B767/29/101 Hydraulic System
Boeing 767-200/300
Hydraulic System Training manual For training purposes only LEVEL 1
ATA 29
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B767/29/101 Hydraulic System
Training manual
This publication was created by Sabena technics training department, Brussels-Belgium, following ATA 104 specifications. The information in this publication is furnished for informational and training use only, and is subject to change without notice. Sabena technics training assumes no responsibility for any errors or inaccuracies that may appear in this publication. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of Sabena technics training.
Contact address for course registrations course schedule information Sabena technics training
[email protected]
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TABLE OF CONTENTS 1. HYDRAULIC POWER. ............................................................................................................6 2. CONTROL & INDICATION. ..................................................................................................12 3. GROUND SERVICING. .........................................................................................................18 3.1. Reservoir Filling. .................................................................................................................18 3.2. Ground Power Connections. ..............................................................................................20 3.3. Engine Driven Pump S.O.V. ................................................................................................22 3.4. Engine Driven Pump EDP. ...................................................................................................24 3.5. ACMP (Alternating Current Motor Pump). .........................................................................26 4. PTU (PWR. TRANSFER UNIT) = PES (PITCH ENHANCEMENT SYSTEM). ...........................28 4.1. Reserve Brakes & Steering. .................................................................................................32 4.2. Air Driven Pump.................................................................................................................34 4.3. RAM Air Turbine (RAT). ......................................................................................................36
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LIST OF ILLUSTRATIONS AIR DRIVEN PUMP (ADP) ........................................................................................................ 35 ALTERNATING CURRENT MOTOR PUMP (ACMP) .................................................................... 27 E.D.P. SHUTOFF VALVE LEFT & RIGHT SYSTEM ........................................................................ 23 ENGINE DRIVE PUMP LEFT & RIGHT SYSTEM .......................................................................... 25 FLIGHT COMPARTMENT INDICATIONS & CONTROLS.............................................................. 13 GROUND POWER CONNECTIONS .......................................................................................... 21 HYDRAULIC CONTROL & INDICATION.................................................................................... 15 HYDRAULIC GROUND SERVICING .......................................................................................... 19 HYDRAULIC SYSTEM ............................................................................................................... 7 HYDRAULIC SYSTEM GENERAL ................................................................................................ 9 RAM AIR TURBINE (RAT)......................................................................................................... 37 RESERVE BRAKES & STEERING SYSTEM .................................................................................. 33 STABILIZER PTU SCHEMATIC .................................................................................................. 30 STATUS & MAINTENANCE INDICATIONS ................................................................................ 17
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ABBREVIATIONS AND ACRONYMS ACMP APU BKS BTB C/B CTL DN ECS EDP ELCU ELEC FLT FWD GND GPM ISLN ISO LDG LRU MSG OVHT OVSP PB PTU QTY RF RMP RSV RTO SOV STRG TURB UNLKD
Alternating Current Motor Pump Auxiliary Power Unit Brakes Bus Tie Breakers Circuit Breaker Central, Control Down Electronic Cooling System Engine Driven Pump Electronic Load Control Unit Electric, Electrical, Electricity Flight Forward Ground General Processing Module Isolation International Standardization Origanisation Landing Gear Line Replaceable Unit Maintenance Steering Group, Message Overheat Overspeed Policy Board Power Transfer Unit, Power Transformer Unit Quantity Radio Frequency Revolutions per minute Reserve Rejected Takeoff Shut-off Valve Steering Turbine UNLOCKED
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1. HYDRAULIC POWER. General. Three hydraulic systems are identified by location, and the tubing runs are color coded : - LEFT system is RED coded, - RIGHT system is GREEN coded, - CENTER system is BLUE coded. Hi pressure and critical return lines are made from titanium. Aluminium is used for noncritical return lines. Stainless steel tubing is used in designated fire zones. NOTE : To keep the movement of the fluid between the systems to a minimum, pressurize the R SYST before you pressurize the CENTER and the LEFT systems. Also remove the pressure from the center and the left systems before you remove the pressure from the right systems.
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SYSTEM
CENTER
LEFT - RED
RIGHT
- BLUE
- GREEN
PRIMARY SOURCE - (1) EDP (ENGINE GEARBOX DRIVEN PUMP) - (1) ACMP DEMAND PUMP
- (2) ACMP’s
- (1) EDP
- (1) ADP (AIR DRIVEN PUMP)
- (1) ACMP
EMERGENCY
- (1) RAT (RAM AIR TURBINE)
COLOR CODE
LOCATION
SYSTEM FLUID CAPACITY
- MOST OF THE COMPONENTS LOCATED IN : - LEFT ENGINE STRUT
- R. (L.) WHEEL WELL
- R. ENGINE STRUT
- 17 GALLONS
- 40 GALLONS
- 20 GALLONS
NOTE : - THE EDP DELIVERS ± 37 GPM AT TAKE-OFF POWER - ALL EDPÔs ARE INTERCHANGEABLE, WITH THE ADP - ALL ACMPÔs ARE IDENTICAL AND INTERCHANGEABLE, THE PUMP DELIVERS ± 11 GPM
HYDRAULIC SYSTEM
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Reservoirs. Each reservoir is pressurized by air from the pneumatic system. All reservoirs can be filled from one GND SERVICING SYSTEM located in the right aft wing to body fairing. Heat exchangers in the fuel tanks cool the pump case drain fluid before it returns to the reservoirs. Left & right system. The EDP runs continuously when the ENG. is running. An EDP depressurization valve (solenoid), controlled by the ENG. pump switch, stops the fluid flow from the pump. The ACMP can be run in the : - ON mode : The pump runs continuously, - AUTO mode : The pump will start automatically for an EDP low press (± 1900 psi). NOTE : The right ACMP runs continuously in AUTO mode, aircraft on GND and the flaps in take off position (to assure brake pressure in case of RTO). The left ACMP is inhibited on GND during starting of either engine to reduce electrical loads on the APU generator. A PTU (in STAB. compartment) provides reserve left system hydraulic power to operate the stabilizer trim if failure of the left and center systems occurs.
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Center System. Two ACMP’s run continuously when the ELEC pump switches are ON. The ADP can run in the : - ON mode : the pump runs continuously (powered by ENGINE BLEED AIR). - AUTO mode : starts automatically when the system demand exceeds the output of the two ACMP’s. The RAT is stowed in the right wing/body fairing and deploys (by an electric motor) : - AUTOMATICALLY when in FLT, airspeed greated then 80 knots, the ENGINE SPEED (N2) drops below 50 % in both engines. - MANUALLY, anytime, controlled by a switch on the P5 panel. Control and Indication. The indicating system monitors fluid : - Pressure, - Temperature, - Quantity. Amber caution and advisory lights on the hydraulic system control panel. Messages on the EICAS system. On the P5 control panel each system is arranged in a vertical row. Each system row contains ,primary and secondary pump control switches and warning lights (amber). Primary pump switches are press-to-active type and contain ON lights and LOW PRESS lights. The secondary pumps (which are the demand pumps) are controlled by three positions rotary switches.
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HYDRAULIC SYSTEM GENERAL
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T S H C I G I N R H Y C P E O T C A N E B A S page 10 12 - 04 - 2012 rev : 1
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Distribution. - Primary FLT CTL actuators and A/P servos are powered by all three hydraulic systems. Note that the middle RUDDER actuator is supplied throughout the rudder ratio changer. - The spoilers are single powered, but uses power from all three systems. - Most of the FLT CONT are supplied through normal open ISO valves. These are maintenance valves and only closed on GND for maintenance purposes. Six valves are installed, three WING and three TAIL shut off valves. Each valve is, electrically controlled by a push button on P61. - The stabilizer is powered by the right/center system and PTU provides a third source in case of a failure of the left and center systems. The PTU is automatically controlled. - FLAPS/ SLATS are single powered by the center system. FLAPS/SLATS have an electrical backup system. - The LDG system is single powered by the center system. The brakes are normally powered by the right system and in case of low pressure there will be an automatic switch over to the center system. - In the center system, the ACMP1 is normal supplied by a stand pipe in the center reservoir, and throughout two (2) ISO valves. These valves consist of a supply and a pressure shut off valve. They provide a reserve system to power the brakes and nose wheel steering if C system pressure is lost (in FLT and C SYST. LOW QTY) or when RESERVE BKS & STRG is selected. When the system is activated, fluid is supplied to ACMP1 from the bottom of the reservoir. Than the pressure from ACMP1 is routed only to the NOSE GEAR (steering) and alternate BRAKES.
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2. CONTROL & INDICATION. EICAS display units (P2). Hydraulic system caution and advisory messages are displayed on the upper EICAS display unit. Additional information and messages are available on status and maintenance level pages which are displayed on the lower unit. Overheadpanel (P5). The main hydraulic control panel contains primary and demand pump controls and indications as well as system pressure and quantity caution lights. The ram air turbine manual deploy switch is located on the engine start panel. Aft control stand (P8). The engine fire switches control fluid supply to the engine driven hydraulic pumps and pump depressurization. Side panel (P61). Flight control shutoff valve switches control operation of 6 valves that can isolate hydraulic flow to the wing and tail systems. Caution Messages. * L Hyd Sys Press * C Hyd Sys Press
Advisory Messages. L HYD QTY
L DEM HYD OVHT
C HYD QTY
R DEM HYD OVHT
R HYD QTY
C HYD 1 OVHT
**L HYD PRIM PUMP
C HYD 2 OVHT
C HYD PRIM 1
L PRIM HYD OVHT
C HYD PRIM 2
R PRIM HYD OVHT
**R HYD PRIM PIMP
C DEM HYD OVHT
L HYD DEM PUMP
RAT UNLOCKED
C HYD DEM PUMP
RSV BRAKE VAL
R HYD DEM PUMP * Inhibit pump low pressure messages in the same system. **Inhibited with, associated fuel control switch in cutoff
* R Hyd Sys Press
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FLIGHT COMPARTMENT INDICATIONS & CONTROLS EFFECTIVITY ALL
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Hydraulic Panel. System Pressure (SYS PRESS) Lights. • Illuminated (amber) - system pressure is low.
Ram Air Turbine. RAM AIR Turbine (TURB) Switch • Push - deploys the RAT.
Reservoir Low Quantity (QTY) Lights. • Illuminated (amber) - reservoir quantity is low.
Ram Air Turbine Pressure (PRESS) Light. • Illuminated (green) :
Left/Right Engine (L/R ENG) Primary Pump Switches. • ON - the engine-driven hydraulic pump pressurizes when engine rotates. • Off (ON not visible) - the engine-driven hydraulic pump is turned off and depressurized. Pump Pressure (PRESS) Lights. • Illuminated (amber) - pump output pressure is low. Pump Overheat (OVHT) Lights. • Illuminated (amber) - pump temperature is high. Center 1/2 Electric (C1/2 ELEC) Primary Pump Switches. • ON - the electric motor-driven pump pressurizes the center hydraulic system. • OFF (ON not visible) - the electric motor-driven hydraulic pump is turned off and depressurized. Left/Right Electric and Center, Air (L/R ELEC and C AIR) Demand Pump Selectors. • OFF pump off. • AUTO : * Pump operates when engine pump pressure is low, * Pump operates when heavy load items are selected (Air Demand pump only).
* The RAT is deployed, * The RAT is producing hydraulic pressure. Ram Air Turbine Unlocked (UNLKD) Light • Illuminated (amber) - The RAT is not stowed and locked. Reserve Brakes & Steering Reset/Disable Switch. Reset/Disable Switch : • RESET/DISABLE - Resets or disables the automatic isolation feature of the center hydraulic system. • NORM - The isolation feature is armed for automatic operation. Isolation (ISLN) Light. Illuminated (white) - The number one hydraulic pump on the center hydraulic system is isolated to provide hydraulic pressure to the reserve brakes and steering system. FLT CTL Shutoff Switches. • ON - The flight control valve is commanded open. • Off (ON not visible) - The flight control valve is commanded closed. Flight Control Shutoff OFF Lights. Illuminated (amber) - The flight control valve is closed.
ON- continuous operation.
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HYDRAULIC CONTROL & INDICATION EFFECTIVITY ALL
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Status & Maintenance Indications. Status page indications. Fluid quantity is available to the flight crew on the status page. Quantity is indicated as a digital readout with 1.00 indicating full. The need for refilling is indicated by RF next to the quantity indication. System pressure is available on the status page as an option. Maintenance page indications. Fluid quantity, system pressure and reservoir fluid temperature are available to ground maintenance personnel on the ELEC/HYD maintenance page. A reservoir overfill condition is indicated by an OF next to the quantity indication. Auto events caused by low system pressure, low fluid quantity or pump overheat are also indicated here. The ECS/MSG maintenance page will provide an O/FULL message when a reservoir is overfilled and a HYD SYS MAINT message when system pressure is below 2800 psi for 60 seconds, with system low-pressure indications off and both engines running. The HYD SYS MAINT message is also displayed on the status page and is an auto event.
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STATUS & MAINTENANCE INDICATIONS
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3. GROUND SERVICING. 3.1. Reservoir Filling. The reservoir service station is located in the right-hand aft body fairing area immediately aft of the RH wheel well. NOTE : To attain a proper fluid level in the reservoirs, the reservoirs must be serviced with : - All landing gears down, - Gear doors closed, - Steering and flight controls neutral. When servicing right system the brake accumulator pressure gage must read at least 2500 psi. The hydraulic quantity gauge is calibrated in percent of full increments (110 % 1.1) with a green band between .80 and 1.1 indications. Two sight glasses are installed on each reservoir. The lower REFILL sight glass gives indication to replenish reservoir. The upper OVERFILL sight glass gives indication to drain reservoir to FULL level. A pressure-fill port, service filter and a hand pump with handle and suction hose are also located in the reservoir service station.
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HYDRAULIC GROUND SERVICING EFFECTIVITY ALL
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3.2. Ground Power Connections. General. The 767 hydraulic system may be pressurized by an external power source. Ground service self-sealing connections are provided in each of the three systems. Left and right systems. The pressure connection for each system is located on the EDP filter module and the return connection is located on the return filter module in the respective engine strut hydraulic bay. Center system. The pressure and return connections are located inside a compartment at the bottom wheel wells.
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GROUND POWER CONNECTIONS EFFECTIVITY ALL
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3.3. Engine Driven Pump S.O.V. The engine driven pump supply shutoff valves are : - Located in each engine strut, accessible through the engine strut left access panel. - Two position valves, electrically operated and normally open. - Controlled by the associated ENGINE FIRE SWITCH. - Powered from the 28V DC battery bus. When a valve is selected closed, the EDP depressurization solenoid is also energized. A red position indicator shows the valve position. The valve cannot be manually operated. PUMP OPERATION MORE THAN 5 MINUTES WITH A CLOSED VALVE AND ENGINE RUNNING MAY DAMAGE THE PUMP.
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E.D.P. SHUTOFF VALVE LEFT & RIGHT SYSTEM
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3.4. Engine Driven Pump EDP. The EDP has a maximum flow rating of 37 gpm at 3700 rmp at 2850 psi. Pump output is approximately 24 gpm at idle engine, speed. The pump is depressurized (no flow condition) by powering a solenoid operated valve. This directs pressure to the compensator valve to reduce yoke angle and to the blocking valve to cut may be powered by the pump control switch (P-5) in the OFF position or by using the fire handle. The compensator spring controls the flow-pressurization relationship such that system the pressure is maintained at approximately 3000 psi. EDP Control. As the pump is switched to the “‘OFF” condition, the white “ON” is hidden by a mechanical shutter and the pump depressurization solenoid valve is energized to close and prevent further fluid flow to the system. The pump will continue to run as long as the engine rotates. Their is no time limit to pump operation while depressurized as, long as a supply flow to the pump is available. The pressure light is always active and will illuminate when the pump is depressurized or pressure at pump outlet is low (at or below 1900 psi). An EICAS advisory message will identify the pump (i.e., L HYD PRIM PUMP).
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ENGINE DRIVE PUMP LEFT & RIGHT SYSTEM EFFECTIVITY ALL
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3.5. ACMP (Alternating Current Motor Pump). ACMP’s in the L & R system are demand pumps. ACMP’s in the C system are primary pumps. The 4 pumps are identical and interchangeable. 2 options are available, ABEX or VICKERS pump’s. Caracteristics : - 11 5V AC three phase, - OVHT indication for : 107 OC (fluid cool), - Delivers : ± 6 gpm at 2.850 psi at 5700 rpm. ± 12 gpm at 1.200 psi. PUMP OPERATION NEED AT LEAST 600 gal/1.800 kg FUEL otherwise the limit operation is 10 minutes (20 min. cooling). Vibration plates are replaced with the pump. The pump have self-sealing disconnects.
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ALTERNATING CURRENT MOTOR PUMP (ACMP) EFFECTIVITY ALL
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4. PTU (PWR. TRANSFER UNIT) = PES (PITCH ENHANCEMENT SYSTEM). The PTU is the third power source for the stabilizer in case of failure of the LEFT and CENTER system.
Return Compensator Module. The return compensator module is installed in the return line.
The PES uses the R SYST hydraulic pressure to pressurize an isolated portion of the L SYST.
The bypass valve is spring loaded closed and opens only if the return pressure is more than spring force.
The PTU is installed in the STABILIZER compartment.
When the L HYD. SYST. is operating correctly, fluid coming from the STAB. TRIM MODULE flows through the return compensation. When the compensator is full, the press increases until it opens the bypass valve.
PTU Operation. The L. ISO will close if : - In FLT and, - The L SYST PRESS below 1.275 psi. or, - The L SYST QTY below 0.48. The R. ISO will open if : - In FLT and a stabilizer manual TRIM SIGN. - A C SYST PRESS below 1.275 psi. and - A close sign to the L. ISO valve.
When the PTU is operating, the L ISO valve is closed. The fluid in the compensator becomes a source of (fluid for the PTU inlet. Feel Pressure. A relief valve will close when pressure at the STCM feel computer is less than 100 psi., preventing loss of isolated left system hydraulic fluid through the elevator feel part.
Both ISO valves have a position indicator/manual override lever. The motor uses 3.2 gpm at 1.600 psi from the R. SYST. The pump supplies then 2.7 gpm at 1250 psi to the L. SYST. A flow restrictor limits fluid flow to ± 4.1 gpm.
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PTU Operation. System Description. The power transfer unit is commanded ON automatically to provide hydraulic power to drive the stabilizer in the event both left and center hydraulic systems fail. System Control. Operation of the PTU is controlled automatically. When the airplane is in the flight mode and the reservoir quantity in the left system is below 0.48 or the left EDP and left ACMP pressures are low, the left system isolation valve is commanded closed to isolate the fluid retained by the return compensator. The valve remains closed until 20 seconds after one of the conditions closing the left system isolation valve is removed. If the center hydraulic pressure is low at the time that a manual electric trim command is signaled by either the captain’s or the first officer’s control wheel stabilizer trim control switches, the right system PTU shutoff valve is commanded to open. Hydraulic flow to the PTU motor starts the operation of the pump. The PTU shutoff valve is commanded to close immediately when the stabilizer electric trim command is removed or the center hydraulic system pressure is restored.
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Left Hydraulic System Isolation Valve. When the airplane is in the air, air/ground stem No. 2 connects the left hydraulic system isolation valve controls to the left hydraulic system pressure and the hydraulic quantity indication of the left reservoir. The left hydraulic system isolation valve, closes under either of the following conditions : - The hydraulic quantity monitored in the left reservoir falls below 0.48, - The left hydraulic pressure produced by the EDP and the ACMP is low. If one of these conditions is removed, the left hydraulic system isolation valve remains closed for an additional time of 20 seconds to prevent nuisance signals of short duration from operating the isolation valve intermittently. Right Hydraulic System Shutoff Valve. When the left hydraulic system isolation valve is commanded closed, the right hydraulic system shutoff valve is controlled by the control wheel stabilizer trim control switches and the center hydraulic system pressure. Loss of center hydraulic system pressure and a stabilizer electric trim command from either the captain’s or the first officer’s control wheel switches, cause the right hydraulic system shutoff valve to open and start PTU operation. The right hydraulic system shutoff valve remains open as long as a stabilizer electric trim signal is present and the center hydraulic pressure is low. When the stabilizer electric trim signal is removed, or the ,center hydraulic pressure is restored, the right hydraulic system shutoff valve is commanded to close.
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STABILIZER PTU SCHEMATIC EFFECTIVITY ALL
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THIS PAGE IS INTENTIONALLY LEFT BLANK
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4.1. Reserve Brakes & Steering. Pressure isolation valve. A motor-driven valve that shuts off hydraulic pressure to all center hydraulic pressure to all center systems except nose wheel steering and the alternate braking system. Supply Isolation Valve. A motor-driven valve that switches the No. 1 ACMP hydraulic supply from the reservoir stand pipe to the bottom of the reservoir to access the reserve fluid supply below the stand pipe. Reserve Brakes & Steering Switch. A lighted push-button switch containing a white ON light and amber VALVE light located on the P1-3 panel.
B767/29/101 Hydraulic System
With the reserve brakes and steering switch in the off position, both pressure and supply isolation valves will operate to the closed and alternate positions respectively when center system fluid reaches LOW quantity level and the airplane is in the air. The pump (C-1) then must be activated by pressing the reserve brakes and steering switch. A white ISLN light on the P-61 right side panel will illuminate when either isolation valve is not in the open position. While the reserve brakes and steering is selected on, center system pressure will still be transmitted to the EICAS computers. However the system low pressure switch (S-35) is isolated from pressure causing the center system low pressure light to illuminate.
Reset/disable Switch. A toggle switch on the P-61 panel to reset the automatic isolation system or to disable the auto function while performing ground maintenance. Operation. Actuation of the reserve brakes & steering switch turns on C system N° 1 ACMP unit, if off, and illuminates an ON in the switch. Electric power is first supplied to drive the pressure isolation valve to the closed position. When fully closed, the pressure isolation valve directs power to drive the supply isolation valve to the alternate position. An amber VALVE light in the lower half of the reserve brakes and steering switch will illuminate to indicate a disagreement between the commanded position and the position of either valve. If the disagreement exists for six seconds an EICAS advisory message “RSV BRAKE VAL” will be annunciate.
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RESERVE BRAKES & STEERING SYSTEM EFFECTIVITY ALL
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4.2. Air Driven Pump. Location. The air driven pump is located left aft wing to body fairing. It is accessible by a hinged door. Components. Regulator shut off valve (LRU) :
Pump : - Is the secondary pump in the center system, - 37 gpm, 2.850 psi at 5700 rpm, - Pump turbine speed is reduced during low flow demand, - The pump shuts off when turbine speed decreases to 2500 RPM, - The case drain line of the pump is cooled through a heat exchanger.
- Spring loaded closed, - Electro (solenoid) pneumatic valve, - Pressure regulator ± 13 psi., - An overspeed of the AIR TURBINE will close the valve (de-energizing the solenoid). The solenoid must be reset by a switch on P36. Muffler (LRU) : - reduces the noise. Modulating valve (LRU) : - Spring loaded closed, - Electro (2 solenoids) pneumatic valve, - The valve controls air pressure to the turbine drive, regulating the turbine speed, - The valve opens when the demand or the continuous solenoid is energized.
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AIR DRIVEN PUMP (ADP)
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4.3. RAM Air Turbine (RAT). General. The ram air turbine is the EMERGENCY POWER SOURCE for the FLT CONTROLS if both ENGINES are lost. It is located inside the R. AFT BODY FAIRING. Is manual (PB) or automatically controlled, and deployed or stowed by an electrical DC motor. A press switch senses pressure output and turns on the green PRESS light. Two variable pitch blades are controlled by a counterweight and a governor. Governed speed is - 4.165 rpm at a minimum airspeed of 125 knots.
B767/29/101 Hydraulic System
For a complete retraction of the RAT, the blade must be centered and the locking pin in place. UP/DN limit switches shutoff power at full DN or full UP travel limits. An override limit switch is used during manual DN selection. The tachometer provides visual indication of the operating status of the RAT during GND TEST : - GREEN light is ON : turbine speed is at normal governed speed. - RED light is ON : turbine overspeed. - NO light is, ON : turbine speed is below the normal governed speed. - LAMP TEST : depressing the switch, with the RAT operating, both indicate lights should illuminate.
ON GND. the RAT can be retracted, with the retract select switch in the R. wheel well. Prior to retracting, the propeller blades must be aligned (index marks). The compartment door is mechanically connected to the RAT annunciator. The check out module is used to check the RAT operation on GND. In the back-drive position, the pump acts as a motor driving the turbine. An amber UNLKD light indicates that the RAT is not in STOWED position. A teleflex cable unlocks the turbine blade, opens blade lock and centered switch when the RAT is extended. A 15° limit switch permits partial retraction of RAT so that blade can be locked and centered. The RAT will retract the first 15° trough the strut angle notch. A 13° limit switch operates in parallel with the 15° switch, in the RAT retract circuit.
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RAM AIR TURBINE (RAT) EFFECTIVITY ALL
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