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D6-27370-866-EGP B-26 Page 1 of 2
CoversFile HighlightImpact of Arming VNAV on the Ground on the Windshear Escape Maneuver (FMC Update 10.8 and 10.8A)EGP-26
Flight Crew Operations Manual Bulletin
for
Egyptair
Number: EGP-26
IssueDate: January 10, 2011
Subject: Impact of Arming VNAV on the Ground on the Windshear Escape
Maneuver (FMC Update 10.8 and 10.8A)
Reason: This bulletin informs 737NG flight crews of the need to revise the
windshear escape maneuver if VNAV has been armed on the ground for
takeoff (FMC Update 10.8 and 10.8A).
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
Background Information
During airline simulator evaluations of FMC Update 10.8A, an unintended
consequence of arming VNAV for takeoff was discovered with respect to the
windshear escape maneuver. If VNAV is armed on the ground, it will remain
armed even if TO/GA is pressed below 400 feet AFE in accordance with the
windshear escape maneuver. At 400 feet AFE, VNAV will engage and windshear
guidance will be lost. TO/GA must be pressed a second time when above 400
feet AFE in order to regain the appropriate windshear guidance.
This condition exists on FMC Update 10.7, 10.8 and 10.8A. Arming VNAV on
the ground is not permitted prior to Update 10.8, however.
Boeing and GE are discussing a potential fix for this anomaly in a future FMC
software update.
Operating Instructions
Arming VNAV on the ground is not permitted with FMC Update 10.7 or earlier.
With U10.8 or 10.8A installed, if unstable weather conditions are present prior to
takeoff, consider not arming VNAV for takeoff.
The Boeing Company
Seattle, Washington 98124-2207
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.
September 24, 2015
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