The bleed ducts arent measured at the packs if my memory serves me correct. I think it is just downline from the engine. JackColwill

Disregard, I read the previous statement incorrectly.

Could you clarify that Robert? If memory serves me correctly, isn't the proper procedure on a 737 to kill the engine bleeds and power the packs via the APU? In theory the packs should stay on, and the bleed ducts won't over pressurize. Also, wouldn't turning EAI on kill any benefit you gained from turning the packs off? IIRC EAI increases EGT and fuel flow due to running warmer air through the engine.

I assume the Apu is only used for engine start and emergency situations, in order to extend the life of the APU. (i don't see why u need to run the APU if the engines are providing enough bleed pressure to run the packs and combustion cycle) secondly Robert was referring to what would happen if you did a Pack off take off and there is no need too. Boeing engines are so efficient that the duct lines can become over pressurized and trigger a fault on the overhead and pilots usually cycle Nacelle AI as a quick way to eliminate the built up pressure..Jamal Pratt