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Packs Off One At A Time.  
User currently offlineCX flyboy From Hong Kong, joined Dec 1999, 6693 posts, RR: 55
Posted (15 years 2 days 16 hours ago) and read 1376 times:

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.


6 replies: All unread, jump to last
User currently offlineAirbuspilot From Belgium, joined Apr 2000, 416 posts, RR: 2
Reply 1, posted (15 years 2 days 9 hours ago) and read 1205 times:

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

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3719 posts, RR: 33
Reply 2, posted (15 years 1 day 17 hours ago) and read 1162 times:
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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.

User currently offlineV1ROT8 From , joined Dec 1969, posts, RR:
Reply 3, posted (15 years 1 day 4 hours ago) and read 1130 times:

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

User currently offlineDonm From , joined Dec 1969, posts, RR:
Reply 4, posted (15 years 1 day 3 hours ago) and read 1132 times:

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.

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3719 posts, RR: 33
Reply 5, posted (15 years 1 day 2 hours ago) and read 1121 times:
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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.

User currently offlineCX flyboy From Hong Kong, joined Dec 1999, 6693 posts, RR: 55
Reply 6, posted (15 years 16 hours ago) and read 1105 times:

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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