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Background Information
Boeing has received reports of GE engine flameout and subsequent engine
recovery while operating in heavy rain. In one dual engine flameout incident,
digital flight data recorder (DFDR) information revealed the autothrottle was
engaged and commanding a thrust increase from approach idle when the
flameouts occurred. While the reported flameouts occurred in heavy rain, water
ingestion by itself has been ruled out as the sole cause of these events. Engineering
analysis of DFDR data has determined the most likely cause to be rapid variable
bleed valve (VBV) closure resulting from autothrottle thrust increases during
sustained engine ingestion of supercooled water and ice.
General Electric has investigated the problem and is planning an EEC software
update, which will reschedule VBV operation to reduce engine susceptibility to
flameout under the conditions encountered during the reported incidents.
Operating Instructions
Flight through areas of heavy precipitation should be avoided. However, if heavy
rain or hail cannot be avoided or is inadvertently encountered, disconnect the
autothrottle and minimize thrust changes to reduce the possibility of engine
flameout. The MODERATE TO HEAVY RAIN OR HAIL procedure reflects
these instructions.
Page 2 of 2
Operations Manual Bulletin No. ILF2-28(R2), Dated April 1, 1999 (continued)
Administrative Information
Insert this bulletin behind the Bulletin Record page in Volume 1 of your
Operations Manual. Amend the Bulletin Record to show bulletin ILF2-28(R2)
INCORPORATED (INC).
This condition is temporary until the system is modified. This bulletin will be
revised to include Service Bulletin information when available.
Mailing Address:Manager, Flight Technical Publications (747-400)
Boeing Commercial Airplane Group
P.O. Box 3707 MS 20-89
Seattle, WA 98124-2207
USA
Fax: (206) 662-7812
Telex: 32-9430 Station 627
SITA: SEABO7X
CS3 - 2546 Page 1 of 4
Sect Name Section Name
Operations Manual Bulletin
for
The Boeing Company
Seattle, Washington 98124-2207
International Lease Finance Corp.
Number: ILF2-33(R2)
Date: April 1, 1999
Document Effectivity: D6-30151-425
Subject: UNCOMMANDED AUTOPILOT ENGAGEMENT, FLIGHT MODE
CHANGES, AND IAS/MACH WINDOW SPEED CHANGES
Reason: To advise flight crews of the possibility of uncommanded autopilot
engagement, flight mode changes, and IAS/MachWindow speed
changes, and provide recommended temporary instructions for these
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
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.
situations. Revised for administrative purposes.
Background Information
UNCOMMANDED AUTOPILOT ENGAGEMENT AND FLIGHT MODE
CHANGES
Boeing has received reports from operators of uncommanded autopilot
engagement and flight mode changes. The reports document at least one rejected
takeoff and one undesired heading change. Engineering investigation has
determined these anomalies are caused by faulty MCP push-button switches
installed during production or subsequent component repair. Intermittent switch
malfunction can cause this anomaly without pilot action. The normal means for
disengaging the autopilot, Autopilot Disengage Switches and the Autopilot
Disengage Bar, are unaffected by this anomaly and operate normally.
Page 2 of 4
Operations Manual Bulletin No. ILF2-33(R2), Dated April 1, 1999 (continued)
UNCOMMANDED IAS/MACH WINDOW SELECTED SPEED CHANGES
Boeing has also received reports from operators of unexpected transition from
selected speed to 0.84 Mach upon multiple channel autopilot engagement during
automatic approach, and upon autopilot disengagement. Under these conditions,
the selected IAS/MACH Window speed changes to 0.84 Mach, requiring pilot
intervention to regain airspeed control. Investigation has determined these
anomalies occur only with older flight control computers (FCC S241T100-133
and earlier).
Operating Instructions
This bulletin does not apply to airplanes modified by SB 747-22A2214.
UNCOMMANDED AUTOPILOT ENGAGEMENT
Flight crews should closely monitor PFD flight mode annunciations for autopilot
status, and be prepared to respond to uncommanded autopilot engagement during
critical phases of flight, including takeoff. Uncommanded autopilot engagement
　
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