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ZBBYLW
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Quad Double Engine Failure Question

Thu May 14, 2009 2:42 pm

Having never flown a Quad, and just Twins at best I have a question that I have never seen answered before.

If say a Quad is taking off and is now past V1. At this point say the aircraft has a multi bird strike, and lets also say that the aircraft is light enough that it could fly on 2 engines. All 4 engines are producing take off thrust and they loose both 1 & 2 or 3 & 4. The aysymetric thrust I could imagine would be unreal (especially with 1 or 4 being so far out on the arm). Providing the aircraft is light enough that 2 engines can sustain flight (and even climb) would the aircraft theoretically be able to have enough power on to climb away, or would the 2 engines (at full power) basically be too much and the flight end rather spectacularly.

Just a question that really would be a very rare occurance (though we see what happened to US). I personally think (total guess) that the a/c would not be able to fly with 2 failures on the same side, providing it needed to climb. I know that if at cruise they could regulate their descent with power and make it down.

What say you?

Edit to add: Is there a published Vmc for double engine failure on one side? If so what would it be? I would imagine it would be VERY high. Also is there a Vmcg for this senario where say this happens somewhere between V1 and Vr at TOGO thrust?

[Edited 2009-05-14 08:16:38]
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Jetlagged
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 3:25 pm

A 747 can climb on two engines and can go-around on two as well, so assuming the aircraft made it into the air then it could continue to climb and make it round for an emergency landing. Close to V1 the asymmetric thrust could well be uncontrollable without a reduction in thrust on the operating engine side, which might then make lift off impossible.
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ZBBYLW
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 4:12 pm



Quoting Jetlagged (Reply 1):
Close to V1 the asymmetric thrust could well be uncontrollable without a reduction in thrust on the operating engine side, which might then make lift off impossible.

Thats what I am thinking, at 300 kts the rudder will have enough authority. What percentage of the MTOW roughly (standard day) can the 744 do a go-around on two engines?
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Jetlagged
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 5:06 pm



Quoting ZBBYLW (Reply 2):
Thats what I am thinking, at 300 kts the rudder will have enough authority. What percentage of the MTOW roughly (standard day) can the 744 do a go-around on two engines?

I suspect you'd be able to climb and maintain heading at much lower speeds than 300kts. You'd need to be talking to a pilot about specifics, but a go-around would not normally happen above maximum landing weight. MTOW is 800,000lb and MLW is 652,000 lb, so I'd guess a two engine go-around could be performed at 81.5% MTOW, possibly more.

PhilSquares would be able to give you the low down on 744 performance in this case.
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SEPilot
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 5:27 pm

Interestingly, the only two airliners that have had fatal crashes due to bird strikes were in fact both quads. One, however, did not lose the engines, it lost the horizontal stabilizer. As to the question at hand, I do not believe that a fully loaded 747 can climb on two engines, although it probably could maintain altitude. If the load is light enough than there are a lot more possibilities. I will certainly defer to 747 drivers on this, though.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
2H4
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 5:37 pm



Quoting SEPilot (Reply 4):
I do not believe that a fully loaded 747 can climb on two engines, although it probably could maintain altitude.

Yet another application for 2H4's patent-pending BaggageDump® system!

2H4
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flipdewaf
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 5:49 pm



Quoting 2H4 (Reply 5):
Yet another application for 2H4's patent-pending BaggageDump® system!

Does that make all the women fall out?  duck 

Quoting SEPilot (Reply 4):
although it probably could maintain altitude

Surely if it could maintain altitude x it would be able to climb to that altitude?

Fred
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SEPilot
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 5:58 pm



Quoting Flipdewaf (Reply 6):
Surely if it could maintain altitude x it would be able to climb to that altitude?

Not at all; maintaining a certain altitude requires a certain amount of thrust; climbing to that altitude requires a significant excess over that thrust. The UA 747 that lost its baggage door near Hawaii actually lost 3 engines due to debris ingestion; it was not quite able to hold altitude on the remaining engine but was able to keep the descent rate low enough that it was able to land safely before it ran out of altitude. It certainly would have been incapable of climbing at any point.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
flipdewaf
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 6:10 pm



Quoting SEPilot (Reply 7):

But isnt all thats required for climb excess thrust? At the lower altitude you will have this excess thrust.

Fred
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DocLightning
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 8:19 pm

Well here's my question.

As I understand it (and the only plane I've ever flown was a paper airplane I made in 2nd grade), V1 is calculated based on the assumption that you will lose one at that speed.

So if you lose two (let's assume, for simplicity that it's a symmetrical loss on 1 and 4...two unlucky pelicans), you could eventually take off (F=MA) given enough runway, but since runways aren't ten miles long, my guess is that you'd wind up in the drink at the end of the runway before you actually rotated.

In other words, a dual engine failure on a quad at V1 is probably going to have the same end outcome as a dual engine failure on a twin. However, on a quad, it might be even worse because the remaining engines would be thrusting when you smashed into the ground.

What do you more knowledgeable folks think?
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Jetlagged
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 8:38 pm



Quoting DocLightning (Reply 9):
In other words, a dual engine failure on a quad at V1 is probably going to have the same end outcome as a dual engine failure on a twin. However, on a quad, it might be even worse because the remaining engines would be thrusting when you smashed into the ground.

Not necessarily, you have the option of putting the remaining engines to idle and trying to stop.
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SEPilot
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 8:42 pm



Quoting Flipdewaf (Reply 8):

But isnt all thats required for climb excess thrust? At the lower altitude you will have this excess thrust.

Not really; as you gain altitude thrust decreases, but so does the thrust requirement, as the reason thrust decreases is that the air is thinner, but that also reduces drag. So the amount of excess thrust changes little. It is true that thrust decreases faster than drag, which is why aircraft have ceilings based on available power. But I suspect that the effect is not enough to let a fully loaded 747 climb on two engines.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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Jetlagged
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 9:01 pm



Quoting SEPilot (Reply 11):
But I suspect that the effect is not enough to let a fully loaded 747 climb on two engines.

From high altitude a 747 on two engines would drift down to a particular flight level. Below this level it should be able to climb, maybe not quite to the same level but nearly so. Any amount of excess thrust will allow an aircraft to climb, however slowly.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
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SEPilot
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RE: Quad Double Engine Failure Question

Thu May 14, 2009 9:09 pm



Quoting Jetlagged (Reply 12):
From high altitude a 747 on two engines would drift down to a particular flight level. Below this level it should be able to climb, maybe not quite to the same level but nearly so. Any amount of excess thrust will allow an aircraft to climb, however slowly.

Theoretically you are probably correct; however, I suspect in practice that the climb rate would be so slow as to be impractical.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
411A
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RE: Quad Double Engine Failure Question

Fri May 15, 2009 4:20 pm

JED, circa, 1984.
B747SP
Intended route, JED-JFK
Rny 34L
Temp 26C
Wind calm.Acft at MTOW

At 400 agl, very high vibs were noted from number two engine.
Throttle retarded, vibs decreased significantly.
Throttle again advanced.
Number two engine went BANG, all thrust from same ceased, and in addition, bits from number two entered the intake of number one, causing a fire pull handle light to illuminate on number one, but no fire bell.
Meanwhile, the Flight Engineer, noticing that the fire pull handle for number one engine was illuminated, and not noticing that number two engine was now not producing any useable thrust, promptly pulled the fire pull handle for number one engine...without saying anything to any body.
Result?
The airplane was now at 900 msl, at max weight, on two engines.
The Captain (a good friend of mine) started a very slight descent for accelleration, asked the First Officer to retract the flaps on speed schedule, asked the now dumbfounded Flight Engineer to start immediate fuel dumping, and....at 200 msl, over the beach, managed to arrest the descent and start a very shallow climb.
The aircraft was climbed to 1000 msl, turned downwind, and landed again on 34L.

I personally watched it all happen from my TriStar, whilst waiting for takeoff clearance behind the departing SP.

The Flight Engineer was terminated the very next day, and received an exit visa, poste haste.
He was very lucky to have not been thrown promptly in jail.
 
nomadd22
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RE: Quad Double Engine Failure Question

Fri May 15, 2009 4:29 pm

I flew for close to 500 miles on a C-130 with both port engines out in 83. It was very lightly loaded, but the pilot said it was remarkably unpleasant to fly.
Anon
 
2H4
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RE: Quad Double Engine Failure Question

Fri May 15, 2009 4:47 pm



Quoting 411A (Reply 14):
causing a fire pull handle light to illuminate on number one, but no fire bell.

If the fire bell indicates the presence of flames, what does an illuminated (and silent) fire pull handle indicate?

2H4
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411A
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RE: Quad Double Engine Failure Question

Fri May 15, 2009 5:53 pm



Quoting 2H4 (Reply 16):
If the fire bell indicates the presence of flames, what does an illuminated (and silent) fire pull handle indicate?

On some types, one loop only senses an overheat condition, the other does not.
Dunno on the 747, don't fly these.
 
vikkyvik
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RE: Quad Double Engine Failure Question

Fri May 15, 2009 6:45 pm



Quoting SEPilot (Reply 11):
Not really; as you gain altitude thrust decreases, but so does the thrust requirement, as the reason thrust decreases is that the air is thinner, but that also reduces drag. So the amount of excess thrust changes little. It is true that thrust decreases faster than drag, which is why aircraft have ceilings based on available power. But I suspect that the effect is not enough to let a fully loaded 747 climb on two engines.

An airplane's theoretical max altitude is based on excess thrust. You'll hit your max altitude when you have just enough thrust to maintain level cruise, but no excess with which to climb.

At any altitude below that, you have excess thrust (however little it may be), and can climb.
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Fly2HMO
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RE: Quad Double Engine Failure Question

Sat May 16, 2009 1:48 am

Back tracking a bit... so lets say a 747 at MTOW lost engines 3 and 4 right at V1. Will the plane yaw uncontrollably to the right (picture a VMC roll/yaw)? Or is the rudder able to overcome that at those slow speeds?
 
CosmicCruiser
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RE: Quad Double Engine Failure Question

Sat May 16, 2009 2:36 am



Quoting 411a (Reply 17):
On some types, one loop only senses an overheat condition, the other does not.

What does it indicate then? At least on the jets I've flown they both are redundant therefore one can be deferred inop and still have fire protection.
 
ex52tech
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RE: Quad Double Engine Failure Question

Sat May 16, 2009 3:42 am



Quoting 411A (Reply 14):
JED, circa, 1984.
B747SP
Intended route, JED-JFK
Rny 34L
Temp 26C
Wind calm.Acft at MTOW

Saw a similar situation as that happen at an airline that I worked at. 742 with JT9-7Qs.

#2 had an un-contained turbine failure right as they rotated ( we heard and saw it) the #1 in-jested engine parts, and started compressor stalling. At first we thought the #1 had let go, and I was wondering why they let it continue to stall, or run for that matter, as they were coming back around into the pattern, not knowing they had shut #2 down already.
My crew was sent out to tow that one into the hangar after all the hub-ub died down. The #2 aft cowls looked like someone had hit them with a machine gun. What really caught my attention was several gouges in the bottom of the wing, one that was almost through the lower skin. Makes one wonder what might have happened if that turbine blade had entered that fuel tank.

The #1 was a mess, some gouged and torn fan blades, metal in the tail pipe. The JT9 has to be the toughest high bypass engine I ever worked on or ran. I don't know all the particulars about that flight, such as how heavy they were, or how bad the airplane was performing on 2 good engines, and one that was in the process of coming apart, but I can count on one hand how many un-contained engine failures I have seen in 25 years of working on airplanes. Out of that small number two were un-contained turbine failures.
"Saddest thing I ever witnessed....an airplane being scrapped"
 
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Jetlagged
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RE: Quad Double Engine Failure Question

Sat May 16, 2009 11:20 am



Quoting 411a (Reply 17):
On some types, one loop only senses an overheat condition, the other does not.
Dunno on the 747, don't fly these.



Quoting CosmicCruiser (Reply 20):
What does it indicate then? At least on the jets I've flown they both are redundant therefore one can be deferred inop and still have fire protection.

The 747 Classic and 747SP have two basic fire system types (Graviner and Kidde) that can be installed and wiring options on each (basically AND or OR logic). Each loop can indicate a fire condition (overheat) or a fault condition. It's up to the F/E to interpret the indications. Some wiring options require both loops to indicate fire, some will indicate fire if both loops show fault, and all variations in between. In addition the F/E can isolate a faulty loop, leaving the single remaining loop to detect fire.

So it's entirely possible the 747SP in question could have a fire light but no bell, and the F/E in question ought to have known what that meant on his fleet.
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glen
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RE: Quad Double Engine Failure Question

Mon May 18, 2009 2:34 pm



Quoting ZBBYLW (Thread starter):

To get back to the start of this topic:

The A343 for example has a service ceiling of 4200 ft at MTOW at Temperatures ISA+10 and below with 2-eng inop. But this is calculated in clean configuration. I doubt you will be able to continue with a second engine failure right after lift-off, because even a 2-eng out go-around isn't possible below 500 ft AGL. For a go-around above you have to trade some altitude to retract flaps and gear.
The only chance after take-off is if you are lightweight and have no obstacles.
So there is no Vmc published for 2-eng out at departure. However there is one for the approach (app. configuration, max. 5° bank, 2-eng out at same side, others at take-off thrust). It's 157 kts, which means it is considerably higher than the normal approach speed (142 kts at MLW).
You will keep this speed until you are below the commit altitude of 500 ft (see above), then reduce to your normal approach speed.
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PhilSquares
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RE: Quad Double Engine Failure Question

Mon May 18, 2009 3:21 pm



Quoting ZBBYLW (Thread starter):
Just a question that really would be a very rare occurance (though we see what happened to US). I personally think (total guess) that the a/c would not be able to fly with 2 failures on the same side, providing it needed to climb. I know that if at cruise they could regulate their descent with power and make it down

On the 744, the two engine max altitude at ISA+10 and below at 400 tonnes is 3900' pressure alt. However, there is a note that indicates, the published max altitude is actually adjusted 2000' for improved safety margins.

If you were to get on the dump right away with 2 engines out on one side, you would dump at around 2.5 tonnes/minute. At that weight you'd have most tanks full so the dump rate would be at the max.

For every 10 tonnes of weight reduction the ceiling climbs by about 1500'. So, you would have no problem getting the aircraft cleaned up and climbing out. The only real issue would be an engine failure that caused a reverser deployment on the outboard engine at MTOW.

The 2 engine QRH procedure prohibits a go around from below 500'. However, the aircraft will do it from around 200'AGL with no problems at all.
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ZBBYLW
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RE: Quad Double Engine Failure Question

Mon May 18, 2009 4:29 pm



Quoting GLEN (Reply 23):



Quoting PhilSquares (Reply 24):

Thanks you two, exactly what I was looking for!
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point8six
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RE: Quad Double Engine Failure Question

Tue May 19, 2009 8:51 am

An exercise that I used to run in the B744 simulator (time permitting at the end of the detail), was a take-off from SIN rwy 20L (now 20C) at +28 deg C and 380 tonnes T/O wt, with an outboard run-down at V1 and the adjacent engine failed at 800ft RA. It required a carefully flown gentle descent to accelerate and by retracting the flaps approx. 5 knots below bugged speed, it was possible to clean-up and climb away, throttling the operating outboard engine back slightly (for better directional control and wear-n-tear on the knee!). Until 280 knots was achieved, it was impossible to turn against the live engines (outboard aileron locks out when flaps are retracted and inboard aileron is quite small), however, at or above 280kts full manoeuvrability is available. Immediate fuel-dumping (at 2.5 tonnes per minute) is perhaps not worth the distraction from accurate flying. Dumping to max. landing weight is required for the approach and landing, especially for the go-around possibility. As Phil Squares states, a go-around is achievable from 200ft - though it is not a Boeing recommended procedure, and some airlines do not practise go-arounds once the gear is locked down.
As for climbing away safely, following the loss of both adjacent engines at or above V1 - I think that this would be highly unlikely, but not impossible. Vmca2 is approx. 162kts for the 744 (if my memory is correct).

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