MN-FLT-OH-201
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Bleed System Oscillations
GOT-5
Flight Crew Operations Manual Bulletin
for
Gol Linhas Aereas S.A.
Number:
GOT
-
5
IssueDate:
March 15, 2018
Subject:
Bleed System Oscillations
Reason:
To inform the crew of bleed system oscillations with Engine Anti-Ice
ON and Wing Anti-Ice OFF.
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
Background Information
During flight test the 737-8 has exhibited bleed system pressure oscillations.
These oscillations were observed with takeoff or climb thrust set with Engine or
Wing Anti-Ice ON or OFF. The oscillations have also been observed at reduced
thrust settings during cruise or descent with Engine Anti-Ice ON and Wing Anti-
Ice OFF. During the bleed system oscillations the L and R needles on the Bleed
Air DUCT PRESSURE Indicator, located on the forward overhead panel, can
fluctuate approximately plus or minus 10 psi out of phase with one another. This
condition does not have any adverse effects on aircraft systems.
The oscillations are caused by unanticipated interaction of both the engine bleed
air valves and the electronically controlled Flow Control Valves (eFCV). Boeing
is working on the fix to these oscillations and will communicate appropriate
implementation instructions as soon as possible.
737-7/8/-9 models are affected by this bulletin.
Operating Instructions
If bleed system oscillations are observed as described above, no crew action is
needed.
Information in this bulletin is recommended by The Boeing Company, but may not be FAA approved
at the time of writing. In the event of conflict with the FAA approved Airplane Flight Manual
(AFM), the AFM shall supersede. The Boeing Company regards the information or procedures
described herein as having a direct or indirect bearing on the safe operation of this model airplane.
March 1, 2021
