CX Flyboy
Posts: 6007
Joined: Sun Dec 26, 1999 6:10 pm

Packs Off One At A Time.

Fri Apr 28, 2000 11:19 am

In the 747-400, before start, you turn on one pump and another to aux, fuel pumps on etc etc... When you get to packs, you switch one off, then wait about 5-10 seconds then switch the second off. I know it's due to pressure, but what damage are you exactly risking if you turn two packs off at the same time?

Curious. Any answers appreciated.

Colin.
 
airbuspilot
Posts: 382
Joined: Sat Apr 22, 2000 8:47 pm

RE: Packs Off One At A Time.

Fri Apr 28, 2000 6:11 pm

The danger by doing that is that, when switching both packs off you might have a huge pressure surge in the cabin which is not really comfortable for the pax.
Thats the only reason
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Packs Off One At A Time.

Sat Apr 29, 2000 10:09 am

You won't get a press surge in the cabin as the outflow valves will be full open. What you are preventing is press surge in the opposite diection and stalling the APU.
 
v1rot8
Posts: 6
Joined: Sat Sep 19, 2015 8:48 am

RE: Packs Off One At A Time.

Sat Apr 29, 2000 11:37 pm

I assume that this practice is only done on the 400's because it doesn't matter on the 100/200.
ragards
 
Guest

RE: Packs Off One At A Time.

Sun Apr 30, 2000 12:33 am

VC-10 is correct, the problem is potential APU compressor stall. The reason the procedure is effective to the -400 only is the -400 has a different APU. More air was needed for auto-start and airconditioning management via automatic controls.
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: Packs Off One At A Time.

Sun Apr 30, 2000 1:49 am

I believe it is good practice to apply the procedure to any jet a/c to minimise the chances of Hot or Hung starts.

In fact the A320/340 will automatically shut down the packs as soon as you select 'start' on the Start Master Switch.
 
CX Flyboy
Posts: 6007
Joined: Sun Dec 26, 1999 6:10 pm

RE: Packs Off One At A Time.

Sun Apr 30, 2000 11:53 am

Thanks for the answers - interesting indeed.

The airbus seems to have a lot of goodies that the ageing -400 does not.
To change the topic slightly, we are finally going to get autostart fitted on our -400s just like BA does. No more frantic monitoring during start.....now if only we can get electric seats fitted.....and where the hell are our headrests?

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