29-21-00
 ALL  ú ú 03 Page 8 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

 WARNING: FOR AIRPLANES DELIVERED PRIOR TO L/N 128 AND WITHOUT SB
_________
 757-29A0032 INCORPORATED

 THE RAT AUTO CIRCUIT BREAKER ON PANEL P11 AND RAT MANUAL CIRCUIT BREAKER ON PANEL P6 MUST BE OPEN BEFORE PERFORMING PITOT STATIC SYSTEM TESTING. IF SIMULATED PITOT PRESSURE EQUAL TO 80 KNOTS IS APPLIED WITH ENGINES OFF, THE RAM AIR TURBINE WILL DEPLOY.
 FOR AIRPLANES DELIVERED WITH RAT AIR/GROUND LOGIC (L/N 128 AND ON) OR EARLIER AIRPLANES WITH SB 757-29A0032 INCORPORATED
 THE RAT AUTO CIRCUIT BREAKER ON PANEL P11 AND RAT MANUAL CIRCUIT BREAKER ON PANEL P6 MUST BE OPEN BEFORE PERFORMING PITOT STATIC SYSTEM TESTING. IF SIMULATED PITOT PRESSURE EQUAL TO 80 KNOTS IS APPLIED WITH ENGINES OFF AND THE AIRPLANE IN THE AIR MODE, THE RAM AIR TURBINE COULD DEPLOY.
 (a)  
In the ground mode, the air/ground system No. 1 relay removes power from the RAT arm Q airspeed switch and provides power to the RAT ground manual switch. While the airplane is on the ground, the RAT can be deployed with either the RAT deployment switch on the pilot's overhead panel P5 or the RAT ground manual switch inside the fairing panel on the right wheel well aft bulkhead. The RAT deployment switch deploys the RAT the same as in-flight deployment and does not provide control to stop the RAT once deployment is started. The RAT ground manual switch deploys the RAT and provides control to stop the RAT at any point during deployment.

 (b)  
When the ground manual switch is held in the DEPLOY position the RAT control valve motor is energized. The valve moves to position No. 2 (ground position) and connects the deployment actuator pressure port to the RAT safety valve. In position No. 2 the valve switch closes to energize the deploy solenoid on the RAT safety valve. In the deploy position, the safety valve connects the actuator pressure port to the right hydraulic system return line. This allows fluid to flow out of the actuator as it deploys by spring force. When the ground manual switch is in the DEPLOY position the auto solenoid unlocks the deployment actuator.

 (c)  
The ground manual switch returns to the OFF position, if released. This de-energizes the safety valve which moves to the closed position. In the closed position, the valve blocks fluid flow from the actuator and stops RAT deployment.

 (3)  Retraction
 (a)  The RAT can be retracted only while the airplane is on the ground and with the right hydraulic system pressurized.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 29-21-00
 ALL  ú ú 02 Page 9 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

 (b)  
The RAT turbine hub must be moved to align index marks on the hub and strut. When the ground manual switch is moved to the STOW position power is applied to the safety valve retract solenoid. The safety valve moves to the retract position which connects right system pressure to the actuator pressure port. Hydraulic pressure drives the actuator to the retracted position, stowing the RAT. As the actuator retracts, the deployment springs inside are compressed. A mechanical lock holds the actuator in the retracted position.

 (c)  
When the RAT reaches full stow and locked position the RAT control valve is cycled to position No. 1 (air position). The pressure and return ports of the actuator are connected to the right system return line. The RAT is then ready for automatic (air) release.
　
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