Boeing Bulletins

GEN-15 : APU Automatic Shutdown At High Altitude

11 April 1996

Effectivity

Please refer to source document.

Reason

This bulletin provides flight crews with a modified APU Fault procedure for restarting the APU after an automatic shutdown at high altitude.

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

A recent modification to the APU has been found to cause a possible automatic shutdown of the APU. Automatic shutdown of the APU is indicated by the APU FAULT advisory message on EICAS and illumination of the APU FAULT Light.

Investigations by both Boeing and AlliedSignal have revealed that a new APU Gearbox Shutoff Valve, PN 3616848-1, can cause the automatic shutdown. The PN 3616848-1 valve has been installed on NC074 during production at Boeing and is installed on other airplanes if AlliedSignal Service Bulletin GTCP331-49- 7147 has been incorporated.

It has been found that the APU, on airplanes with the PN 3616848-1 valve, can be restarted and will operate normally at or below 35,000 feet.

Older airplanes with a previously installed valve, PN3289514-1, are not experiencing automatic APU shutdowns.

Testing has confirmed that a PN 3616848-2 configuration of the valve corrects the shutdown problem. AlliedSignal Service Bulletin GTCP331-49-7263 provides instructions for replacing the PN 3616848-1 valve with the -2 valve.

Operating Instructions

If an automatic shutdown of the APU occurs, accomplish the APU Fault procedure.

The APU Fault procedure has been modified to instruct descending to 35,000 feet or below if APU operation is required.

Administrative Information (Extract)

This Operations Manual Bulletin will be canceled after Boeing is notified that all affected airplanes in the operators fleet have been modified by AlliedSignal Service Bulletin GTCP331-49-7263.