747 Engine Failure

[husqvarna]

I did a search for the answer on this site, and didn't find anything the really fit, so excuse me if this topic is old.
I was wondering how many engines are required for a takeoff in a 747. I believe that twin engined planes are certified to take off on only one engine. I highly doubt that this is the case for the 747. Can it lose 2 engines and still become airborne? Furthermore, how many are required for continued flight once airborne and cruising?
Just curious.

[747FOCAL]

The 747 can fly with one engine if already at altitude. Depending on how heavy you are, how hot it is and the altitude of the runway you can lose two engines and still make it if your really lucky. Lose 3 engines and you probably didn't want to make the trip in that aircraft anyway :ok:

[Notso Fantastic]

We have recently been practising in the simulator heavyweight takeoffs losing one engine, then the other during the clean up. You have to jettison fuel to landing weight or below, but you can still continue climbing, albeit slowly. 2-engine out approaches are no problem at landing weight or below, nor go-arounds on 2.
To lose 2 at heavyweight/slowspeed before you have started cleaning up is probably pushing your luck too far- I don't think you could accelerate to start retracting flap without losing height, which you haven't got.

[PaperTiger]

To lose 2 at heavyweight/slowspeed before you have started cleaning up is probably pushing your luck too far- I have a faint memory of a CO 747 doing just that ex-LGW followed by a hairy circuit and landback. Google didn't find anything, anyone else remember this or am I completely senile ? 1980s ?

[gas path]

I believe that twin engined planes are certified to take off on only one engine.
Don't think I'd fancy being on one of them! However after decision speed you ain't got much choice:ooh:
Three engined take offs, on the 747 at least, are certainly not a problem, we use ferry flights to get back to base following an engine failure down route.
Basically start the TO roll on the two symetrical engines and slowly feed the other remaining donkey in at around 80knts (from what I remember???).

[Notso Fantastic]

Tiger, I think that was the one in a strong southerly wind lost the critical (#1) engine. It just made it over Russ Hill apparently with 30' to spare. Confused stories at the time that didn't seem to add up. Scared a lot of people, not least the farm animals underneath. Can't recall more.

[JW411]

Paper Tiger:

I might be able to help you a bit with the CO 747 that nearly hit Russ Hill on take-off from LGW. He lost an engine at V1 and climbed straight ahead. Many of us at the time wondered why he didn't do an emergency turn 25° to the left and so avoid the obstacle.

Later on in my career I discovered the answer. I had been flying DC-10s out of Gatwick for Laker and that was our procedure. Later in life I found myself flying the self-same ex-Laker DC-10s which were now on the N register. The identical aircraft could not come out of LGW at anything like the weights that we were used to.

The reason was that the FAA would not allow an emergency turn during the net flight path whereas the CAA would. Therefore the MTOW was predicated on avoiding Russ Hill in a straight line.

As you are no doubt aware we have to be able to avoid all obstacles within the net flight path by 35 ft in a straight line (and 50 ft in a turn) so therefore by missing Russ Hill by "about 30 ft" means that his take-off calculations were pretty accurate.

Having said that, I'm sure that I wasn't the only person at the time who wondered why the daft bu**er didn't look out the window, turn 25° left and so avoid all the grief! As best as I can recall the weather was pretty good that day.

[Intruder]

As all transport category airplanes certified in the US, the 747 can take off after an engine failure above V1. There is no certification requirement for takeoff with multiple engine failures.

That said, I have done so in the simulator, when the instructor failed to clear a #4 failure at V1 after adding in a #1 failure at V1. I got the [simulated] airplane off the runway, got the gear up, and was sslloowwllyy accelerating when the instructor reset the machine.

I suspect that in the real airplane it would be possible to take off on 2 symmetrical engines under ideal conditions (light weight, low temperature, long runway, second failure somewhat after V1, no obstructions). Note that we already use derated thrust at 80% max thrust for normal takeoffs at reasonably heavy weights.

We already practice (in the simulator) landings with 2 engines failed on the same wing. Single-engine landings are not practiced in general.

[PaperTiger]

Thanks all, I had it in my mind that CO had had a double failure (or maybe it was one failure and low EPR due fuselage blanking).

They say the memory's the second thing to go. Buqqered if I can remember the first :zzz:

[lomapaseo]

PaperTiger

You are partly correct. But in the end the analysis indicated that the pilot failed to correct the pitch attitude to account for the loss of performance.

Certainly not the first nor the last of the same lesson learned.

[BlueEagle]

And all this time I thought the one at LGW/Russ Hill was People's Express!:O

[PaperTiger]

Shortly after the takeover I think, Blue. Was probably still in the fawn paint scheme.