, which must be installed on airplanes and helicopters, is function of the type and of the main employ of the machine.

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Regarding the landing gears with wheels, the most basic configuration is the tricycle landing gear: fore try-cycle (the most common) and rear try-cycle

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Landing gears of airplanes and helicopters

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The landing gear of an airplane is made of a series of components: • The shock absorber • The brake • The wheel • The tire • The torque link (is a typical element of landing gear with wheels) • Some possible devices of extraction and retraction

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Landing gears of airplanes and helicopters

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Fundamentals of structural systems: regulations

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Airworthiness The airworthiness certifies the ability of an aircraft to fly. Airworthiness refers to the status of an aircraft, which is congruent with the approved standards, modified according to specifications approved by the authority or which is in accordance with the mandatory maintenance and has no inadequate parts installed. All these conditions are mandatory. The certificate of airworthiness attests that, in a specific moment, the aircraft has been checked and declared able to fly by an assigned subject. An aircraft with an expired certificate must not fly.

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Zonal and station identification systems

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In the frame location system the main manufacturer’s reference system includes 3 principal coordinates: 1. Station line: reference point near the aircraft nose 2. Buttock line or butt line: reference point on the longitudinal axis 3. Water line: reference line near the lower part of the fuselage

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Electrical bonding

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The bonding is the electrical connection of two or more conducting objects. • The main aim of the bonding is that to eliminate the potential differences among different points of the structure, making it at the same potential • Moreover, all electrical systems, present on board of an aircraft, must be adequately ground connected, with the aims: 1. To protect aircraft and personnel from hazards of lighting discharge 2. To protect personnel from shock hazards 3. To prevent the development of potential radio interferences

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Chapter 13,3

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AUTOFLIGHT

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Flight Director and FCC

A fundamental component of the autopilot system is the Flight Director (FD), which is generally connected to the Flight Control Computer (FCC).

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The FCC has the function to examine the aircraft position and the aircraft orientation.

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AHRS and CDU

The Attitude Heading Reference System (AHRS) is made of a series of 3-axis sensors that provide information about the heading, the attitude and the yaw of the aircraft, measuring the attitude, the angular and linear movements A modern AHRS is a strap-down system that exploits solid state gyros and accelerometers. A strap down system is a system in which the sensors are in agreement with the aircraft axes without the presence of hinges Other input data to the autopilot system can be inserted in a manual way directly by the pilot, through the Control Display Unit (CDU).

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The primary flight controls are operated through Power Control Unit (PCU), utilizing the hydraulic power to activate the electrohydraulic actuators. It is possible to design these units so that they respond to signals of the AFCS.

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The PCU includes an external input link and an internal control valve (called servo-valve) which directs hydraulic pressure to drive the actuator. The mechanical input is sent to the PCU from the pilot control through rods and cables, and, in modern installation, through the Fly-By-Wire (FBW) system electrical signals. The input link positions the control valve which directs pressure to the main piston to give the powered output.

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PCU

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AFCS classification

A system is called fail-passive (or fail-soft), when it is able to withstand a malfunctioning, without endangering passenger safety and without producing excessive deviations from the flight path.

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A system is called fail-active (or fail-operational), if its malfunctioning doesn’t reduce the total functionality of the system. In a fail-active system a failure can occur, but it leaves the entire

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system still working, without degrading its performances.

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Roll channel, pitch channel and yaw channel

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Roll channel • The roll channel, connected to ailerons of the aircraft, controls the movement around the longitudinal axis

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Pitch channel • The pitch channel, connected to elevator of the aircraft, controls the movement around the lateral axis, analyzing the commands that are generated by the FCC (Flight Control Computer) and that determines when and how the elevator will be moved

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Yaw channel • The yaw channel, connected to rudder of the aircraft, controls the movement around the vertical axis. • The yaw channel, connected to the rudder, receives two signals that determine when and how much the rudder will be moved. Autopilot control in the yaw axis and is not required in many small aircraft.

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The auto throttle system is an electronic circuit that controls the engine thrust within engine design parameters The auto throttle system is independent to the autopilot system, but it is typically coupled with it Basically, the auto throttle system mainly controls the RPM (Rate Per Minute), the fuel consumption of the engine, and the EPR (Engine Pressure Ratio).

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Auto throttle systems

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Thrust mode – speed mode

In the THRUST mode, the engine is maintained at a fixed power setting according to the different flight phases. For example, during the take-off, the auto throttle maintains a constant take-off power until take-off phase is finished

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In the SPEED mode the throttle is positioned in order to reach a set speed. This mode controls aircraft speed within safe operating margins. For example, if the pilot selects a speed which is slower than stalling speed, or a speed faster than maximum speed, the auto throttle will maintain a speed closest to the set speed that is within the safe range of speeds

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Automatic landing systems

The modern autopilot systems are also able to manage fully the landing procedure, in completely automatic way. To do this, they utilize the signals of the Instrument Landing System (ILS).

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In the case in which the system isn’t able to couple the ILS signal, the pilot will see the warning “Autoland fault”.

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If the auto-land system notices some data inconsistencies, an indicator will signal to pilot the writing “Approach only”, informing him about the impossibility to do the auto-land.

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Helicopter autopilot

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The autopilot systems for the helicopters are different from those of the airplanes, because the commands, that permit the flight conduct, are different • According to the number of commands, which the system is able to control and to manage, it can have: Tri-channel systems, with 3 control channels (channel of lateral cyclic, channel of longitudinal cyclic and channel of the rudder bar) Quadri-channel systems, with 4 control channels (channel of lateral cyclic, channel of longitudinal cyclic, channel of the rudder bar and collective pitch channel).

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The Stability Augmentation Systems (SASs) can operate in coupling with the Flight Director system.

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The SASs increase the stability and the maneuverability of the helicopter in presence of wind and turbolence and maintain constant the helicopter attitude.

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The stabilization is obtained through some electro-mechanical actuators, positioned in series of the cyclic pitch and the control of the tail rotor

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COMMUNICATION AND NAVIGATION

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Comunication and navigation frequencies

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The main characteristics of an antenna are: The directivity The gain The polarization The opening and the polarization diagram The efficiency The characteristic impedance The length of the antenna.

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Antennas

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Antennas

The directivity of an aerial is the capacity of an antenna to irradiate or to pick up signals in a specific direction. The directivity of an aerial, in a particular direction, is defined as the ratio between the intensity of the radiation, sent in this direction, and the total power, irradiated in all directions The gain of an antenna provides information about the capacity of transmission and receipt of the analyzed antenna, comparing it with an omni-directional aerial. The gain is expressed in dB (is a logarithmic scale) The efficiency of an antenna is defined as the ratio between the irradiated power and the input power accepted by the feeding cable of the antenna

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The radome is a structure used to protect the antennas from the atmospheric phenomena, such as the wind, the rain, the ice, etc.

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Radome

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Fundamentals of transmission lines

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The transmission line is a circuit that permits the energy transfer between the generator and the antenna.

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There are many different types of transmission lines: • Bifilar • Coaxial

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Modulation

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The most common types of modulation, used in the aeronautical field, are: • AM (Amplitude Modulation) • FM (Frequency Modulation) • Pulse modulation

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The AM modulates the amplitude of the carrier wave, in a proportional way to the amplitude of the modulating signal. The frequency of the carrier wave is the same of that of the modulated signal.

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The FM modulates the frequency of the carrier wave, in a proportional way to the amplitude of the modulating signal.

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Modulation

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In the aeronautical field, the HF communications between 3 to 30 MHz are used for long range communications, such as the oceanic communications This radio can operate in 3 different modes, selectable through a specific knob: AM, USB, e LSB

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HF communication system

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NDB and ADF

The ADF receiver receives and processes the signal from the selected radio station (NDB) The ADF measures the angle between the longitudinal axis of the aircraft and the line that connects the aircraft and the NDB station. This angle is called relative bearing The transmission of waves is subjected to the variation of the height of the ionosphere

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The DME (Distance Measuring Equipment) is a navigational radioaid that provides the aircraft slant distance from a ground station. DME operate from 960 Mhz to 1215 Mhz. The DME is based on the direct wave propagation. The maximum real range of the DME is about 200-300 NM. The accuracy of the DME decreases with increase of range

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The display indicates the distance between the aircraft and the station, measured by the system, the time necessary to cover this distance, and the detected speed of the aircraft. The cockpit instrument shows the distance, travelled by the emitted signal, and so it is the slant distance between the aircraft and the station

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The Instrument Landing System (ILS) is the primary precision approach facility for the civil aviation • ILS system comprises three different elements 1. A localizer: provides lateral steering signals for front course approaches to the runway 2. • A glide slope: provides vertical steering signals for landing in one direction on the runway 3. • Two or three radio markers beacons with a vertical transmission, called outer, inner and middle markers: provide spot checks of position at predetermined distances from the threshold of the runway.

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ILS – Glide slope

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The glide slope receiver is essentially a UHF receiver in the frequency band 328.6 to 335.4 MHz with 150 kHz spacing between channels.

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The signal of the glide slope is composed by two signals: • One signal modulated at 90 Hz • One signal modulated at 150 Hz.

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ILS – Localizer

The localizer and the glide slope signals can be divided into two ideal lobes, one modulated at 150 Hz and the other modulated at 90 Hz. The course signal is obtained when two signals are received with equal intensity. The 150 Hz modulated signal prevails on one side of the runway centerline (blue area), while the 90 Hz modulated signal prevails on the other side (yellow area).

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ILS cockpit indicator

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The operational frequency of the system is selected through the same selector that is used for the VOR. When it tunes the localizer frequency, the system automatically sets the corresponding glide slope frequency.

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ILS: critical and sensitive areas

The ILS critical area is an area of defined dimensions, identified around the localizer and the glide slope antennas, where vehicles, including aircraft, are excluded during the operation of the system. This area protects the functioning of the ILS from unacceptable disturbances caused by the presence of vehicle and aircraft.

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Instead, the ILS sensitive area extends beyond the critical one. In this sector the movements or the parking of aircraft are controlled, in order to prevent that they interfere with the system operation.

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Marker beacons

The purpose of the markers is to provide distance information, while the aircraft is doing the approach procedure. All markers emits a signal at the operative frequency of 75 Mhz. The signals of the each marker differ each other due to the different modulation

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The hyperbolic systems of radio-navigation are all navigational systems that use the geometric proprieties of the hyperbole in order to calculate the aircraft position In order to guarantee a correct calculation of the aircraft position, the main characteristic of all hyperbolic navigational system is the synchronization of the different ground station.

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Hyperbolic system

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The main hyperbolic navigation systems are: 1. • The Loran 2. • The Omega 3. • The Decca.

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The LORAN uses 27 chains of stations. Each chain is made of a main station, called master, and of a variable number of secondary stations, called slave. The minimum number of the slave for each chain is two, while the maximum number is four.

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Loran C • The functioning of the LORAN system is based on a series of chains of ground stations that emit a signal which is then processed by the airborne equipment of aircraft

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The Decca was a hyperbolic radio-navigational system, initially used in the Northern Europe during the Second World War. This system transmitted continuous radio waves at low frequencies (LF).

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In order to determine the aircraft position, the Decca used a comparison of the received signals’ phases, similarly to the OMEGA system

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Doppler effect

The Doppler effects is an apparent variation of the frequency of the radio waves, due to the relative motion of the source of the waves in relation to an observer Apparent increase in frequency: when the transmitter moves towards the receiver Apparent decrease in frequency: when the transmitter moves away from the receiver

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The main task of the FMS is that to assist the pilot in the flight management, doing, in an automatic and optimal way, many activities, which otherwise he must do manually:

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• To integrate and to manage the information provided by all used navigational systems in all flight phases • To calculate in real time the aircraft performances, in terms of ground speed, fuel consumption, endurance. So it permits to reduce the operative costs of the flight mission • To manage in an interactive way the flight plan, according to the information provided by the airborne systems and ATC • To manage the autopilot system, in coupling with the data of the flight plan, in order to follow the calculated and planned route in a fully automatic way

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The GPS (Global Positioning System) is a global navigational satellite system, which provides the aircraft position in every point of the Earth • The dialogue between the satellites and the ground stations happens on 2 UHF frequencies: 1. The 2227.5 MHz, used to send the signals from ground towards satellites 2. The 1783.74 MHz, used to receive in the stations the signals transmitted by the satellites

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The Local Area Augmentation System (LAAS) is an augmentation system of the GPS, based on real-time differential correction of the GPS signal The information provided by the LAAS system is used during the approach and landing phases, because the precision reached by the LAAS systems is about 1 m.

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The Global Navigation Satellite System (GNSS) is a project in via of realization that should join the operation of all the navigation satellite systems, such as the American system (GPS), the Russian GLONASS (Global Navigation Satellite System), and the European system (Galileo), in order to permit the true global navigation.

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This big system should permit the navigation in any point of the Earth, and in any flight phase, through a unique system

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The Primary Surveillance Radar (PSR) is the first instrument for the exercise of the Air Traffic Control (ATC). The PSR operates receiving the signal reflected by the aircraft. The PSR has the advantage to detect and to determine the position of every not cooperative target that reflects the radio signals. The PSR isn’t able to identify any aircraft.

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The Secondary Surveillance Radar (SSR) is the main instrument for the exercise of the Air Traffic Control (ATC). Unlike the PSR, the SSR requests the active collaboration of the aircraft, which must receive the signal and respond with another one. The SSR interrogations are sent in the form of a group of 3 pulses, called P1, P2 and P3. The spacing between the P1 and P2 is constant and it measures 2 microseconds.

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SSR and transponder

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The transponder emits 3 pulses: P1; P2; P3 The spacing between P1 and P2 is 2 micro seconds. The spacing between P1 and P3 pulses, transmitted by the radar antenna, is set at a value of response of the transponder: 1. The mode A with a spacing of 8 microseconds 2. The mode C with a spacing of 21 microseconds

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The TCAS (Traffic Collision Avoidance System) is a system that operates in connection with a normal transponder, informing the flight crew about the presence of other aircraft in the surrounding airspace only if it is equipped with a transponder, and regarding time and distance of possible collision The TCAS transceiver of an aircraft periodically interrogates the transponder of the other aircraft, in order to identify the presence of the airplane and to recognize the characteristics. This aircraft, in situation of possible collision, is called intruder.

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In case of possible collision, the TCAS emits two different signals:

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1. The TA alarm, generated by all TCAS generations, provides to pilots the direction of arrival and the relative distance of the intruder. This type of alarm will be generated on cockpit displays, in the case in which the estimated collision point is between 20 e 48 seconds, in accordance to the speed and altitude of the aircraft. 2. The RA alarm is generated when the intruder is at about 15-35 seconds form the hypothetical collision point, according to the altitude of the aircraft 3. TCAS II: it can provide the Resolution Advisory (RA) for the horizontal and vertical plane

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Weather radar

A weather radar is a type of radar used to locate precipitation, to calculate its motion, to estimate its type (rain, snow, hail, etc) Check the aircraft position in relation to the ground The weather radar of the aircraft sends some directional pulses in the band of microwaves. The frequency commonly used is the 9375 MHz. It is important to remember that the Clear Air Turbulence (CAT), that is very dangerous for the flight safety, cannot be detected by the weather radar, because it isn’t associated with any meteorological phenomena. It mainly identifies the cumulonimbus Another function of this instrument is ground mapping The pencil-shaped beam is used for weather scope It doesn’t measure the height of the elements of the underneath ground

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Weather radar

The weather radar antenna can move up or down from its neutral position of about 10° The precipitations are represented with colors, for example high intensity are RED color, heavy in MAGENTA and black if the intensity of precipitation is less than 0.7 mm/h

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Radio altimeter

The radio altimeter measures the vertical distance between the aircraft and the ground, with the scope to provide to the pilot an information about the underneath terrain. The radio altimeter is used in the approach phase The radio altimeter compares the frequency of the received signal with the frequency of the transmitted signal, because this difference is proportional to the time and the distance travelled by the emitted signal with the frequency between 4200 and 4400 Mhz.

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The ELT (Emergency Locator Transmitter) is an emergency selfcontained and self-powered radio transmitter, designed to transmit a signal on the international emergency frequency in conjunction with the satellites, It is installed near the tail of the aircraft The ELT automatically activates when an aircraft impact happens or by a remote switch in the cockpit.

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ELECTRICAL POWER

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A battery (better a “battery pack”) is a device, which is made of a group of electrochemical cells, utilized to transform the stocked chemical energy into electrical one. These are connected in series, so that the voltage of the single elements is added. The batteries provide Direct Current (DC). The most significant parameters are: • The capacity, expressed in Ampere-hour [Ah], indicates the quantity of stored electrical energy that the battery can deliver from its state of complete charge to its discharged state • The produced energy, expressed in Watt-hour [Wh], indicates the product between the capacity of a cell and its voltage • The energy density, expressed in Watt-hour per Kilogram [Wh/kg], indicates how much energy is produced by a single cell of battery for each its kilogram. 18.01.2017

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The Nickel-Cadmium batteries consist of a steel case containing some cells connected in series The positive electrode is made of nickel hydroxide and the negative one is made of cadmium hydroxide. The electrolyte is a water solution of potassium hydroxide. Each cell of these batteries is able to provide an electromotive force of about 1.2 V.

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Nickel-Cadmium batteries

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The silver-zinc batteries are very expensive and for this reason they are used on aircraft only in the emergency conditions The two electrodes (one electrode made of silver dust and one made of zinc) are drowned in the electrolyte, which is a water solution of potassium hydroxide. Each cell of these batteries is able to provide an electromotive force of about 1.7 V

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Silver-Zinc batteries

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The dynamo has the main advantage of being reversible: it can also be used in opposite way. In fact, the dynamo is able to produce mechanical work starting form electrical energy

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Starter-generator

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AC generator

On civil aircrafts of big and medium dimensions the primary system is designed in AC. The AC, generated on aircraft, has usually a voltage of 115-200 V and a frequency of 400Hz. They are connected in parallel. The variable magnetic field is generated by a permanent magnet that rotates. In this way its magnetic field cuts the stationary wires, so producing an alternating voltage output Generator Control Unit (GCU) is a component of the A/C generators. The GCU regulates the output of the generator.

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The RAT (Ram Air Turbine) is a small turbine that in case of the loss of both primary and auxiliary power sources will power the vital systems The RAT generates power from the airstream (or ram air) due to the speed of the aircraft. The capacity of the electrical generator is usually 7.5 kVA (6W).

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The EPU (Emergency Power Unit) is a turbine activated by a chemical reaction of hydrazine. This turbine is usually installed on military aircraft and it can operate for short period

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Bus-bars

The generated electrical energy is distributed to users through busbars. A bus-bar is a copper bar that connects the power generation system to the users In the electrical system various independent bus-bars exits. Each of them powers a specific number of users according to their importance in the flight safety. For example the essential bus-bars are connected to the primary equipment, and the flight entertainments is connected to the primary and secondary

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A TRU (Transformer Rectifier Unit) is made of a transformer with windings that have the task to lower the voltage usually from 115 A/C to 28 V D/C, and some conductors, usually some diodes, which straighten the sinusoidal voltage in constant voltage. This device is used to charge the batteries

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Transformer Rectifier Units

The most common rectifier is composed by 4 diodes

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• The main characteristics of the TRUs are: 1. High overload capability 2. High efficiency, typically 90%

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External and ground power

The aircraft are generally equipped with 2 sockets, at which the ground units must be connected:

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1. An Alternating Current socket with 6 pins (for example the other big pin, called A, guarantees the bonding) 2. A Direct Current socket with 3 pins (for example the big central pin is that of the voltage These sockets are positioned on the fuselage of the aircraft, near the nose landing gear

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GPU: a mobile airport equipment that provides the electrical power/ IDG: a device that integrates in a single unit a CSD (Constant Speed Drive) and an AC (Alternating Current) generator

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AC – DC Sockets

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Big pin

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EQUIPMENT AND FURNISHINGS

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In-Flight Entertainment (IFE) or Passenger Entertainment System (PES) refers to the on-board entertainment available to passengers during a flight. On long-range aircraft the IFE is provided by personal televisions installed on each passenger seat The IFE systems are usually isolated from the aircraft main electrical system The screens of the cabin have a size from 5 to 42 inches

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Cabin entertainment equipment

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The information displayed by the moving-map system is directly derived from the flight computer of the aircraft system

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Cabin entertainment equipment

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In recent years, IFE has been expanded to include in-flight connectivity services, such as Internet browsing, text messaging, emailing and phone usage (where permitted).

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All these functions are made via the Iridium satellite communication system. It is a personal communication network based on satellites. The Iridium network allows to send and receive voice and data messages in anywhere in the world.

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Electronic emergency equipment

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There are also electronic devices employed for the aircraft localization and the recovery of any parts or scraps. The main electronic emergency equipment are: • The Emergency Locator Transmitter (ELT) • Underwater Locator Beacon (ULB).

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The ELT (Emergency Locator Transmitter) is an emergency selfcontained and self-powered radio transmitter, designed to transmit a signal on international emergency frequencies (121.5 MHz). The ELT transmits continuously for three days, within a coverage range of about 150 NM. For an aircraft with more than 19 passengers there must be at least one automatic ELT

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The ULB (Underwater Locator Beacon) consists of an electronic module, a transducer and a battery contained in a cylindrical aluminum case that is resistant to high pressure and violent impacts. The ULB is usually installed on each black box of the aircraft, in order to facilitate the recovery. Sometimes, this locator is directly installed on the fuselage of the aircraft, while in helicopters it is generally placed at the back.

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FLIGHT CONTROLS

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Trim control

Trim tabs are small surfaces, connected to the trailing edge of aircraft larger control surfaces. They have the function to stabilize the aircraft at a particular desired attitude, without the need for the pilot to constantly apply a control force Using the trim tab, the reduction of the pilot manual force can reach the 100%

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Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack The Krueger flap does not operate in this way because it only increases the wing area and the wing curvature. Krueger flap is the most simple slat

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A yaw damper is a device used on many aircraft to reduce the rolling and yawing oscillations (Dutch roll phenomenon), which can be induced in some maneuvers Yaw damper increases the passengers comfort, ensures the aircraft stability and reduces the work load of the pilot. for an aircraft that has the yaw damper included in its auto-stabilisation system is required a three axis autopilot system

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The rudder limiter system limits the displacement of the rudder at high speeds, in order to prevent rudder overloads. The device is controlled by the RUDDER LIMIT switch. The rudder limiter mechanism consists of an electric actuator, which blocks rudder’s displacement according to indicated airspeed of the aircraft.

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The system monitors airspeed, which is obtained by the flight computers, and restricts rudder’s displacement according to different parameters. • For example: o Full rudder travel (to 30) is permitted at speeds below 150 knots o Intermediate travel (to 15) is permitted at speeds between 150 to 200 knots o Minimum travel (to 5.7) is permitted at speeds above 200 knots.

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A gust lock on an aircraft is a mechanism that locks control surfaces in place, preventing random movement and possible damage of the surface from wind, while the aircraft is parked.

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Fly-by-wire

The FBW system replaces the mechanical actuation of the command, given by the pilot, with an electronic interface. The FBW system interposes some calculators between the pilot and the final control of the actuators or of the aircraft surfaces The FBW systems are classified according to the percentage of use of the electrical components in the system

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Instrument systems - classification

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The main pilotage instruments can be divided into 3 categories: • Static instruments (altimeter, airspeed indicator and vertical speed indicator) • Gyroscopic instruments (artificial horizon, turn and back indicator, directional gyro) • Magnetic instruments (magnetic compass and gyrocompass).

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Static instruments

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The static instrument are called static instruments because their main device is a metallic aneroid capsule with very thin walls. • The capsule measure the difference in pressure. • The static instruments receive pressure from: 1. A static source (positioned in a point where it isn't affected by the aircraft motion) 2. A dynamic pressure (positioned in a point where it is affected by the aircraft motion)

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Altimeter

The altimeter is an aneroid barometer, whose measurements of the atmospheric pressure are converted in altitude parameters The altimeter is made up of a watertight box, connected with the outside through the static source. Inside this box there is the capsule that is hermetically sealed

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Altimeter

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The barometric surfaces of reference, utilized in aviation, are: • The airport surface (QFE) • The sea surface (QNH) • The isobaric standard surface (QNE) For example if, in the setting window, the pressure value of the isobaric standard surface (1013millibar) is introduced, the altitude indications are called “flight levels”. This setting of the altimeter is called QNE. This setting is used during cruise.

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The air speed indicator is the instrument that measures the aircraft speed in relation to the air mass around it. It is made up of a watertight box, connected with the outside through the static source. Inside the box there is the capsule, which is connected to the outside through the dynamic source The expansion of the capsule is bigger as the dynamic pressure, and thus the aircraft speed, is greater. During the flight the dynamic pressure is greater than the static one

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Air speed indicator

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Air speed indicator

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The different colorings identify and delimit fields of the operational speed of the aircraft. The utilized standard colors are: • White • Green • Yellow • Red. The most significant errors of the air speed indicator are: • The error of position • The error of compressibility • The error of density The error of compressibility becomes important when the speed is so high to compress air molecules inside the static source. The CAS corrected by this error is called EAS (Equivalent Air Speed). The TAS is the EAS (Equivalent Air Speed) corrected by the error of density

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The gyroscope is a rigid body that is put in rotation at high speed. The gyroscope is made of a rotating disk (the rotor), which, due to physical laws of conservation, tends to maintain its rotation axis (or spin axis) oriented in a fixed direction

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Gyroscopic principle

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The turn and slip indicator is made up of a gyroscope with 2°of freedom. It is limited to rotate around its vertical axis (Z). The rotational axis of the gyroscope (X) is horizontal and it is parallel to aircraft transversal axis A gravity slip and skid indicator is a very simple instrument that uses both the centripetal and centrifugal forces. The turn and bank indicator has also a gravity slip and skid indicator

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Turn and slip indicator

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Directional gyro

The directional gyro, or heading indicator is made up of a gyroscope with 3° of freedom and with a horizontal spin axis. It is important to remember that the directional gyro moves gradually away from the indications of the compass, due to the apparent precession, the Earth’s rotation and the construction imperfections. These gaps can reach a maximum of 15° per hour, and so they must be manually corrected by the pilot every 15-20 flight minutes. The maximum drift rate directional gyro is typical 1 degree per minute, with an accuracy of 2°. The rose is instinctive

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Errors

Errors are lines exit from the South magnetic Pole and enter in the North Pole The variation error is caused by the fact that the magnetic compass provides indication in relation to the North magnetic pole, which doesn’t coincide with the North geographic pole. The variation is greater at Poles Also the magnetic inclination error especially happens when the magnetic compass is near to the magnetic poles. The deviation error is caused by the airborne presence of ferrous parts and electromagnetic equipment that can divert the flow lines of the Earth’s magnetic field. This error can be compensated thought some compensator magnets. These residual errors, which can be not compensated by the magnets, are typically written on a small table, placed near the compass, as a value to add or to subtract from the indication read on the instrument. It’s important to remember that the values of residual deviation must not exceed 3°.

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In accordance with JAR-OPS 1, a commercial transport airplane must carry a FDR, which uses a digital method of recording and storing flight data.

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The parameters, which must be recorded, vary according to the maximum certificated take-off mass and to the age of the aircraft. All parameters of all aircraft system must be recorded with a common reference time scale. The data must be obtained from the various airplane sources, which will have accurate correlation with the information displayed to the flight crew. FDR is contained in a shockproof box that is able to sustain extremely high impact forces and high temperatures.

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In accordance with EU-OPS 1, a commercial transport aircraft must carry a CVR that must be able to record 4 channels of audio data: All radio voice communications transmitted from or received by the flight crew members • The audio environment of the cockpit, including the cockpit conversation • Voice communications, done through the airplane interphone system between the cockpit and the cabin • All voice signals or other audio signals related to the identification of navigation or approach aids

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The fuel level is measured using the change in electrical capacitance of a capacitor The capacitance of the capacitor depends on the dielectric value existing between the two armatures of the capacitor. An increase in fuel level would increase in capacitance.

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Capacitance probe

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Another type of fuel quantity indicator used in the more modern applications measures the fuel level in the tank by utilizing the emission and reception of sound pulsed-signal by an ultra-sound sensor installed in the bottom of the tank

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Ultra-sound system

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Another device that uses the change in electrical resistance as a function of temperature is the bulb thermometer. It is generally used to measure the operating temperature of fluids inside engines. In these devices the probe consists of a container that encloses an electrical filament, which is placed inside the fluid whose temperature must be taken The selection of the material of the filament (nickel or platinum) depends on the maximum operating temperature envisaged for the thermometer. Nickel is generally used for temperatures up to 300° C, while platinum is suitable for maximum temperatures of 600° C.

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Bulb thermometer

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LIGHTS

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Aircraft lighting may be divided into different groups:

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o External lights: exterior lights provide illumination of the ground during landing and taxi operations and make the aircraft visible in flight.

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o Internal lights: min power 3W  Passenger compartment lights  Cargo and service compartment lights

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o Emergency lights: emergency lights provide interior and exterior illumination of exits and exit paths during emergency evacuation

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Navigation lights

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Navigation lights are an essential system and control is obtained through a relay activated switch in the flight deck. Normal power supply for such lights is 28 V AC from a protected bus such as the essential or standby bus • Navigation lights include a single lamp: 1. Red light on left wing 110° 2. Green light on right wing 110° 3. White light on thetail 140°

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Strobe lights

The larger aircraft can be also equipped with some additional strobe lights, located on the trailing edge of the wings and on the tail. The strobe lights are activated both during the day and the night, in order to encourage the identification of the aircraft both in flight and on ground, especially in the case in which it occupies the runway

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The anti-collision lights system (also called anti-collision beacon lights) mainly consists of one or more red lights, according to the aircraft dimensions. They are flashing rotating lights, which are usually mounted on the top of the fuselage or of the tail. The minimum light intensity is 100 candles (the output is 400 candles) Anti-collision lights are activated when the engines are started up during night flights and daylight hours

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Anti-collision lights

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Landing lights

Landing lights are white and they are installed on the aircraft in order to illuminate the runway during landings and takes-offs The landing lights are generally of the PAR 200-300 W type. Some systems use retractable landing lamps. The fixed part is switched on when the aircraft is authorized to entry in the runway, and it is switched off at 10000 ft

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Runway turnoff lights are white lamps, positioned to illuminate laterally the taxi-ways and the runways for an angle of 50°. These lights are used during the take-off run, during the landing and during the taxi phase During the departure, the runway turnoff lights are switched on at the beginning of the taxi, and they remain activated until 10000 ft.

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Runway turnoff lights

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Logo lights

Generally, the airliners are also equipped with some logo lights that illuminate the company's logo The logo lights remain activated during the night, during the ground operations and during the flight below 10000 ft.

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Taxi light

The taxi lights are designed to provide the illumination on the ground during the taxing phase or when the aircraft is towed on the airport surface The taxi lights don’t provide the same degree of illumination of the landing lights On aircraft with a tri-cycle landing gear, the taxi lights are often mounted on the non-steerable part of the nose landing gear Moreover some aircraft can be equipped with additional taxi lights located on the lower surface of the aircraft nose

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Internal light – Passenger lights

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In the passenger cabin a large variety of lights can be installed. The most of the passenger cabin lights are: • Controlled by the flight crew and flight assistants • Made of fluorescent tubes, connected to some transformers to control the voltage • COCKPIT: some incandescent floodlights with a large luminous beam that are installed on the cockpit ceiling

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ON BOARD MAINTENANCE SYSTEMS

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Central Maintenance System

The line maintenance of the electronic system is based on the use of the Central Maintenance System (CMS)

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The purpose of the CMC is to give a central maintenance aid to intervene on aircraft systems and subsystems through controls located in the cockpit CMC computers are installed in the compartment of the electrical devices

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The aircraft CMS provides:

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An access to maintenance message of all aircraft systems An access to status information about ground tests A loading means of navigational files, data bases and system software A downloading means of maintenance data A means of printing data A means of connecting to the aircraft system computers

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CMS

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The CMS advantages are: • Reduction of duration of operations • Reduction of the maintenance crew training time • Simplification of technical documentation • Standardization of the equipment

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The CMS includes: • Built-In-Test –Equipment (BITE) for each aircraft system • Central Maintenance Computers (CMC) in Boeing Industry • or Centralized Fault Display System (CFDS) in Airbus Industry • MCDU

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CMS

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BITE test

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The BITE can be divided into three categories: Start-up or power Interruptive Continuous

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The BITE monitors the operational parameter and detects the possible failures that can happen, to facilitate the aircraft maintenance in flight and on ground If a failure is detected, the BITE automatically generates the signals and insulate the damaged element

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The BITE has the functions: • To monitor and measure the inputs • To measure and check the output

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Central Maintenance Computer

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In case there is a failure: The left CMC detects a failure The right CMC controls the functioning of the system

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The CMC computers that are installed on aircraft are usually 2 and they are positioned in the compartment of the electrical devices. • In normal functioning: The left CMC sends/receives the signals to the aircraft systems

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CMC menu’

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On ground, first page: • Last leg report • Last leg ECAM report • Previous legs reports • Avionics status • System reports/test

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According to the type of the system installed on board, it can execute different procedures to display the reports

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In flight: • Current leg report • Current leg ECAM report

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Updating of software

It is important to control:

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• The trustworthiness of the software, in order to check that there is no virus • The compatibility of the software with the aircraft systems • The correct installation, through some specific tests.

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Aircraft printer

The printer is usually located on the cockpit central console or on one cockpit side The information are sent to the printer from the CMC, in ARINC 429 binary coded decimal form Inside the printer the data are converted in the language of the device The printer head is heated and it moves over a thermally sensitive paper The post flight report is automatically printed

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Aircraft printer

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AIR CONDITIONING AND CABIN PRESSURIZATION

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Main use of compressed air: pressurization and conditioning system, anti-ice protection, engine start up system.

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Engine bleeding Generation through the APU (Auxiliary Power Unit) Generation through some ground support equipment

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Methods to provide compressed air:

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Air conditioning system

On aircraft, the air conditioning system has the function to maintain comfort environmental conditions (temperature, humidity and air composition) during all flight phases.

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The air conditioning system must be designed to extract and introduce heat in the cabin.

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Comfort conditions must guaranteed also in critical environment.

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Air conditioning system

The pneumatic system takes hot air from the compressor.

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Mixing hot air, taken from the engine, with cold air passed through a refrigerating cycle, it is possible to obtain the air at correct temperature and humidity for the maintenance of the desired environmental cabin conditions.

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Air conditioning system

In order to guarantee the maximum comfort of passengers the air temperature, present in the cabin, must be comprised between 18° C (65° F) and 24° C (75° F)

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The relative air humidity must be about 20-30 %

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In normal conditions, the air conditioning system must guarantee in the cabin an air flow of about 1 lb per minute for each person. This value cannot be less than the half in case of failure of the system

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Main problem: how to heat the air. The air can be heated using an engine exhaust heat exchanger or a combustion heater

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There is not a real conditioning system, they are equipped with a ram air system. The air comes directly from outside the aircraft: same pressure and temperature of the air in which the flight occurs. The air that comes from outside is filtered and heated before entering the aircraft cabin through a series of ducts.

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Small not-pressurized aircraft

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Ram air coming from a forward facing air duct passes through a heat exchanger in which hot exhaust gasses of engine pass. After the air is heated, it enters a chamber in which cold air coming from another aircraft intake flows into. Some valves control the hot and cold air flows in order to reach the desired temperature. At this point the air mixture enters the cabin.

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Exhaust heat exchanger system

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Advantages: cheap and very efficient. Disadvantages: very dangerous in case of an internal leak. This damage can cause carbon monoxide poisoning. In addition this system doesn’t operate if the aircraft is stationary and there are no fans installed.

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Exhaust heat exchanger system

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They use the aircraft fuel to heat the air. The air is provided by a fan, while the fuel is directly taken by the aircraft fuel system. The air-fuel mixture is ignited by a spark plug; the exhaust gases travel through the exhaust outlet.

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Combustion heater system

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Air for the air conditioning system is bled from the engine. Hot air is directly taken from the compressor and it must be cooled to reach a suitable temperature. Hot air, taken from the engine, is mixed with cold air coming from a refrigerating cycle to obtain the desired temperature and humidity

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Large pressurized aircraft

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Large pressurized aircraft

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The air conditioning systems also uses a percentage of recycled air from the cabin. Recycled air is filtered and mixed with pure air.

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Advantages:

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The system must elaborate a smaller external air flow It is possible to maintain the relative humidity around acceptable values, reducing the need to add humidity to the dry air that comes from the refrigerating cycle.

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Air cycle and vapor cycle machines

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Air cooling is achieved using some “packs” that can include two cycles: • Air cycle • Vapor cycle. The number of cooling packs depends on the size of the aircraft. When it is necessary to install more than one pack, these packs work independently to provide air for each compartment they work for.

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Air cycle and vapor cycle machines

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Pack = turbine that drives a compressor on a rotor shaft. The turbine and the compressor wheels are similar: they consist of a cast wheel and some blades made of aluminum alloy. The turbine wheel rotates within a nozzle ring, while the compressor wheel rotates within a diffuser ring

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Air cycle machines – reverse joule cycle Most common refrigerating cycles on aircraft are air cycles.

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Air cycles are thermodynamic cycles in which the air undergoes some transformations in order to reach the desired temperature and pressure conditions.

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• The theoretical refrigeration cycle is a reverse Joule cycle. 1. The external air, flows into the compressor, in which it is subjected to a compression. 2. Then in the second phase an isobaric cooling happens 3. while in the next phase an expansion occurs through the turbine, until the pressure present in cabin is reached 4. The air is expelled from the fuselage by control valves

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Reverse joule cycle

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Bootstrap cycle

Bootstrap cycle = improved standard refrigeration cycle. The fluid is subjected to two compressions and passes through two heat exchangers before entering the turbine. Heat exchangers reduce the air temperature before entering the second compressor and the turbine Fan: connected to turbine and compressor, cools them when aircraft is ground. In flight cooling is provided by the airflow. Water separator: installed after the turbine and before the air flows into the cabin. It provides a whirling movement to the air, to facilitate the formation of microscopic water drops. Then drops are drained to avoid condensation in cabin

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Bootstrap cycle

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Vapor cycle machines

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In refrigerating vapor cycles the air cooling is achieved with a refrigerant fluid. This fluid is able to absorb heat during the evaporation process.

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Major components of a typical vapor cycle machine: • Liquid receiver • Thermostatic expansion valve • Evaporator • Turbo-compressor • Condenser.

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Refrigerant stored in the liquid receiver. From this reservoir the fluid passes in the thermostatic expansion valve and reaches the evaporator. In the evaporator the hot air coming from engines boils the refrigerant and then enters the cabin at a much lower temperature The vaporized refrigerant fluid flows into the compressor (coupled with the turbine) and reaches a high temperature and pressure. Then the hot gas enters the condenser and is cooled by the ram air coming from outside. The refrigerant condenses and it is pumped back to the liquid receiver to start a new cycle.

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Vapor cycle machines

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Vapor cycle machines

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The pressure controller is connected to the outflow valve: it sends some signals to the valve in order to regulate its aperture When the aircraft is on ground, the valves are maintained in the complete open position, in order to ensure the air exchange even if the air conditioning system is activated. After the take-off the valves moves towards the closed position, which is never reached in order to guarantee the air exchange during the flight. Only in the case of failure the outflow valve closes, preserving the cabin pressure, for a time interval sufficient to lead the aircraft at an altitude where the pressurization isn’t necessary.

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Pressure controller and outflow valve

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Safety valve

The safety valve operates when the difference between the cabin pressure and the external pressure is bigger than a specific value utilized for the fuselage design. Generally the safety valves are activated when the cabin pressure exceeds the limit value of about 0.25 psi.

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Additional instruments

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In the cockpit, some instruments, which permit pilot to controls the aircraft pressurization, are installed: o • The cabin altimeter o • The cabin variometer (expressed ft/min) o • The cabin differential pressure indicator • The cabin altimeter indicates the cabin altitude. It remembers that the cabin altitude is defined as the atmospheric height at which the value of the pressure inside the fuselage corresponds. • The cabin variometer controls the pressure rate inside the cabin, referring to the altitude variation per minutes [ft/min] • The cabin differential pressure indicator indicates the pressure difference between the inside and the outside of the aircraft [psi]

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FIRE PROTECTION

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Fire and smoke detection and warning systems

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Detectors are based on temperature and smoke measures. They provide an alarm when a temperature higher than a fixed value is detected, or when an important smoke concentration is present.

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The detection systems: Indicate when a fire starts or stops Provides audio and video warnings

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The detection systems are different according to the aircraft are in which they must be installed

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The most common types of detection systems are: Thermal detectors Smoke detectors

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The characteristics of the detection systems are:

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To create a warning signal after 60 seconds of an abnormal parameter To provide a warning signals after that more than one sensor records anomalies To provide a warning message before to be damaged by the fire To provide a warning message by radio transmission

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Characteristics

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Thermal detector

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The thermal detectors can be divided into: • Unit detectors • Continuous detectors

The unit detectors are based on some bimetallic strips that opens a contact when the temperature is higher than a set parameter

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The continuous detectors are made of a conductor placed in a semi-conductor material

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The smoke detectors are located in: Baggage holds Freight bays Toilets Equipment bays

Smoke detector

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The most common types of the photoelectric smoke detectors are: Light scatter types Light absorption types

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Light scatter types

The light scatter types are based on the principle for which when a light hits a photo-electric cell, it produces a an electric current

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When the air is clean, the light rays does not reach the photoelectric cell

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When in the air the smoke is present light rays start reflecting on the smoke particles and hit the photoelectric cell producind electricity

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Light scatter types

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Light absorption types

The light absorption types have a photoelectric cell that receives all the light when the air is clear

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When smoke is present, the light that reaches the photoelectric cell reduces

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The fire fighting in the cabin is executed by hand with mobile portable extinguishers

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The fire fighting in the remote aircraft areas (engines, avionic bays and cargo compartments) is executed by fixed extinguishers

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The fire fighting is very difficult in case of nacelles

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Fire on aircraft

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Extinguishing systems

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The extinguishing systems are: • Fixed • Portable • Mixed

The fixed systems are permanently installed

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The portable systems includes hand fire extinguishers

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The mixed systems includes fixed pipelines and portable extinguishers

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Extinguishing systems

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FUEL SYSTEM

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Integral tanks

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One of the most used procedures to load fuel is that to utilize wing tanks • The wing tanks are integral tanks that are constructed in the wing structure, completely sealing the section utilized for this scope Wing tanks have also some disadvantages: • The available volume is scarce on supersonic aircraft • On military jets these tanks represent a wide area exposed to bullets • They can suffer of leaks

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The transfer of fuel is very different, according to the number and the type of engines, to the relative position between tanks and engines On multi-engine aircraft, it must be possible to feed any engine with the fuel of any tanks

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Cross-feed and transfer

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Indication and warnings

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Inside the tanks some sensors are installed. These devices detected the level of the present fuel.

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They can be of different types: • Mechanical sensors • Ultrasonic sensors • Capacitive sensors

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The capacity of a capacitor depends, a part of its geometrical characteristics, from the dielectric. In this case, the dielectric is made by the fuel and air, which fill the room between the armatures

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Capacitive sensors

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These devices measure the level of the present fuel, according to an emitted signal, which is reflected by the liquid surface The distance between the sensor (that is the bottom of the tank) and the fuel level is calculated dividing the propagation velocity of the acoustic signal by the time interval between the transmission and the reception of the signal

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Ultrasonic sensors

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Ground refueling

The ground refueling of an aircraft must be done under pressure of about 0.35 MPa, by airport systems or by ground tankers. When some tankers are used, it is necessary to electrically link the aircraft with the tanker, in order to avoid the formation of electrical arches

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HYDRAULIC POWER

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Hydraulic system layout

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A hydraulic system is primarily made of: • Pumps, that generate the pressure and the flow rate requested by the system in a delivery line and low pressure in a return line • Pipes, connections and some valves, that have the task to distribute the hydraulic energy to different devices • Different users, which are connected to actuators that transform the hydraulic energy into mechanical power. Linear actuators are called jack, while rotational actuators are the hydraulic engines; all systems that require activation are connected to these devices • A series of accessories with specific functions, such as filters, accumulators and heat exchangers

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Hydraulic system layout

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Hydraulic fluids

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In the aeronautical sector, fluids used must meet the following requirements : • • Have a good lubricant power • Avoid corrosion • Viscosity must be limited to avoid power losses and overheating, and it must be almost stable in a wide range of temperatures • Good wear resistance, through the addition of additives • Good resistance to formation of contaminated particles that shall damage the components • Low risk of fire • Low toxicity

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Hydraulic fluids

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The fluid types, which are utilized in hydraulic systems, are of two categories:

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Mineral oil is often used on little aircraft and in the shock-absorber of the landing gear. Instead, the synthesis oil is the most used type in large aircraft systems.

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Mineral oil

Mineral oil is generated by the distillation of high quality petrol. These oil types have some characteristics that vary according to the temperature and they have fire risks. They also have good lubricant proprieties. Mineral oils have limited corrosive characteristics in relation to other oil types. This type of fluid is often used on little aircraft and in the shock-absorber of the landing gear

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The synthetic oil is the most used type in large aircraft systems. This product is characterized by : Low degree of oxidation Low coefficient of thermal expansion Low freezing temperature High fire resistance

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Syntetic oil

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Hydraulic pumps

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Aircraft engines Electrical engines Pneumatic engines

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The devices that transform mechanical energy into hydraulic power are called hydraulic pumps Their function is to take the oil from designed reservoirs, and then make it available with a higher pressure to the system and to users

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The hydraulic energy is available by converting the mechanical power that is mainly taken from the following sources:

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Piston pumps

Hydraulic pumps used in aeronautical hydraulic circuits are volumetric pumps These are also called displacement pumps, because they displace a fluid volume and force it into the system A typical example is the piston pump

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Gear pumps

Another example of volumetric pump is the gear pump This device is made of a chamber in which two contra-rotating cogged wheels move The fluid is sucked in areas that develop between sectors of the single wheel and walls of the box When the wheels arrive in the delivery area, the teeth engage themselves and the oil is forced to exit the sectors and then it is pushed in the pipeline The gear pumps are simple and resistant systems, but they are rather cumbersome. In addition they provide less pressure than that provided by a piston pump

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A constant flow rate is desirable for hydraulic systems In the case of the constant pressure system, a valve is installed after the pump. This valve controls the pressure and guarantees a constant value. This valve is a device with a cursor that is normally open. According to the value of the pressure of the system, the opening of the orifice can be varied

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Constant flow rate

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This method is more efficient than the previous one, because the pressure of the system is maintained constant, while the requested flow rate can be easily changed It is an expensive technique

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Variable flow rate

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Actuators

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Actuators are devices that transform hydraulic energy into mechanical power. There are two main types of actuators: • Linear • Rotational.

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Linear actuators are normally called jacks, while rotational actuators are called motors

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ICE AND RAIN PROTECTION

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Ice protection

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The necessity to prevent or to remove ice formations is the main goal of the ice protection system, and its intervention can be happened according two modalities:

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• The prevention of the ice formation (Anti-icing systems) • The ice removal, when the ice is just formed (De-icing systems).

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The aircraft windshield is a wiper system, a rain repellant system and a heating system The Ice identification rod vibrate at a frequency of 40 KHz

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De-icing system

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According to the operational principle these systems are divided into: • Electrical methods • Pneumatic methods • Chemical methods. The de-icing pneumatic system has the disadvantage that to cause a disturb in the wing aerodynamic, also when elastic elements are flat.

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If the system uses fluid the temperature of the fluid must be greater than the ambient temperature.

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Anti-icing system

The systems, which have the scope to prevent the ice formation, are called anti-icing systems.

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According to its operational principle, they can be divided into: Hot air methods Electrical methods (probes and sensors) Chemical methods

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Rain repellent

The external fluid spray system comprises a de icing fluid tank connected by a pipe line to an electrically operated pump, the delivery side of which is coupled to a spray device arranged in front of the windscreen. This system is used in case of heavy precipitation in order to improve the pilot visibility.

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LANDING GEAR

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Shock absorbing

The shock absorber represents the main component of the landing gear and it has the task to absorb energy during its deformation, giving back only a part of it while dissipating the rest in form of heat In the aeronautical sector, the most common type is the oleopneumatic shock absorber

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The brakes must absorb the kinetic energy, transforming it in heat, and so they are subject to a remarkable heating. The brakes are composed by a series of discs coupled to the rim and the pistons that act to them.

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Brakes

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Landing gear systems

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On aircraft other two systems are installed. These systems, which are very important, are: • Antiskid system • Autobraking system

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The core body of the tire is a multi-layer of nylon fibers, which are positioned along different directions and drown in the rubber.

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Tires

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Light aircraft are commonly provided with the nose-wheel steering capability, provided by a simple system of mechanical linkage hooked to the rudder pedals. Instead, large aircraft utilize a power source for the nose-wheel steering. This system is necessary because large aircraft have larger mass and heavier weight. During taxiing, steering hand-wheels (one for the pilot and one for the co-pilot) are used to control the direction of the aircraft. The steering hand-wheel provides 75° of nose wheel deflection both in left or right direction. Signals from each hand-wheel are summed up

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Steering

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An important phenomenon that is connected to the employment of the landing gear is the shimmy. Shimmy is a summarizing term for the torsion flutter phenomenon of aircraft landing gears. A way to oppose the phenomenon consists in installing the shimmy damper on the landing gear. The shimmy damper is a little piston able to provide the necessary damping to cancel or reduce vibrations

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Shimmy

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Most aircraft and helicopters utilize some type of Weight On Wheel (WOW) Sensor or Switch that activates when the aircraft is on the ground A faulty or incorrectly adjusted WOW system may cause vital systems to not function or function intermittently

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Air-ground sensing

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OXYGEN

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Oxygen system

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The pressurization system fails There is the presence of fumes or gasses One or more passengers have medical difficulties

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On civil aircraft the oxygen is supplied only in emergency conditions, when:

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Oxygen system

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The supply should last at least 15 minutes at a pressure altitude of 8000 feet at 30 liters per minute • On civil aircraft, the system, dedicated for the oxygen supply in the cockpit, requests the installation of a particular tank that generally operates at 1850 psi (12.7 MPa). • In particular: 1. • Provision of oxygen mixed with air on demand 2. • Provision of oxygen only on request

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Oxygen system

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Crew oxygen system

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To install some supply circuits, dedicated to the passengers and the flight crew To equip the aircraft with some oxygen tanks/bottle (both fixed and portable)

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The technical solution used for the emergency oxygen system is double:

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Crew oxygen system

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The installation of a particular tanks operating at 1850 psi A distribution net must reach every single certificate position of the crew Some regulations to allows the flow to come into the mask Some masks, one for each crew member

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On civil aircraft, the system dedicated for the cockpit oxygen supply, requests:

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Crew oxygen system

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Crew oxygen system

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Chemical oxygen generators

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Chemical oxygen generators

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The chemical oxygen generators are made by: A metallic container A candle of chlorate sodium A pressure detonator

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The chemical oxygen generators are especially used for the passenger cabin oxygen system

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The oxygen is produced by the exothermal reaction developed in the candle

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Chemical oxygen generators

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Oxygen system

The information about the oxygen system is displayed on the lower right corner of the DOOR/OXY page. The OXY writing indicates the value of the pressure of the oxygen. This value is expressed in psi. When it is normal, the information is displayed in green (Green band and black rectangular symbol on white back-ground), while if the value is too low the number is colored by the amber

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Oxygen system

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On military jets, the pilot breathing is guaranteed through a mask, similar to that of the picture. This mask is usually used during the whole flight, and the oxygen concentration, that it provides, varies according to the aircraft altitude

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Oxygen system on military jet

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PNEUMATIC AND VACUUM

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Pneumatic system - users

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The pneumatic system works at 10MPa that correspond to a 2 to 8% bleed from compressor The main users of the pneumatic system usually are: • The pressurization and the conditioning system • The anti-ice system • The system dedicated to the start-up of engines.

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A check valve is installed so that when the APU is not running air from the pneumatic manifold cannot back feed through the APU Air pressure from the APU is controlled by altering the inlet guide vanes to the load compressor

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APU

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The pneumatic system is automatically controlled and monitored by 2 BMCs. There is one BMC for each engine bleed system. However, both BMCs are interconnected and if one fails, the other takes-over most of its functions (NOT ALL)

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Indications and warnings

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Indications

The information concerning the pneumatic system is also displayed on the lower part of the ECAM BLEED page. On this page the valves of the pneumatic system are represented by a little circle, with a line inside

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WATER AND WASTE

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Potable water system

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Storage: • Potable water is stored in a small tankers • The stored water must be sufficient for the whole flight • A quick and clean refilling must be allowed Heating: • The water must be heated to the right temperature for the hot water taps • The water must be enough heated to make hot drinks Cooling: • The water of the drinking fountains must be cooled

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Potable water system

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Distribution: • The pressure must be enough to force the water to all taps, heaters and beverage makers Contents indication: • The cabin crew must be able to control the water level during the flight • The technician must be able to control the quantity of loaded water Anti-frost system: • It prevents the water freezing in the supply pipes • Some Electrical heaters are placed around the pipes Removal of waste water: • The waste water must be removed from sinks, drinking fountains towards the outside of the aircraft

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Toilet system can be classed into three groups: Removable toilets, often called Elson type Re-usable toilets liquid flush type Clean water flush type, or vacuum flush type The sink water is drained outside the aircraft

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Water and waste system

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The flush type single toilet unit has a sink that distributes hot and cold potable water, and a WC that uses instead a management system of black water. This system is made of a tank containing a liquid, which is treated with chemical additives. These substances protect from the fermentation and the development of bacteria

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Flush type

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Corrosion aspect

The toilets, especially the sinks, are the places in which the corrosion starts. The toilet floor does not have an easy access for maintenance and is subject to moisture, so it is a common place where corrosion can start (It must be used floor panel sealings) To avoid corrosion it is necessary to provide some extra protection. A strong corrosion resistant material is the titanium.

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INTEGRATED MODULAR AVIONIC

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Electronic sets operated on aircraft generally are summarized as “avionic = aviation electronic equip-ment A new concept, labeled “Integrated Modular Avionic (IMA)”, first presented by Honeywell for cockpit functions on the Boeing 777 aircraft in 1995 A strong SW/SW partitioning and HW/SW segregation characterize the IMA

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SW= software HW= hardware

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IMA - Introduction

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Core Processing and IO Module (CPIOM)

The Core Processor Input/output Module (CPIOM) is the controller and it is common avionics computer resources supporting most of the software implemented functions of the aircraft across all aircraft system domains. The CPIOM is a standard hardware platform designed to host several independent aircraft functions.

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For example, CPIOMs for the Utilities domain perform fuel management, measurement and display, as well as the landinggear extension and retraction systems, braking, and the aircraft's nose-wheel steering software. CPIOMs in the Energy domain use the standardized architecture to control electrical power distribution.

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It concentrates data from analog and discrete signals remotely (for example, in proximity to associated sensors and actuators) and then communicates this data to computer processing resources on the aircraft The CRDC is an avionics unit generally installed outside of the avionics compartment.

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Common Remote Data Concentrator (CRDC)

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Chapter 13,21

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CABIN SYSTEMS

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The Cabin Intercommunication Data System, or CIDS, gives the interface between the flight crew (cabin/cockpit) and the cabin systems The main improves for new CIDS are related to the exclusive use of touch-screen interfaces, common software platform and a common, user-friendly interface to obtain fleet uniformities and to reduce costs (components and specialization courses). These systems are generally operated by means of control panels, especially the cabin attendant panels.

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Cabin Intercommunication Data System (CIDS)

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Cabin Network Service (CNS)

The Cabin Network Service (CNS) is a new kind of system that allows interconnecting the entire aircraft system to the available services: communication, entertainment, diagnosis system, flight data, etc.

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The principle of operation of the CNS can be compared to that of a common pc network where the data runs on wires and transmits information to all the connected stations.

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The first advantage is that with a single wire it is possible to transmit more information to different LRUs and on board systems.

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The satellite television is the most recent innovation for in flight entertainment system The covered area and the relative satellite are: West Europe (ASTRA and HOTBIRD) East Europe, Russian zone (EUTELSAT W4) North Africa and Mid-East (ARABSAT and NILESAT) India (INSAT 4B)

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In-flight entertainment system

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INFORMATION SYSTEM

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Means of storing

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On modern aircrafts memories used are SSD Solid State Drive that have completely replaced the older technology based on the Hard Disk Drive HDD. SSD shows a breaking risk lower than an Hard Disk Drive because in a SSD there are no moving parts. Moreover o SSD doesn’t need defrag o SSD is more shock resistant than the HDD o SSD produces less heat than the HDD • Usually this kind of drive is based on flash memory. Flash memories use the features of Floating Gate MOSFET (metal-oxidesemiconductor field effect transistor) a field effect transistor able to store electric charge for a long time. • The limit of flash memories is that they cannot be wrote and read limitless like hard disk drives therefore they have lifecycles 18.01.2017

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