BA G-BNLG questions...

[Self Loading Freight]

I was on this a/c on Sunday, flying back from SFO to LHR, and had the good luck to get seat 28B right next to the left-hand overwing emergency exit. Enough legroom for a giraffe. Joy.. .. .But it was an odd flight. No aircon on the ground with the engines off, and the engines weren't started until well after pushback; likewise back at LHR, where we spent 45 minutes hanging around after landing while they tried to find a gate, then get the a/c on the gate moved, then waiting for somebody to come and ground the a/c before we could disembark. Finally, the captain got on the PA and said that he'd have to turn the engines off to help grounding before we could get off, and that the lights would dim. They didn't just dim, they went off completely: this is the first time I've been on an in-service a/c full of passengers when it's gone completely dead. A very eerie sensation. . .. .What would cause this? I *think* the captain said that the APU was unservicable, but in that case would it be safe to fly? And why were the engines off at the beginning -- fuel conservation?. .. .I have to say, looking at the aircraft reg stuck to the side of the emergency exit (odd place for it), I started to think of the a/c as Getting Back No Longer Guaranteed.... .. .R

[Lunar Landing]

As far as i know, the APU is used for start up, but switched off once flying or taxing ready for takeoff. Why the lights dimmed i dont know, but do know the APU is off for flight. Well, thats what the PS1 (precision simulator) tells me, and that cost 190 quid!!. .. .Smooth skies.... .Dan <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />

[moleslayer]

Sounds like a classic duff APU scenario,a regular occurrence.The APU provides air conditioning & electrical power until the engines are started.. .On arrival a ground power unit is plugged-in to power the electrics, however if the ground crew can't get one 'toute-de-suite' then the only course of action is to shut down the engines and plunge everyone into darkness.The 'dim' emergency standby lighting then automatically illuminates.. .Nothing to be concerned about, just a bit disconcerting.(did I really mean to say that?) <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />. . . . <small>[ 05 March 2002, 13:22: Message edited by: moleslayer ]</small>

[Jet II]

Definatly a U/S APU - the APU supplies pneumatics to run the aircon when no engines operating and same for electrics. Surprised that no external aircon supplied at SFO whilst boarding, most ground handling companies have carts available for this precise reason. . .. .Normal procedure on arrival is to keep at least one engine running (to provide electrics) whilst ground staff plug-in external power.. .. .APU's are used in flight if one of the main electrical generation systems is inop - just have to load more fuel to compensate for extra fuel burn.

[whats_it_doing_now?]

Just to add.... .. .The engines wouldn't have been started until well after push back because you have to crossbleed the air to start the engine when the apu is u/s. Haven't flown a 74, but i assume its similar to most aircraft. You start one engine on stand using air from an external source, then once pushback is completed you have to start the remaining engines using air from the one that is running. To get sufficient pressure to do this, you have to stick a touch of power on - unwise when a tug is pushing you back which is why you have to wait.. .. .Add to this the problems already mentioned and you come to realise that an APU u/s is a pain in the posterior. Sounds like yours was made worse by a lack of stands and equipment at LHR.

[Sonic Cruiser]

Have been on a few 747-400s on the ground where the lights have gone out completly. Fun for the pax, especially at 6am when it is still dark.. .Sometimes happens when APU is shut down and crew don't push the external power switch overhead or it trips out. Also had it happen when the APU has tripped out leaving no power at all.. .As for stands at EGLL bring on T5, frequently aircraft are holding somewhere waiting for stands. ATC do a fantastic job with limited space

[Captain Airclues]

SLF. .. .The normal procedure with a U/S APU is to start two engines on the gate using ground air supplies and then start the other two after pushback using air from the running engines. However, as you know, the gate area at KSFO is very congested, and it is possible that they had to start all four in a safe area.. .At weights below 300,000kgs we take-off with all three air conditioning packs on, and the APU switched off. At higher weights the APU remains running, and is used to supply air to the centre pack for air conditioning. With the APU U/S, the take-off would have been completed with all three packs running. This would have meant a 2000kgs weight penalty, but at the relatively light weight ex KSFO this would not have been a problem. The APU must be switched off by 20,000ft (usually much earlier). There is absolutely no safety implications with departing with a U/S APU.. .On arrival at the gate the procedure is to shut down #2,#3 and #4 engines, and keep #1 running until ground electrics have been established. I do not know the facts in your case, but it is possible that the captain decided that it was safer to disembark the passengers without electics (in daylight), rather than risk a groundcrew inadvertently approaching the aircraft and being injured. I'm sure that, having reached the gate the passengers were all still strapped in their seats as instructed, and he was probably aware that you were keen to get off. Full emergency lighting is available even with no engines and no ground electrics.. .I hope that this helps. E-mail me if you require any further information. .. .Airclues