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Operations Manual Bulletin No. ILF2-33(R2), Dated April 1, 1999 (continued)
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Operations Manual Bulletin
for
International Lease Finance Corp.
The Boeing Company Seattle, Washington 98124-2207
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. Revised for administrative purposes.
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.
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
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.
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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 Operations Manual. Amend the Bulletin Record to show bulletin ILF2-34(R2) IN EFFECT (IE).
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: Telex: (206) 662-7812 32-9430 Station 627
SITA: SEABO7X
Page 2 of 2
Operations Manual Bulletin
for
International Lease Finance Corp.
The Boeing Company Seattle, Washington 98124-2207
Number: ILF2-36(R2)
Date: April 1, 1999 Document Effectivity: D6-30151-425 Subject: ERRONEOUS ILS RECEIVER OUTPUTS Reason: To advise operators of possible erroneous outputs from the Allied Signal
“Quantum” ILS receiver. Revised for administrative purposes.
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.
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