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FLEX1978

747-400 loses all 4 Generators

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Rob,The incident your refer to with reference to an encounter with volcanic ash occured on 24 Jun 1982 to a BA 742 G-BDXH 'City of Edinburgh' flying south of Jakarta on its way from KUL to PTH.Unlike this most recent event the aircraft did not suffer a full-electrical failure as you suggest mainly due to the fact that despite 4 flamed-out engines there was sufficient airflow to keep them 'windmilling'; this was in addition to the successful implementation of the 'Loss of All Generator Drill' from the QRH. Luckilly the windmilling engines were also able to supply sufficient power to the hydralics systems to keep the aircraft flyable.Kind RegardsSteve Bell

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Yeah I read about G-BDXH It's now gathering dust somewhere in the south of England. I was just thinking, whats the chance of loseing all four Gens or Engines at the same time. As far as im aware those are the only two events on a 747Rob

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Well it can happen. You may have not have seen this from Australian Aviation:QANTAS 747 LOSES POWER IN FLIGHT NEAR BANGKOK: A Qantas 747-400 en route from London to Bangkok lost all main electrical power while on descent into Bangkok on January 8.The aircraft, operating QF2 and carrying 344 passengers, reportedly operated the final 15 minutes of its flight on backup battery power only after water from a galley contaminated the main electrical racks shorting out all of the aircraft's AC power generators. The backup batteries have a capacity to provide basic cockpit instrumentation, communications and emergency lighting for between 60 and 90 minutes. The aircraft landed safely.Qantas and the ATSB have confirmed an investigation into the incident is underway in conjunction with CASA, Boeing and Thai authorities.Neil

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In case you ever encounter volcanic ash and you see arcing on the windshield or a failing generator...start off by making a 180 degree turn back followed by disconnecting the Auto-throttle or A/Thr,put on your oxygen masks,anti-ice on (Total) set your pack flow to "HI" and start your APU. (Based on the Airbus recommended procedures).-Navneet ReddyA320 F/Owww.airdeccan.net

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"The backup batteries have a capacity to provide basic cockpit instrumentation, communications and emergency lighting for between 60 and 90 minutes."The Boeing Maintenance Manual says only 30 minutes. i.e. guaranteed. The batteries would have to be in very good condition to last that long.I laugh when they say "basic cockpit instrumentation".... All the Captain's screens would be ok, including the Upper EICAS. They would have full FMC guidance. 2 IRU systems would be operating (the Centre IRU stops after 5 minutes on battery power). Left VHF, Left ILS, etc... would all be working.They would need to fly the plane manually, however (no A/P).For fun... Try it in PMDG... Just deselect the GCB's.The full details on the incident are not in yet. There are some pretty wild accusations and lots of misinformation being spread on internet forums (including supposedly expert forums such as PPRuNe). Some newspapers are claiming they got some of their information from a Qantas Engineer... If so.. he should hand back his licence.... He hasn't a clue what he's talking about (e.g. suggesting that the APU generators could have been used as a backup). You can't even start the APU in the air.Cheers.Q>

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I do laugh when I read some of the newspaper reports here in England... They would proberbly add "The Captain managed to enable the backup Flux invertor just in time, narowly missing a 650000 ton Supertanker.Rob

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Most if not all APU's can be started in the air for reasons much like this. So they could in fact be used as a backup. But Im guessing in the 747 the AC GEN would be connected the the damaged racks so wouldnt have been much help in this case. Im not a 747 LAME but I have experiance on other Boeing aircraft.Its situations like this that I find it bizzare that a RAT (Ram Air Turbine) wasnt built into the 747! But on the other hand the chances of loosing PWR from all 4 GENs in flight is very remote.

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Hey Ryan, THe 747-400 Apu cannot be started in flight. However you can perform a Packs to APU departure and have APU running to around 20000ft (not 100% sure on the Alt) Rob

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"But Im guessing in the 747 the AC GEN would be connected the the damaged racks so wouldnt have been much help in this case."The APU Generator control units are located on the same racks. Perhaps the weak links here are the Bus Control Units on those racks. One is essentially a slave to the other one. If the first one gets drenched, the second one probably doesn't have a clue what's going on. The Bus Control Units are the brains behind the electrical system.RAT's were originally only for hydraulic power. Newer ones, however, provide electrics and hydraulics, but how's that going to help you if you can't get that electrical supply to the busses because of electrical system control problems?Cheers.Q>

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You can start the APU on the 744 in flight by tricking the aircraft to think it's on the ground by pulling the "ground safety" CB.This of course in this particular incident would have been the wrong thing to do as it would have severely shortened the battery life but there was no way for the crew to know what the root cause of the problem were.

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The problem could have been a lot worse, if this had happened in the middle of the ocean, at night, in marginal weather, hours from land, then the situation could become critical very quickly, and very easily could end in tragedy...it has happened before.Anthony

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Would that mean the aircraft enters ground mode in flight? IE Reversers can be deployed TA Transponder and full spoilers?Rob

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"You can start the APU on the 744 in flight by tricking the aircraft to think it's on the ground by pulling the "ground safety" CB."The last time I pulled a ground safety CB on a 744 (last week), it put some systems into AIR MODE. This requires some further investigation.Even so.. with the BCU's underwater, you probably couldn't get the APU power to the busses.Cheers.Q>

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P.S. Something to consider... The Automatic control of the pressurisation outflow valves. You wouldn't want these to go to full open in cruise (as they do on the ground). Although, I hear that crew of the QF 744 went to manual pressurisation control, so it shouldn't be an issue.

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Another consideration.... With Standby Power you still have the IRU's running, providing you with position and heading information (which will feed the Captain's MAP display) and attitude and heading information (which will be provided to the PFD). The IRU's are powered by the APU Battery in the absence of main bus AC. If you were able to crank the APU starter motor (by pulling certain Air/Ground CB's), there would be an enormous drain on the APU Battery during start. How this would affect the IRS's I really can't say. If you got main bus power online, but have lost the IRU's, it's a big sacrifice. IRU attitude can be recovered with the aircraft in motion, but not position.You might be able to get both GPS's to operate with main bus power re-established, however, this probably won't be able to supply position to the MAP display with the IRU's inop. Some 744's have Multi-Mode Receivers which include GPS as well as ILS/Marker. One GPS system may even be operative under Stby Power ops, but it will only last as long as the batteries do.A complex issue indeed.Cheers.Q>

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