Pressure, Air Conditoning & Weight ?

Shuttie · Post by **Shuttie** » 05 Nov 2006, 13:53

A friend of mine took the United Airlines flight to Washington DC on Thursday.
Before they took off, the passengers were warned that they may feel a change in pressure before during take off.
The reason given was related to the air conditioning not being run, due to weight limitations ?

Can anyone explain the relationship between pressure, air conditioning and weight ?

bits44 · Post by **bits44** » 05 Nov 2006, 15:13

That's a common practice with high load factors, The AC System operates off the bleed air system from the engines, turning the AC off during take off allows the engines to produce more power, a vital safety factor.

The AC would be turned back on soon after climb out.

KT

EBAW_flyer · Post by **EBAW_flyer** » 05 Nov 2006, 19:44

Actually, with some companies every T/O is done with pressurisation off; after thrust reduction, it is set on again.

pilatus · Post by **pilatus** » 06 Nov 2006, 11:26

I thought that passenger airlines use the APU during TO for pressurisation and airco.
We, in the cargo, put th APU off before TO and also the airco/press. till after TO.
Maybe they had a broken APU?

Greetz,

DiverDriver

EBAW_flyer · Post by **EBAW_flyer** » 06 Nov 2006, 16:32

With TCW, the standard procedure is a pack OFF T/O, so no APU either.

Bracebrace · Post by **Bracebrace** » 07 Nov 2006, 11:21

It all depends on the aircraft specific and company procedures. For the 737, I should check it but I don't think we have packs off procedures. We do have a bleeds off takeoff procedure which we can use when we need the performance. Normally the APU will remain running and bleed air from the APU will be used to supply the packs. So there's no real problem for the passengers.

However, in case the APU is inop, there is no pressurization on takeoff and you have the "pressure bump" problem when resetting the bleed supply system.