Boeing Bulletins

GEN-12 : Packs Off Takeoff

1 June 2009

Effectivity

Please refer to source document.

Reason

This bulletin provides information informing flight crews of an interim procedure to prevent possible jamming of the outflow valve during a packs off takeoff. The Packs Off Takeoff supplementary normal procedure now incorporates this bulletin.

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

There have been a few reports of uncontrollable cabin pressurization when the packs were turned on following a packs off takeoff, with subsequent inability to depressurize the airplane normally after landing. This has sometimes resulted in inability to open the cabin doors for several minutes. Boeing has verified that it is possible for the outflow valve to jam in the closed position when the airplane is configured for a packs off takeoff. This can be prevented by using the manual system to position the outflow valve approximately three-quarters open prior to takeoff.

Operating Instructions

If a packs off takeoff is desired, accomplish the “Packs Off Takeoff” supplementary normal procedure. This procedure incorporates the interim steps necessary until the system is modified.

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 Boeing Service Letter SL 767-21-047C and Allied Signal Service Bulletins 2117388-21-2655 and 606832-21-2661.