RAM AIR TURBINE SYSTEM -EXTENSION -FUNCTIONAL DESCRIPTION

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777 AIRCRAFT MAINTENANCE MANUAL

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RAM AIR TURBINE SYSTEM -FUNCTIONAL DESCRIPTION -RETRACTION

General

You use the stow lever on the RAT checkout module to retract the RAT.
The center hydraulic system supplies the pressure to retract the RAT.
Hydraulic Control

The RAT stow valve and the RAT module solenoid valve both control the retract pressure to the RAT actuator.
The RAT stow lever manually controls the RAT stow valve. A solenoid automatically controls the solenoid valve.
Electrical Control

The RAT strut angle switch and the RAT blade locked switch control electrical power to the solenoid valve.
The strut angle switch is closed when the RAT is between the full down and the 15 degrees from full down position. The switch opens when the RAT is more than 15 degrees from full down.
The RAT blade locked switch is closed when the blade lock pin engages one of the holes on the turbine to lock the blades. This occurs when the RAT is 9 degrees or more from the full down position.
EFFECTIVITY
BEJ ALL

The RAT stow valve position switch supplies the ground for the RAT module solenoid valve when the stow valve is in the STOW position.
Retraction Sequence
When you move the stow lever to the STOW position, electrical power goes through the strut angle switch to energize the solenoid valve.
The solenoid valve moves to permit hydraulic pressure to go to the stow valve.
The stow valve sends pressure to the retract side of the RAT actuator to start retraction.
If the RAT blades are aligned, the blade lock pin engages the hole in the turbine when the RAT has retracted 9 degrees. This closes the RAT blade locked switch and lets the RAT move to the stowed position. Mechanical locks in the RAT actuator lock the RAT in this position.
If the blades are not aligned, the blade locked switch does not close. The RAT stops when the strut angle switch opens at 15 degrees and closes the RAT module solenoid valve.
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RAM AIR TURBINE SYSTEM -FUNCTIONAL DESCRIPTION -RETRACTION

Training Information Point

You must manually align the RAT turbine blades before RAT retraction.
If you release the RAT stow lever during retraction, the lever moves to the STOP position and the RAT retraction stops.
RAT retraction time is approximately 45 seconds.

HYDIM CL monitors the position of the RAT stow valve through the RAT stow valve position switch. If the stow valve is not in the FLIGHT position, HYDIM CL sends a signal to the AIMS to show the RAT DEPLOY INOP status message.
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RAM AIR TURBINE SYSTEM -FUNCTIONAL DESCRIPTION -RETRACTION

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RAM AIR TURBINE SYSTEM -FUNCTIONAL DESCRIPTION -IN-FLIGHT OPERATION

Hydraulic Operation

After in-flight extension, the RAT turbine turns. The start-up quantity bypass fuse lets the initial RAT output go to return. This unloads the hydraulic pump to permit the RAT to spin-up faster.
After spin-up, the start-up quantity bypass fuse closes and RAT pressure goes to the center hydraulic system flight controls.
Speed Control

The governor in the governor-generator assembly changes the blade angle to keep the RAT speed constant.
Indication

The RAT pressure transducer sends RAT pressure data to the HYDIM card CL. HYDIM CL sends this data to the AIMS. The hydraulic maintenance page format shows RAT data.
HYDIM also turns on the pressure light on the RAT switch when RAT pressure is more than 1500 psi.
Training Information Point

The minimum airspeed of 115 knots is necessary for the RAT to supply rated capacity.
When the RAT is extended and hydraulics off, the airplane rolls left. Two to three units of right control wheel rotation are necessary to hold the wings level.
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RAM AIR TURBINE SYSTEM -FUNCTIONAL DESCRIPTION -IN-FLIGHT OPERATION

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RAM AIR TURBINE SYSTEM -FUNCTIONAL DESCRIPTION -MOTORING

General

A functional test of the RAT may be done with the RAT checkout module. This test uses center hydraulic system pressure to operate the RAT pump as a motor to turn the turbine.
　
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