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can be corrected by disengaging the autopilot.
UNCOMMANDED FLIGHT MODE CHANGES
Flight crews should closely monitor PFD flight mode annunciations for
autothrottle, roll, and pitch status, and be prepared to respond to uncommanded
mode changes during critical phases of flight, including takeoff. Uncommanded
flight mode changes can be corrected by selecting the desired mode on theMCP.
UNCOMMANDED IAS/MACH WINDOW SPEED CHANGES
Flight crews should closely monitor command speed on the PFD and be prepared
to respond to uncommanded changes to 0.84 Mach under the following
conditions:
1. multiple channel autopilot engagement during automatic approach
2. autopilot disengagement.
If the command speed changes to 0.84 Mach under either condition; disconnect
the autothrottle, push the IAS/MACH Select Switch to change the IAS/MACH
Window display to IAS, then set desired speed in the IAS/MACH Window. After
resetting speed, the autothrottle may be reconnected.
Administrative Information
Insert this bulletin behind the Bulletin Record page in Volume 1 of your
Operations Manual. Amend the Bulletin Record to show bulletin ILF2-33(R2) IN
EFFECT (IE).
Page 3 of 4
Operations Manual Bulletin No. ILF2-33(R2), Dated April 1, 1999 (continued)
This Operations Manual Bulletin will be cancelled after Boeing is notified all
affected airplanes in your fleet have been modified by Service Bulletin 747-
22A2214. If you do not plan to modify all your airplanes and would like to have
the contents of this bulletin incorporated in your OperationsManual, please advise
Boeing accordingly. Please send all correspondence regarding OperationsManual
Bulletin status to one of the following addresses:
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
Page 4 of 4
Operations Manual Bulletin No. ILF2-33(R2), Dated April 1, 1999 (continued)
Intentionally
Blank
CS3 - 2556 Page 1 of 2
Sect Name Section Name
Operations Manual Bulletin
for
The Boeing Company
Seattle, Washington 98124-2207
International Lease Finance Corp.
Number: ILF2-34(R2)
Date: April 1, 1999
Document Effectivity: D6-30151-425
Subject: EARLY VNAV DESCENT AND ERRONEOUS FMC FUEL
PREDICTIONS
Reason: To advise flight crews of erroneous FMC fuel predictions when VNAV
descent is initiated using the FMS-CDU DESCEND NOW prompt.
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.
Revised for administrative purposes.
Background Information
Boeing has received operator reports of FMC destination fuel predictions
increasing as much as 8000 pounds (3600 kgs) during VNAV descent to an
intermediate cruise altitude. In the documented instances, flight crews initiated
descent with the DES NOW prompt approximately 300 nm from destination.
The FMC changes to VNAV descent phase at the Top of Descent (T/D). With
MCP altitude set for descent, the autothrottle sets idle thrust for descent on the
VNAV path.
The DES NOW prompt, displayed at 6R on the inactive VNAV Descent page,
allows the flight crew to descend early. With MCP altitude set for descent, the
autothrottle adjusts thrust to descend at approximately 1250 fpm. If VNAV path is
captured, the autothrottle sets idle thrust to continue descent on VNAV path.
With the VNAV descent phase active, the FMC computes destination fuel
assuming idle thrust on the VNAV path. Actual fuel flow using DES NOW is
greater than idle fuel flow used for FMC fuel computations. As a result, early
descent when more than 50 nm from T/D introduces a fuel computation error. The
error increases with distance from T/D when descent is initiated.
Page 2 of 2
Operations Manual Bulletin No. ILF2-34(R2), Dated April 1, 1999 (continued)
Operating Instructions
Perform a cruise descent for descent to intermediate altitudes when more than 50
nm from T/D. During cruise descent the FMC computes a new T/D for the new
cruise altitude and accurate destination fuel predictions.
Always cross-check FMC fuel predictions with flight plan data.
Administrative Information
Insert this bulletin behind the Bulletin Record page in Volume 1 of your
　
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