Boeing Bulletins

FMC-4 : Performance Predictions Anomaly in Flight Management Computer (FMC) Product Improvement Package (PIP) and Pegasus Software Versions

1 June 2009

Effectivity

Please refer to source document.

Reason

To inform flight crews of a performance prediction anomaly on FMC-PIP and Pegasus-FMC software versions.

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.

Background Information

Boeing has confirmed operator reports regarding erroneous performance predictions following execution of the ABEAM PTS function on the LEGS page of the FMC-Product Improvement Package (PIP) and Pegasus-FMC software versions. When OAT values have been previously entered in the ALT/OAT field of line-select key 5R on a waypoint WIND page, and the ABEAM PTS function is subsequently selected after a "direct-to" flight plan modification, the OAT value on the WIND page erroneously changes to 0-degrees. After execution, fuel predictions are erroneously recalculated based upon 0-degrees instead of the previously entered value for the respective cruise altitude. Operators have reported display of the INSUFFICIENT FUEL alert-level scratch pad message with the fuel prediction values being much lower than originally planned. Additionally, there are no flight deck annunciations or alerts to indicate an OAT value on the WIND page has erroneously changed.

This Flight Crew Operations Manual Bulletin is only applicable to the FMC Product Improvement Package (PIP) and Pegasus-FMC software versions. Previous FMC software versions do not include the ABEAM PTS function, the ALT/OAT field entry, or individual waypoint WIND pages, and therefore, are not affected.

Operating Instructions

Following selection and prior to executing the ABEAM PTS function, verify the OAT value on the respective WIND page. If necessary, enter the airplane altitude and the indicated Static Air Temperature (SAT) value from PROGRESS page 2 into the ALT/OAT field for the next route waypoint. This OAT entry will propagate to all down-track waypoints. Following entry of the SAT value into the ALT/OAT field and execution of the route modification, the FMC fuel predictions should be near those obtained from the flight plan.

Administrative Information (Extract)

The corrective action for the anomaly described in this Flight Crew Operations Manual Bulletin is still under investigation. This bulletin will be revised to include Service Bulletin information when available.