Originally Posted by NuGuy

Heyas,

Regarding the packs w/ external power thing...that is a 727 thing only.

The 727 had nothing automatic at all. Even if the APU was running, you had manually connect the generator if external power dropped off. If you were using the APU to run the packs off the bleed, and external power for electrics, if the external power dropped off, the pack fans would stop, and you'd smoke the packs before they tripped off. The idea behind "don't split power" was to prevent this from happening.

The DC-9 has pneumatic flow sensors to check if the pack fans are running. If the fans stop, the system will shut off bleed air to the packs. So this issue isn't a concern on the -9.

Nu