The Boeing Company Seattle, Washington 98124-2207
737
Number: ILF-29 Date: May 12, 2004 Document Effectivity:
Subject: FMC Arc Leg Sequencing Anomaly
Reason: This bulletin informs flight crews of a problem reported in the U10
series FMC.
Information in this Flight Crew Operations Manual (FCOM) 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 recently discovered a FMC U10 Series problem associated with sequencing waypoints with either DME Arcs to a Fix (AF legs) or Constant Radius to a Fix (RF legs). This problem only can occur if two sequential AF legs are in the route whereas this problem may occur with only one RF leg in the route.
An AF leg or RF leg is used to create an arcing route between waypoints. On the LEGS page, arc legs are identified by title containing the arc distance in nautical miles (7.3) followed by the letter L (left) or R (right), for example 7.3 L or 10.4 R. Examples of sequential DME arcs can be found on Jeppesen charts for KYKM, Yakima Washington USA, 13-1, VOR DME or GPS Rwy 27; MGGT, Guatemala, 11-3, ILS DME Arc Rwy 01; EGBB, Birmingham, UK, 11-1, ILS DME Rwy 15. The recommended method of identifying routes with DME arcs is to use the published charts as well as the FMC LEGS page.
RF legs are only used by a few operators who have tailored navigation databases associated with very low RNP operations.
If this problem occurs, the FMC does not properly sequence the waypoint at the termination of the arc and continues to provide lateral guidance commands to continue flying the arc radius. The route shown on the HSI map is not changed
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Flight Crew Operations Manual Bulletin No. ILF-29,dated May 12, 2004 (continued)
and appears normal but the airplane will begin deviating from the magenta flight path since lateral guidance continues to follow the arc radius. Lab testing indicates that during this condition, LNAV will remain engaged. If Navigation Performance Scales (NPS) are installed, they provide an erroneous display of flight technical error because lateral deviation is based on continuing to follow the arc rather than the displayed magenta path. This problem has been reported during a non-revenue flight test and during flight simulator testing. Boeing is not aware of any in-service reports of this problem.
A remedy for this problem is planned to be incorporated in the next FMC software update, U10.5A. As a result, we plan to delay the previously scheduled certification date of U10.5A from May 2004 to approximately June 2004.
Operating Instructions
Boeing recommends that in either IMC or VMC conditions, flight crews monitor routes with DME arcs (AF legs) to insure the airplane follows the published route. Until a remedy has been incorporated, we recommend flight crews not use Constant Radius Arcs (RF legs) unless in VMC.
Administrative Information
Insert this bulletin behind the FCOM Bulletin Record Page in Volume 1 of your FCOM. Amend the FCOM Bulletin Record Page to show Bulletin ILF-29 "IN EFFECT" (IE).
This condition is temporary and will be corrected in FMC Update U10.5A which is expected to be released approximately June 2004. This bulletin will be cancelled after Boeing is notified that all affected airplanes in your fleet have been updated to FMC software U10.5A.
Please send all correspondence regarding FCOM bulletin status to one of the
following addresses:
Mailing Address: Manager 737, Flight Technical Integration & Data Boeing Commercial Airplane Group P. O. Box 3707 MS 20-89 Seattle, WA 98124-2207 USA
Fax Number: Telex: SITA: E-MAIL: (206) 662-7812 329430 Station 627 LKEBO7X FTID@Boeing.com
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737 Operations Manual
Operating Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .L.10.1
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.10.1 Airplane General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.10.1 Operational Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.10.1 Non–AFM Operational Information . . . . . . . . . . . . . . . . . . . . L.10.1 Weight Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.10.2 Air Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.10.9 Anti–Ice, Rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.10.10 Autopilot/Flight Director System . . . . . . . . . . . . . . . . . . . . . . . . L.10.10 Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L.10.10
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