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B 747-400 Engines Off  
User currently offlineRadimz From Czech Republic, joined Dec 2006, 8 posts, RR: 0
Posted (7 years 3 months 3 weeks 5 days 1 hour ago) and read 6278 times:

Hello,
I have a question: what happens with the generator on a B 747-400 when the engine is shuted down due to a flameout or a engine malfunction? Can it generate power with windmilling engines?
Thanks

51 replies: All unread, showing first 25:
 
User currently offlineCFMTurboFan From Canada, joined May 2007, 41 posts, RR: 0
Reply 1, posted (7 years 3 months 3 weeks 5 days 1 hour ago) and read 6261 times:

The generator which is typically reffered to as an IDG (Intergrated Drive Generator) is mounted on an engines accessory drive gearbox. Gearboxes are driven by the HP and in some cases the IP compressor spools via a radial drive shaft to the accessory drive gearbox. The IDG is driven by the gearbox.

IDGs normally need to rotate around 7000rpm output to the internal generator (not sure if this is correct, correct me if it's not) to produce the required electrical frequency for the aircraft. This power is fed into the aircraft main buses via 4 heavy duty wires running to the IDG.

If an engine flames out, or is shut down, then it will not provide the required rotation via the gearbox to the IDG to produce the required power and therefore will not supply power.

[Edited 2007-05-24 17:36:34]

[Edited 2007-05-24 17:41:08]

User currently offline777WT From United States of America, joined Jan 2005, 875 posts, RR: 1
Reply 2, posted (7 years 3 months 3 weeks 5 days 1 hour ago) and read 6232 times:

Then if that's the case, then howcome 747's don't need RAT since 4 windmilling engines is more than enough to provide hyd power?

User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 3, posted (7 years 3 months 3 weeks 5 days ago) and read 6211 times:

Quoting 777WT (Reply 2):
Then if that's the case, then howcome 747's don't need RAT since 4 windmilling engines is more than enough to provide hyd power?

Providing windmilling hydraulic power and having the IDG work are two different things. First windmilling hydraulic will get you the pressure needed but it might not get you the volume. That is why Boeing recommends against an attempt at landing the aircraft if all engines are flamed out. You will most likely get the gear and some flaps out, but as you slow the windmilling will also be less reliable.

The IDG acts as a transmission. It provides a constant RPM range to the generator thus allowing it to operate over a very narrow volt and frequency range (115v +/-2 and 400HZ +/-5). The problem is the generators don't come on line until just about at the end of the start cycle. In a windmilling situation, you won't have even that rotation. So, no IDG.


As for no RAT, the odds of losing all 4 electrical systems is fairly remote. Even on one generator, with selective equipement off, the aircraft will fly all day.


User currently offlineZANL188 From United States of America, joined Oct 2006, 3521 posts, RR: 0
Reply 4, posted (7 years 3 months 3 weeks 5 days ago) and read 6202 times:
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Quoting PhilSquares (Reply 3):
That is why Boeing recommends against an attempt at landing the aircraft if all engines are flamed out.

 Smile

Like Boeing or the pilot has a choice in the matter.......



Legal considerations provided by: Dewey, Cheatum, and Howe
User currently offlineDH106 From United Kingdom, joined Jun 2005, 626 posts, RR: 1
Reply 5, posted (7 years 3 months 3 weeks 5 days ago) and read 6195 times:

Quoting ZANL188 (Reply 4):
Quoting PhilSquares (Reply 3):
That is why Boeing recommends against an attempt at landing the aircraft if all engines are flamed out.



Like Boeing or the pilot has a choice in the matter.......

Exactly - LOL
Next time I have a quad failure in a 747 - I must remember to stay up there until the problem's solved !!  rotfl 



...I watched c-beams glitter in the dark near the Tanhauser Gate....
User currently offlineSilverComet From Mauritius, joined Apr 2007, 85 posts, RR: 0
Reply 6, posted (7 years 3 months 3 weeks 5 days ago) and read 6173 times:

Quoting PhilSquares (Reply 3):
That is why Boeing recommends against an attempt at landing the aircraft if all engines are flamed out.

On a more serious note though, what does Boeing recommend in that situation? I imagine attempt restart, but other than that (if restart fails)?


User currently offlineArniePie From Belgium, joined Aug 2005, 1265 posts, RR: 1
Reply 7, posted (7 years 3 months 3 weeks 4 days 23 hours ago) and read 6151 times:

If you loose all engines wouldn't the APU be able to do the job?
Dumb question maybe but can't it be used in flight to power the hydraulics and give electricity?

Quoting SilverComet (Reply 6):
I imagine attempt restart, but other than that (if restart fails)?

Pray, or let all passengers drink Red bull (gives you wings!!!).



[edit post]
User currently offlineRadimz From Czech Republic, joined Dec 2006, 8 posts, RR: 0
Reply 8, posted (7 years 3 months 3 weeks 4 days 23 hours ago) and read 6141 times:

I think the APU cant be started in flight so it wouldnt supply nor electricity nor bleed air

User currently offlineDH106 From United Kingdom, joined Jun 2005, 626 posts, RR: 1
Reply 9, posted (7 years 3 months 3 weeks 4 days 23 hours ago) and read 6111 times:

Hmmm - so say, if the 'Gimli Glider' had been a 747 (i.e. run out of fuel with no hope of a restart) - what would Boeing recommend? It's clearly an envisagable circumstance.


...I watched c-beams glitter in the dark near the Tanhauser Gate....
User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 10, posted (7 years 3 months 3 weeks 4 days 23 hours ago) and read 6109 times:

Radimz

...what happens with the generator on a B 747-400....Can it generate power with windmilling engines?...

CFMTurboFan and PhilSquares have both answered your question already, but I'd just like to mention a point that follows on from what they have said.

With all four engines operating normally, but at flight idle power - for example during descent from cruise altitude - it can be harder than you might think to spot an engine failure, should an engine quietly just run down. Initially a failed engine will be indicating roughly the same EPR, EGT and Fuel Flow as the other engines, whilst they are at flight idle, there will be little or no yaw or roll affecting the aircraft and the control column will have little displacement from its normal position.

In such a situation, it is highly likely that the first EICAS warning you will get following, say, a #4 engine run-down, will be an Electrical warning, such as "ELEC DRIVE 4" or "ELEC GEN OFF 4", as the IDG drops off-line, because, as has been said, a windmilling engine will not be turning fast enough to keep its IDG on-line.

Odd though it may sound, following an electrical generator type warning, most B747 pilots will first make a quick check that the associated engine is running normally, before actioning the electrical QRH!

Best regards

Bellerophon


User currently offlineSilverComet From Mauritius, joined Apr 2007, 85 posts, RR: 0
Reply 11, posted (7 years 3 months 3 weeks 4 days 22 hours ago) and read 6059 times:

Quoting Radimz (Reply 8):
I think the APU cant be started in flight so it wouldnt supply nor electricity nor bleed air

APU can be started in flight, and deliver electricity and bleed provided it is within it's operating altitude limits.


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 12, posted (7 years 3 months 3 weeks 4 days 21 hours ago) and read 6045 times:

Quoting SilverComet (Reply 11):
APU can be started in flight

Only on the classic. On the 747-400 the APU can be left running in flight, but not started in flight.

As for a RAT, as has been stated on numerous previous threads the primary purpose of a RAT is to supply hydraulic power for flight controls. In aircraft where electrical power is also required for flight controls (e.g. FBW Airbus types) there is also a hydraulically powered generator installed. The VC10 was an exception as it had two RATs one electrical and one hydraulic.

All the 747 flight controls need is hydraulic power and the windmilling engines are enough for that. Standby electrical power is available from the battery for a limited time. So the 747 does not need a RAT.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineBoeingOnFinal From Norway, joined Apr 2006, 476 posts, RR: 0
Reply 13, posted (7 years 3 months 3 weeks 4 days 21 hours ago) and read 6029 times:

Quoting ZANL188 (Reply 4):
Quoting PhilSquares (Reply 3):
That is why Boeing recommends against an attempt at landing the aircraft if all engines are flamed out.

Smile

Like Boeing or the pilot has a choice in the matter.......

Obviously they recommend that you stay in the air until someone comes to fix the problem!



norwegianpilot.blogspot.com
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 14, posted (7 years 3 months 3 weeks 4 days 21 hours ago) and read 6015 times:

The APU on the 747-400 can't be started in flight. But if it was already running while on the ground and the aircraft takes off, it will continue running, up to a certain altitude. It can provide bleed air while in flight, but as soon as the aircraft goes into air mode, the APU generators cannot be used.


Chris



Don't blame me, I don't work here...
User currently offlineKELPkid From United States of America, joined Nov 2005, 6381 posts, RR: 3
Reply 15, posted (7 years 3 months 3 weeks 4 days 21 hours ago) and read 5992 times:

Quoting N8076U (Reply 14):
The APU on the 747-400 can't be started in flight.



Quoting PhilSquares (Reply 3):
That is why Boeing recommends against an attempt at landing the aircraft if all engines are flamed out.

Remind me never to mismanage fuel in a 747-400...  eyebrow 



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3701 posts, RR: 34
Reply 16, posted (7 years 3 months 3 weeks 4 days 20 hours ago) and read 5956 times:
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Quoting Jetlagged (Reply 12):
The VC10 was an exception as it had two RATs one electrical and one hydraulic.

The BUA '10's only had one RAT


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 17, posted (7 years 3 months 3 weeks 4 days 16 hours ago) and read 5850 times:

Quoting PhilSquares (Reply 3):

As for no RAT, the odds of losing all 4 electrical systems is fairly remote. Even on one generator, with selective equipement off, the aircraft will fly all day.

"Ladies and gentlemen, we are going to be turning off the reading lights, the entertainment system and the coffee machines. Don't panic."

Quoting DH106 (Reply 9):
Hmmm - so say, if the 'Gimli Glider' had been a 747 (i.e. run out of fuel with no hope of a restart) - what would Boeing recommend? It's clearly an envisagable circumstance.

First of all, I'm sure Captain Squares is aware of the fact that if the engines can't be restarted, eventually the aircraft will touch down whether he wants it to or not.

The Gimli Glider incident would have been one case where Boeing could recommend all it wanted. The landing would have been attempted without any engines on.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKELPkid From United States of America, joined Nov 2005, 6381 posts, RR: 3
Reply 18, posted (7 years 3 months 3 weeks 4 days 15 hours ago) and read 5842 times:

Quoting Starlionblue (Reply 17):
The Gimli Glider incident would have been one case where Boeing could recommend all it wanted. The landing would have been attempted without any engines on.

If I recall correctly, until the Gimli Glider incident, Boeing had no procedures in the manual covering a dual flameout, and hence no best rate of glide speed in the 767 manual (the Gimli Glider flight crew were just guessing on that one...). It was because the engineers figured the possibilities of that happening were very remote...  scratchchin 



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 19, posted (7 years 3 months 3 weeks 4 days 15 hours ago) and read 5813 times:

I am sure the 744 has a battery, which should provide essential power for some period of time, in the event of a four engine failure.

User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 20, posted (7 years 3 months 3 weeks 4 days 14 hours ago) and read 5791 times:

Quoting 777WT (Reply 2):
Then if that's the case, then howcome 747's don't need RAT since 4 windmilling engines is more than enough to provide hyd power?

Chances of loosing all four are remote.Not saying it did not occur  Smile But then the Cause was different.
Then theres the APU & the Main Battery.
regds
MEL



Think of the brighter side!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 21, posted (7 years 3 months 3 weeks 4 days 13 hours ago) and read 5756 times:

Quoting 474218 (Reply 19):
I am sure the 744 has a battery, which should provide essential power for some period of time, in the event of a four engine failure.

It has several. But electrical power alone doesn't do that much good. What is needed is hydraulic pressure to control the flight surfaces. AFAIK the batteries cannot provide drive the hydraulic pumps.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSfomb67 From United States of America, joined Dec 2005, 417 posts, RR: 0
Reply 22, posted (7 years 3 months 3 weeks 4 days 13 hours ago) and read 5750 times:

[quote=HAWK21M,reply=20]Chances of loosing all four are remote.

I think there have been several 4 engine flameouts on 747's. Most attributed to fuel tank problems. I'm sure it's a busy flt deck when that happens, and I'm sure its not widely publicized.



Not as easy as originally perceived
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 23, posted (7 years 3 months 3 weeks 4 days 13 hours ago) and read 5749 times:

Quoting Starlionblue (Reply 21):
It has several. But electrical power alone doesn't do that much good. What is needed is hydraulic pressure to control the flight surfaces. AFAIK the batteries cannot provide drive the hydraulic pumps.

Windmilling engines will provide more than ample hydraulic pressure to the PRIMARY flight controls. The problem is when you have to slow down, the pumps are volumetric and can't power the flight controls and extend the flaps.

I will let all the "experts" on here take it from now on because they have so much more experience flying the 744, oh that was MSFS......


The APU on the 747 could be started in flight, but only after a mod was done. It was not part of the standard 747 delivery package. The 744 APU can not be started in flight. You should have ESS AC and DC for about 25 minutes.


User currently offlineDH106 From United Kingdom, joined Jun 2005, 626 posts, RR: 1
Reply 24, posted (7 years 3 months 3 weeks 4 days 10 hours ago) and read 5693 times:

Quoting Starlionblue (Reply 17):
The Gimli Glider incident would have been one case where Boeing could recommend all it wanted. The landing would have been attempted without any engines on.

Notwithstanding my earlier comment, I wasn't trying to be facecious here with this one.
Boeing has no contingency/recommendations for getting a 747 down with 4 engines out ?



...I watched c-beams glitter in the dark near the Tanhauser Gate....
25 PhilSquares : As I wrote earlier, they recommend against trying to "deadstick" a 747/744 due to the hydraulic problem and eventual reduction of windmilling RPM and
26 TristarSteve : Talking of hydraulic pumps on windmilling engines, let me digress a little. On the A320, we have a common problem of the aircraft flying with the yell
27 HAWK21M : I was aware of only one Incident.What are the others. Any reason. regds MEL
28 VC-10 : During internal leak troubleshooting on a JT9 powered 747 I got 3000 psi with 12% N2. Admittedly there was no flow, but the pressure was there.
29 PhilSquares : As I wrote, they're volumetric pumps... you'll get the pressure long before you get the volume. Just try actuating a flight control with 12%N1! Wasn'
30 DH106 : So, not to be too dramatic, but if you run out of fuel in a 747 - there's no real solution to your erm... problem? I do appreciate tho, that any deads
31 Steve332 : You could have all the company recommendations in the world, every page ever written on problems on any plane and have a gazillion hours in every air
32 DH106 : Yes, but my point is there appears to be no scenario to achieve this on a 747.
33 Jetlagged : AFAIK, all 747-200 APUs, as delivered, can be started in flight. I've never seen anything in the wiring schematics to show an APU variant which had g
34 Starlionblue : Well, I guess it's so unlikely that there is no such scenario. So many things would have to break to get to that point,
35 ArniePie : How long did it take before the KLM(over ALASKA IIRC) and BA (somewhere near INDONESIA) 747's need to restart their engines after they lost all 4 of t
36 Post contains images KELPkid : That's what I hate about statistics. There's lies, damn lies, and statistics. All it takes it one (albeit, rather unprofessional) aircrew to run a 74
37 VC-10 : Phil, I'm om your side! I was just trying to illustrate what low rpm was required to get full pressure
38 PhilSquares : Sorry, but that's just incorrect. Most were delivered so the APU could be used in flight, not started. In fact, all 747/744 are certified for infligh
39 ZANL188 : Sometimes you gotta take a step back and read what you post the way others read it. I have a technical background and have been working with heavy ai
40 Starlionblue : Well, true. However the Gimli Glider was caused by failure to follow ALREADY ESTABLISHED procedures. So was Air Transat 330. In the end, there is ris
41 PhilSquares : This is out of the FCTM. Multiple Engine Failure Multiple engine failure is a situation that demands prompt action regardless of altitude or airspeed
42 Jetlagged : I'm pretty sure of my facts. There is a difference between approval for start or use in flight, and being electrically inhibited from starting. The 7
43 Post contains images Jetlagged : As long as you don't pump the brakes and there is no leak in the return line the brakes will work, but at something less than 3000 psi of course. It'
44 Post contains images Qantas744ER : This really bugs me... Some "armchair pilots" here just dont seem to understand that people like Philsquares in this case talking about the 744 are ri
45 Bellerophon : Jetlagged ...BA didn't use to use the APU for no bleed takeoffs... Yes they did, on the B747-400, until recently. ...APU bleed for the packs? How many
46 Post contains images Jetlagged : Apologies, I should have stressed I was refering to the 747-200, though of course it's years since they operated those. I'm not saying they never use
47 PhilSquares : If BA used or not, I really don't care or dispute that. However, with a bleed off takeoff, you can still have the packs running via the APU bleed (al
48 G-CIVP : "it can seem like an eternity to those passengers sitting down the back of a hot aircraft". Tell me about it! It isn't too pleasant but bearable. I'm
49 Meerkat : Coincidentally there was a programme on NatGeo this morning about the BA009 four engine out incident. It was caused by volcanic ash from an erupting v
50 Post contains images Jetlagged : Last time I looked there were only three packs on a 744. Interestingly the engines didn't flame-out, but went into an irrecoverable sub idle stall. I
51 PhilSquares : Absolutely correct, my mistake....
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