Hydraulics

[Spanner Turner]

From the 747 Maintenance Manual;


CAUTION:
DURING OPERATIONS INVOLVING HYDRAULIC SYSTEMS PRESSURIZATION, RELATED INSTRUMENTS AND INDICATING LIGHTS IN THE FLIGHT COMPARTMENT SHOULD BE CLOSELY MONITORED TO ASSURE SATISFACTORY OPERATION OF SYSTEM. IF HYDRAULIC FLUID OVERHEAT CONDITION OCCURS, SYSTEM OPERATION SHOULD BE DISCONTINUED.
DO NOT OPERATE TRAILING EDGE FLAPS MORE THAN TWO CYCLES IN A 15 MINUTE PERIOD. SYSTEM LOADING CONDITIONS CAN OVERHEAT HYDRAULIC FLUID.

Check for a minimum of 300 gallons (2000 pounds; 900 kilograms) of fuel in each No. 1 and 4 main fuel tanks, and 805 gallons (5400 pounds, 2450 kilograms) in each No. 2 and 3 main fuel tanks.
NOTE: If the applicable tank has the minimum amount of fuel, there is no time limit on the operation of the hydraulic pump. If there is less fuel than the minimum amount, the hydraulic pump operation is limited to 15 minutes.

CAUTION: TO PREVENT HYDRAULIC FLUID OVERHEAT, DO NOT OPERATE PUMPS AFTER OVERHEAT LIGHT COMES ON OR LONGER THAN 15 MINUTES WITHOUT MINIMUM QUANTITIES OF FUEL IN TANKS. ALLOW 20-MINUTE COOLING PERIOD AFTER 15-MINUTE OPERATION OR AFTER OVERHEAT LIGHT GOES OUT. WHEN AMBIENT TEMPERATURE EXCEEDS 100¡F, OPEN NACELLE STRUT FAIRING DOORS. EXTREME TEMPERATURES AND LOAD CONDITIONS CAN OVERHEAT HYDRAULIC FLUID.


The above outlines operations in the Maintenance environment and it would be extremely unlikely to encounter a hydraulic overheat and near to impossible in a "Flight" condition. But like anything in aviation, "It's possible"


.