29-21-00
 ALL  ú ú 08 Page 526 ú Jan 28/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL

 S 215-177
 (15)
 When the turbine blade speed has become stable, make sure the green light on the RAT tachometer is on, and the red light is off.

 S 815-178

 (16)
 If the RAT tachometer overspeed light comes on, quickly release the Ground-Checkout module handle and consult the fault isolation section, under the heading "RAT overspeed light on while performing RAT system test".

 S 735-179

 (17)
 If the green light on the RAT tachometer does not operate, you can do these steps to do a check of the speed of the RAT turbine blades:

 (a)  
Release the control handle from the back-drive position.

 (b)  
Remove the power from the center hydraulic system
 (AMM 29-11-00).

 (c)  
Move the lifting fixture below the safety screen.

 (d)  
Lift the safety screen support with the lifting fixture until the support touches the screen.

 (e)  
Remove the bolts and move apart the forward and aft cages of the safety screen.

 CAUTION:_______REMOVE THE SAFETY SCREEN FORWARD CAGE CAREFULLY. IF THE CAGE TOUCHES THE TURBINE BLADES IT CAN CAUSE DAMAGE TO THE BLADES OR THE GOVERNER MECHANISM.

 (f)  
Move the forward cage away from the RAT with the lifting fixture.

 (g)  
Apply a strip of tape that is 1/2 by 2 inches, at one of these locations: 1) On the RAT turbine hub, from the center to the edge 2) On the end of one RAT turbine blade.

 CAUTION: SET THE SAFETY SCREEN FORWARD CAGE TO THE CORRECT HEIGHT
_______ BEFORE YOU MOVE IT INTO POSITION. IF THE CAGE TOUCHES THE TURBINE BLADES, IT CAN CAUSE DAMAGE TO THE BLADES OR THE GOVERNER MECHANISM.
 (h)  
Raise the forward cage to the correct height with the lifting fixture.

 (i)  
Carefully move the forward cage into position around the RAT so that the cage does not hit the turbine blades.

 (j)  
Install the bolts to connect the forward and aft cages of the safety screen.

 (k)  
Lower the lifting fixture and move the fixture away from the safety screen.

 (l)  
Pressurize the center hydraulic system (AMM 29-11-00/201).

 (m)  
Move the control handle on the RAT checkout module, in the right wheel well, to the back-drive position.

 (n)  
Set the stroboscope to less than 1500 rpm.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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 ALL  ú ú 08 Page 527 ú Jan 28/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

 (o)  Monitor the speed of the RAT turbine blades while you increase
 the adjustment of the stroboscope from 1500 rpm to 9440 rpm.
 (p)  Make a record of the highest speed at which the strip of tape
 shows as one stable mark in the light of the stroboscope.
 (q)  Make sure this speed is between 3980 and 4720 rpm.
 NOTE:____ If the governor in the RAT hub does not control the
 speed correctly, a speed in the range of 1500 to 7500
 rpm can occur.

 S 865-180
 (18)
 Quickly release the control handle from the back-drive position. Make sure the RAT green pressure light on the engine start/RAT control panel comes on.
　
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