Question for 747-400 drivers

[hugh flung_dung]

I was stuck in the back of a BA 747-400 at Toronto this weekend when (we were told) the APU battery failed through overtemp just before the engines were due to be started. During the (nearly) 4 hours it took to get a replacement the Pax were kept on board with minimal air-con, a ground temperature of 29 deg and no food - pretty unpleasant!

Why wouldn't it have been possible to use Ground Power to either start the APU, start an engine or provide galley power?
or external AirCon carts?
or to off-load the pax (the air bridge was still in place)?

HFD

[Carnage Matey!]

I suspect the battery is an essential part of the APU system for fire protection reasons so no battery means no APU operation. No APU means you can't start the engines unless you get an air starter, which will also take time and require you to keep the area surrounding the aircraft clear when the engine is running, thus increasing the delay in fixing the APU. GPUs generally don't provide enough power to run the ovens in the galley, that tends to cause them to fail, plus do you really want ovens on when its already too hot . Starting an engine to cool the cabin has been done before, but it requires the agreement of the airport authorities and may not be permitted at noise sensitive airports. Can't say I've ever seen an external aircon cart. Normally its just preconditioned air which may or may not be available on any given stand. Disembarking the pax means an even bigger delay as you can guarantee in four hours time they won't all be there any more when you need them to get back. My suspiscion, as this is the way things normally go, is that the crew were told it would be a short delay which then overran considerably whilst being told "just 10 more minutes Guvnor".

[Thunderbug]

HFD

I think that Carnage Matey has hit it on the head with "just 10 more minutes". The engineers work miracles but timings can be imprecise at best. Had they known it would be 3.5 hrs they may have done the meal service and then let you all sleep for the flight. Returning passengers to the lounge is a last option as passengers tend to disappear and create further problems when reboarding happens!

There is no minimal air conditioning - it is either on or not - I'm certain that YYZ has ground conditioned air - but zone E (the back) of a 744 is really difficult to keep cool on the ground. Lots of sweaty punters and lots of IFE all steaming up the cabin. The only worse place for heat is the Flight Deck! Even with the 4 wing mounted Rolls Royce air conditioning units it can take over an hour to cool the aircraft. In your case they could not even start one as they had engineers working on the aircraft.

The aircraft can go without a working APU, but the aircraft needs the APU battery and APU battery charger as they are vital backup components for the aircraft electrical system. I note that to get you going they changed the charger and battery on your aircraft by borrowing parts from Air Canada.

It won't have made your wait any more confortable but I hope the explanation helps.

T'bug :ok:

[Intruder]

There is no minimal air conditioning - it is either on or not
Not quite...

There are 3 A/C packs on the 744, and they need a lot of air from either the APU or the engines. Though it is technically allowable to run all 3 packs on the APU, in many airplanes either the APU or 1 pack will trip off if it is attempted. Therefore, a 2-pack limit is often the realistic limit.

Also, ground A/C might be available, but not in the quantity required to cool a 744. There are connectors for 2 A/C ground hoses, but there may not be 2 carts or 2 supply hoses from the jetway supply. Also, I have been in a couple places where the airflow and/or temp output from an A/C cart is marginal.

So, "minimal" A/C is certainly a possibility, especially from the pax viewpoint...

[Capt Fathom]

Though it is technically allowable to run all 3 packs on the APU, in many airplanes either the APU or 1 pack will trip off if it is attempted. Therefore, a 2-pack limit is often the realistic limit.

Never heard that one before!! :confused:

[targaman]

I guess the learning curve never stops, eh?..................Until your brain dead! Lol

Chok Dee

[Thunderbug]

Intruder

The -400s that I work on certainly have no problems with the APUs powering 3 packs. There is a recommendation to operate only 2 packs on the ground in humid conditions to avoid Steam/mist coming from the vents.

Certainly with ground conditioned air you get what you are given. Some are better than others.

T'bug

[Intruder]

We have no FHB limit on running all 3, but I have been told by several of our mechanics that APU shutdowns have been caused by attempting to run all 3. Granted, the APU may be marginal or bad to begin with, but it has happened to me. Our unofficial SOP is to run #1 and #3 on the ground.

[hugh flung_dung]

Thanks for the info.
In practice it felt as if the packs were being cycled as there were periods of slight cooling and periods of none.

Forgive my ignorance but why isn't it possible to run an engine whilst the APU charger and battery are being replaced?

Maybe it would be better for the customer if tech delays at the gate were dealt with differently. Something like:
- confident can be fixed in 30 mins: brief pax, go ASAP
- likely to take 30-60 mins: plan for 60 min delay (feed if appropriate, etc)
- likely to be more than 60 mins: offload pax to lounge (fence-off area to keep control).
- maybe more specific action gates
... the current system is bl**dy annoying when you're on the receiving end.

I guess instructing is a lot easier than dealing with 400 p*ssed pax, or being one of them!

HFD

[matkat]

Forgive my ignorance but why isn't it possible to run an engine whilst the APU charger and battery are being replaced?

Because You would be reconnecting Them to a live power feed I for one would not want to be anywhere near Them if it was attempted.

[Intruder]

Maybe it would be better for the customer if tech delays at the gate were dealt with differently. Something like:
That's beyond the control of the crews and maintenance folks. You need to talk with Customer [Dis]Service at the airline about those policies!