Curious ... AIX 738 packs OFF till airborne ?

IndAir967 · 15th Apr 2010, 12:09

Recently was doing an off-duty on Air India Express B738.

Wondering if its your SOP to keep your PACKS OFF until airborne ?
Any AIX or may be any 738 deck guys around to enlighten..
Do u guys monitor the cabin temp during surface movement ?
I mean it was freakin hot and your RECIRC Fans are useless..
OAT must have been what 40 C

I mean in my SOP (A320) its Packs OFF prior to line up then once airborne
and CLB thrust is annunciated then Pack 1 + 1 min + Pack 2 .. that way the pax are much comfortable..

Thanks
IndAir967

iflytb20 · 16th Apr 2010, 04:29

Some of our acft are having this problem on the ground. The engines at IDLE don't produce enough bleed pressure to cool the cabin effectively if the OAT is > +30 C. Also had a few acft getting AOGed due to this. To prevent this we try and taxi [where ever possible] with a slightly higher thrust. Sorry to hear you had a bad experience.

Cheers

Centaurus · 16th Apr 2010, 14:03

Quote:

To prevent this we try and taxi [where ever possible] with a slightly higher thrust.

Depends on how you define "slightly". Any thrust higher than needed while taxiing is against the Boeing warning that dragging the brakes in order to keep taxi speeds down (if more than idle thrust is being used for taxiing) will cause brake over-heating and potential for wheel well fire warning after the landing gear is retracted after lift off. I think most passengers would prefer to have a hotter cabin than a fire in the air.

iflytb20 · 16th Apr 2010, 15:31

@Centaurus
Normal Taxi is with IDLE thrust [about 21% N1]. In the acft with bleed problem, we use around 26-27% N1. And we DON'T use brakes with thrust. We only keep this higher thrust on long straight taxiways. Since our usual TOW is around 72T, 27% N1 helps us maintain about 22-25 knots while taxing.

Cheers

alienpilot · 20th Apr 2010, 09:21

Using higher N1 is not recommended for the reason mentioned in earlier post and it makes very little difference in any case.

The problem with air condtioning is usually due to clogging of heat exchanger, which needs cleaning or some other reason causing reduced bleed pressure. There are a few aeroplanes that have this problem and its really miserable for pax. Airline needs to be particular with engineering dept to pay attention to this important aspect in searing heat.

Packs are always on except for the duration of start.

NGFellow · 20th Apr 2010, 17:39

Why not just use the APU to feed the PACKS after start and during taxi. Reconfigure the bleeds prior to Takeoff? The APU will do a better job than the engines at idle power, and there is no need to use a higher power setting.

Flaperon777 · 21st Apr 2010, 12:49

Isolation open,both packs on 'High'. Problem solved...

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