737 Flight Crew Operations Manual
Hydraulics -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 13.20.7
Standby Hydraulic System Leak
If a leak occurs in the standby system, the standby reservoir quantity decreases to
zero. The LOW QUANTITY light illuminates when the standby reservoir is
approximately half empty. System B continues to operate normally, however, the
system B reservoir fluid level indication decreases and stabilizes at approximately
72% full.
Variations in Hydraulic Quantity Indications
During normal operations, variations in hydraulic quantity indications occur
when:
• the system becomes pressurized after engine start
• raising or lowering the landing gear or leading edge devices
• cold soaking occurs during long periods of cruise.
These variations have little effect on systems operation.
If the hydraulic system is not properly pressurized, foaming can occur at higher
altitudes. Foaming can be recognized by pressure fluctuations and the blinking of
the related LOW PRESSURE lights. The MASTER CAUTION and HYD
annunciator lights may also illuminate momentarily.
September 28, 2006
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