(5)
The flap segments are mechanically separated during extension to increase the effective flap area and to reduce stagnation of the air flowing over the flap surface. The flaps remain together as they begin extension forming a single slot between the foreflap and wing trailing edge. At approximately 5 units extension the foreflap carriages contact a stop on the flap tracks. Further extension of the flaps moves the midflap and aftflap relative to the foreflap, forming a slot between the foreflap and midflap. At approximately 15 units extension for the outboard flaps and 20 units extension for the inboard flaps, the cam action of the aftflap actuating mechanism begins to separate the aftflap from the midflap. Further flap extension forms a slot between the midflap and aftflap.
(6)
The FCU load relief function automatically retracts the flaps at high airspeeds to prevent excessive airloads on the flaps. Airspeed values from the air data computers are checked against flap lever position by the FCU. The EICAS advisory message >FLAP RELIEF is displayed while flap load relief is occurring.
(a)
With the flap lever at the 25-unit detent, the FCU's will position the flaps to 20 units when airspeed exceeds 203 knots, and back to 25 units when airspeed drops below 195 knots.
(b)
With the flap lever at the 30-unit detent, the FCU's will position the flaps to 20 units when airspeed exceeds 203 knots, and then to 25 units when airspeed drops to between 170 and 195 knots, and to 30 units when airspeed drops below 170 knots. Flaps will retract to 25 units again if airspeed exceeds 178 knots.
(c)
If airspeed data from both air data computers is invalid or absent, the EICAS status message FLAP LOAD RELIEF is displayed.
C.
Control
(1)
General
(a)
During maintenance the flaps are normally operated with hydraulic power. If hydraulic power is not available, the flaps are operated in primary or alternate electric mode. The drive systems for the inboard flaps and outboard flaps are separate and independent. On the ground the inboard flaps and outboard flaps may be independently operated with either hydraulic or electric power.
CAUTION: TO PREVENT HYDRAULIC FLUID OVERHEAT, DO NOT OPERATE PUMPS
_______ AFTER OVERHEAT INDICATOR COMES ON OR LONGER THAN 15 MINUTES WITHOUT MINIMUM QUANTITIES OF FUEL IN TANKS. ALLOW 20-MINUTE COOLING PERIOD AFTER 15-MINUTES OF OPERATION OR AFTER OVERHEAT INDICATOR GOES OUT. WHEN AMBIENT TEMPERATURE EXCEEDS 100° F (38° C), OPEN NACELLE STRUT FAIRING DOORS. EXTREME TEMPERATURES AND LOAD CONDITIONS CAN OVERHEAT HYDRAULIC FLUID.
(b) Hydraulic system No. 1 operates the inboard flaps and hydraulic system No. 4 operates the outboard flaps. If the air-driven hydraulic pump is used to supply hydraulic power, repeated cycling of the trailing edge flaps may overheat the pump.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
(2) Normal (Primary Hydraulic) Operation
CAUTION: DO NOT OPERATE TRAILING EDGE FLAPS WITH PANEL 293C OR 294C
_______ (AMM 6-09-04/201) LOOSE OR REMOVED FROM AIRPLANE. DAMAGE TO HARDWARE CAN OCCUR.
(a) Provide electrical power (Ref 24-22-00/201).
WARNING: TRAILING EDGE FLAP, AILERON, SPOILER, RUDDER AND ELEVATOR
_______ CONTROL SURFACES AND LANDING GEAR ARE FULLY POWERED. PRIOR TO PROVIDING HYDRAULIC POWER, CHECK THAT PERSONNEL AND EQUIPMENT ARE CLEAR OF SURFACES. LEADING EDGE FLAPS WILL AUTOMATICALLY EXTEND AS THE TRAILING EDGE FLAPS ARE EXTENDED.
(b)
Provide hydraulic power (Ref 29-11-00/201).
(c)
Extend flaps fully by placing flap control lever in 30 unit detent.
(d)
Retract flaps fully by placing flap control lever in FLAP UP detent.
(3)
Primary Electric Operation
WARNING: WITH ELECTRICAL POWER AVAILABLE, EVEN THOUGH HYDRAULIC AND
_______ PNEUMATIC POWER ARE OFF, ALL TE AND LE FLAPS WILL AUTOMATICALLY EXTEND OR RETRACT WHEN THE FLAP LEVER IS MOVED. PRIOR TO MOVING FLAP LEVER, CHECK THAT PERSONNEL AND EQUIPMENT ARE CLEAR OF TE AND LE FLAP SURFACES.
CAUTION: DO NOT OPERATE TRAILING EDGE FLAPS WITH PANEL 293C OR 294C
_______ (AMM 6-09-04/201) LOOSE OR REMOVED FROM AIRPLANE. DAMAGE TO HARDWARE CAN OCCUR.
(a) Provide electrical power (Ref 24-22-00/201).
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