Boeing Bulletins

FMC-2 : Consecutive Conditional Altitude Waypoints Map Anomaly

20 November 1995

Effectivity

Please refer to source document.

Reason

To inform flight crews of an HSI Map display anomaly associated with routes containing two consecutive conditional altitude waypoints.

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

During flight test, a Boeing flight crew experienced an HSI Map display anomaly. Simulator and lab tests show that when two consecutive conditional altitude waypoints exist in a procedure, the Map display of the magenta line does not reflect the intended path on the active leg for the conditional altitude waypoint. The displayed magenta line may erroneously indicate a turn prior to the airplane satisfying the required altitude for the turn. Conditional altitude waypoints are depicted as a small circle along with the altitude on the HSI Map display and their location depends on the airplane satisfying the altitude associated with the leg.

Consecutive conditional altitude waypoints may appear in Standard Instrument Departures (SID) and Missed Approach procedures and are automatically entered into the route when a procedure is selected from the FMC DEPARTURES or ARRIVALS page.

Procedures which use this combination of two consecutive altitude waypoints usually require a climb to a specified altitude followed by a small turn to intercept a VOR radial while climbing to a higher altitude. Approximately 400 procedures worldwide are affected by this anomaly.

Honeywell and Boeing are investigating this anomaly.

The typical HSI Map display and corresponding RTE LEGS page display for conditional altitude waypoints are shown below:

Operating Instructions

When flying a SID or missed approach procedure containing consecutive conditional altitude waypoints, the active route shown on the HSI Map is incorrect; however, LNAV guidance is reliable and may be flown using either the flight director or autopilot. Monitor LNAV progress and insure all altitudes and turn points are consistent with the procedure and available raw data.

Three different vendors (Jeppesen, Swissair and Racal) supply navigation data bases for the FMC. Currently affected procedures for each vendor’s navigation data base are contained in the original bulletin and are not reissued with this bulletin. To determine which vendor supplies your data base, check the Navigation Data Line on the FMC IDENT page. The navigation data base identifier begins with a three letter code. Use the attached Navigation Data Base vs. Vendor Reference Table (A) to determine the vendor associated with the three letter navigation data base identifier. Then locate the attached vendor tables (B1, B2 and B3) to determine the affected procedures.

Operations Manual Bulletin Attachment Consecutive Conditional Altitude Waypoints Map Anomaly

Administrative Information (Extract)

This anomaly will be corrected by Boeing Service Bulletin 757-34-0181. Other FMC’s are corrected by Boeing Service Bulletin 757-34-0192 or 757-34-0210 or 757-34-0212. Refer to individual Service Bulletin for applicability.