MN-FLT-OH-201
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Uncommanded Nose Down Stabilizer Trim Due to Erroneous Angle of Attack (AOA) During Manual Flight Only
GOT-13
Flight Crew Operations Manual Bulletin
for
Gol Linhas Aereas S.A.
Number:
GOT
-
13
IssueDate:
November 6, 2018
Airplane Effectivity: 737-8 / -9
Subject:
Uncommanded Nose Down Stabilizer Trim Due to Erroneous Angle of
Attack (AOA) During Manual Flight Only
Reason:
To Emphasize the Procedures Provided in the Runaway Stabilizer Non-
Normal Checklist (NNC).
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
Background Information
The Indonesian National Transportation Safety Committee has indicated that
Lion Air flight 610 experienced erroneous AOA data. Boeing would like to call
attention to an AOA failure condition that can occur
during manual flight only.
This bulletin directs flight crews to existing procedures to address this condition.
In the event of erroneous AOA data, the pitch trim system can trim the stabilizer
nose down in increments lasting up to 10 seconds. The nose down stabilizer trim
movement can be stopped and reversed with the use of the electric stabilizer trim
switches but may restart 5 seconds after the electric stabilizer trim switches are
released. Repetitive cycles of uncommanded nose down stabilizer continue to
occur unless the stabilizer trim system is deactivated through use of both STAB
TRIM CUTOUT switches in accordance with the existing procedures in the
Runaway Stabilizer NNC. It is possible for the stabilizer to reach the nose down
limit unless the system inputs are counteracted completely by pilot trim inputs
and both STAB TRIM CUTOUT switches are moved to CUTOUT.
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
