Flight Crew Operations Manual Bulletin
for
The Boeing Company Seattle, Washington 98124-2207
737
Number: SHZ-12 R1 Date: March 01, 1999 Document Effectivity:
Subject: FMC Software Restart Anomaly
Reason: This is a reissue of SHZ-12, dated December 1, 1998, which informed flight crews of potential FMC software restarts caused by certain CDU inputs during flight. The purpose of this reissue is to add Service Bulletin information.
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 confirmed an airline report of FMC anomalies which can cause software restarts during flight. When in the descent phase of flight, if the flight crew EXECutes a change to the flight plan on the ACT RTE LEGS or ACT RTE page and then presses the DES key to display the DES page before predictions have completed processing, an FMC internal program fault will occur causing an FMC “software restart.” The FMC navigation function does not correctly recover from the program fault causing a variety of misleading cockpit displays and lateral guidance anomalies until the correction is complete. In airplanes with dual FMCs, the restart can occur in one or both FMCs. In airplanes with a single FMC, the correction of the program fault may take up to 8 minutes.
Laboratory testing has verified that these anomalies are limited to FMCs loaded with software version U10.2. These anomalies can cause a significant increase in pilot workload and have the potential to degrade the flight crew's situational awareness. LNAV guidance can be unreliable, the MAP display can be oriented along an erroneous track and a large erroneous wind can be displayed on the MAP and CDU. The software will be revised as soon as possible. The following specific flight deck effects are indications of a software restart:
Flight Crew Operations Manual Bulletin No. SHZ-12 R1, dated March 01, 1999 (continued)
For single FMC installations:
.
VTK flag, if navigation display is in MAP or CTR MAP mode
.
Amber FMC light on pilots’ instrument panels
.
LNAV and VNAV disconnect
.
CDU installation - “FMC” displayed on CDU for approximately 5 seconds
.
MCDU installation - MCDU display reverts to MENU page, initially without “<FMC” prompt
For dual FMC installations: Left FMC restart indications:
.
VTK flag if Captain's navigation display is in MAP or CTR MAP mode
.
Amber FMC light on pilots’ instrument panels
.
LNAV and VNAV disconnect if FCC A is in CMD or is the master F/D
.
CDU installation - “FMC” displayed on CDU for approximately 5 seconds
.
MCDU installation - MCDU display reverts to MENU page, initially without “<FMC” prompt
Right FMC restart indications:
.
VTK flag if First Officer's navigation display is in MAP or CTR MAP mode
.
Momentary amber FMC light on pilots’ instrument panels (displayed for at least 4 seconds)
.
LNAV and VNAV disconnect if FCC B is in CMD or is the master F/D
.
FMC CDU message “SINGLE FMC OPERATION”, which may clear
after 4 seconds Service Bulletin 737-34A1502, released December 17, 1998, provides information on the U10.2A software upgrade that fixes the anomaly.
Operating Instructions
While in the descent phase of flight, flight crews should not make modifications to the flight plan on the ACT RTE LEGS or ACT RTE page and then press the DES key before predictions have completed processing. Approximately 10 seconds elapsed time after EXECuting the modification or display of destination ETA on the CDU PROGRESS 1/3 page indicates processing completion.
If a program fault software restart occurs, LNAV and VNAV are not available. Use conventional means of navigation until the restart is complete and navigation indications have returned to normal.
Flight Crew Operations Manual Bulletin No. SHZ-12 R1, dated March 01, 1999 (continued)
The following procedures may help speed the recovery from a program fault: For single FMC equipped airplanes:
.
The FMC will be unusable for 6 - 8 minutes.
.
When the FMC CDU POS REF 2/3 page indicates an FMC groundspeed (GS) of 80 kts or greater, a position shift to an IRS position should be executed on the POS SHIFT 3/3 page.
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