ELEVATOR AND TAB CONTROL SYSTEM - MAINTENANCE PRACTICES
1. General
A. The elevator hydraulic systems A and B must be depressurized prior to performing maintenance on elevator control system components. This is to prevent possible injury to personnel working in the area of the elevator and its associated control linkage. Care must be exercised to locate maintenance stands and items of ground equipment beyond the limits of elevator travel.
WARNING: PRESSURIZING THE HYDRAULIC SYSTEM ALSO ACTIVATES THE RUDDER, SPOILERS, TRAILING EDGE FLAPS, LEADING EDGE FLAPS, AND AILERON HYDRAULIC SYSTEMS. ISOLATE OR TAG ANY SYSTEM NOT BEING TESTED TO PREVENT INJURY TO PERSONNEL OR DAMAGE TO AIRPLANE AND EQUIPMENT.
B. When operating hydraulic system B pumps to pressurize A and B elevator systems the following precautions must be taken:
(1)
At least 1675 pounds (761 kilograms) of fuel is required in the No. 2 fuel tank to provide hydraulic fluid cooling. On hot days or when fuel temperature is known to be above 90°F, monitor the system B overheat indicator and switch pumps off when overheat is indicated.
(2)
Intermittent system B pump operation is limited to five starts of any one pump in a 5-minute period. Following the fifth start run pump for at least 5 minutes or turn pump off for a minimum of 30 minutes.
C. During several of the elevator system adjustment and test procedures, it is required that the mach trim actuator be set to the null position. The electrical positioning procedure specified in par. 5 is to be used.
D. The following procedure covers pressurization of hydraulic systems A and B through operation of electrical-driven hydraulic system B pumps only.
2. Equipment and Materials
A. Flight Controls Lock Assembly - F80049-12 (Preferred) or F80049-1 (Optional) (2 required for depressurization of elevator hydraulic systems A and B)
B. Ground Lock Assembly - F72735 (required for pressurization of elevator hydraulic systems A and B)
C. Elevator Mach Trim Actuator Checking Bar - F80196-1 (required for checking that actuator is in null position.
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May 01/99 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 27-31-0 Page 201
3. Elevator Hydraulic Systems A and B Depressurization
A. Depressurize elevator hydraulic systems A and B.
(1)
Position hydraulic pump switches A and B, located in center of forward overhead panel, to OFF. (See figure 201.)
(2)
Check that ground interconnect switch is at CLOSE position.
(3)
Position flight controls hydraulic systems A and B switches, located in upper left corner of forward overhead panel, to OFF. (See figure 201.)
(4)
Open flight controls circuit breakers located on panel P6.
(5)
If any hydraulic components are to be removed, depressurize hydraulic system reservoirs. Refer to 29-09-300, Hydraulic Reservoir Pressurization System - Maintenance Practices.
(6)
Move control column fore and aft through full travel to relieve hydraulic system pressure.
(7)
Check that manual override lever on flight controls shutoff valve on both flight controls A and B hydraulic modular packages is in position 2. (See figure 202.) Manually place levers in position 2 if required.
(8)
Disconnect electrical connector from flight controls shutoff valve motor on flight controls A hydraulic modular package in left wheel well, and from flight controls shutoff valve motor on flight controls B modular package in right wheel well.
(9)
Install lock to each of the two flight controls shutoff valves and insert attaching lockpins.
B. Restore airplane to normal.
NOTE: Perform following steps after completing elevator control system maintenance that required depressurization.
(1)
Remove locks from systems A and B flight controls hydraulic module shutoff valve and reconnect electrical connectors.
(2)
Position flight controls hydraulic systems A and B switches on forward overhead panel to ON.
(3)
Close flight controls circuit breakers on panel P6.
(4)
Pressurize hydraulic reservoirs as required. Refer to 29-09-300.
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27-31-0 Page 202 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Feb 15/73
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