Engine failure on a twin

[JetSetJ]

Hi there,

I was just wondering if you guys and gals could possible contribute to a discussion i've been having. If one of the engines fail on a twin engine aircraft, which would be the most preferable wind direction? The live or dead side and why?

My thoughts initially were from the dead side as the engine fails you get the obvious yaw. If the wind is coming from the dead side it would help to counteract the yawing tendency of the aircraft. However, will the aircraft not have the tendency to weathercock into wind thus increasing the tendency to yaw towards the dead engine??

Many Thanks,

JJ

[Wizofoz]

In what phase of flight? The only time wind direction will make any differece is during take0ff and (to a lesser extent) on landing.

For a failure during the takeoff roll, wind from thë "live" side will mean less rudder input required, thus less drag.

Once airboure, however, the wind does not effect the aerodynamic performance of the aircraft at all.

(Standing by for the whole "Down-wind turn" debate all over again!!!)

[747dieseldude]

The biggest effect would be on light-weight takeoffs, where v1 is vmcg limited, with engine failure around v1 and wind from the failed engine side.

I don't remember the certification standards exactly, but
i think it's 7 knots crosswind on a wet runway or so.
So anything above that, or a slippery runway could be a problem.

[Mad (Flt) Scientist]

i think it's 7 knots crosswind on a wet runway or so.

That's sort of the old CAA standard.

The current regulations and their interpretation requires no specific crosswind, and a pseudo-wet runway (NWS disabled, but you still test on dry, so the mains work as normal).

Which means that you're starting even further away from the crosswind case with the regulatory numbers ...

[B2N2]

In flight there is no difference. The airplane moves through a "block" of air, it doesn't care which way the block of air is moving.

I would only assume a difference on landing, a crosswind from the dead side would make de crabbing ( un crabbing?) more difficult.
If I have a choice of runways with equal crosswind I would chose the one with the crosswind on the live side, the tendency to weathervane will assist in aligning the aircraft with the centerline.
But what do I know.....

[Mäx Reverse]

The 'critical' Engine is the one on the upwind side, i.e. on the side which the wind is coming from.

Reason is that is wind is pushing against the horizontal fin and thus pushing the airplanes nose 'into' the wind. If the wind is coming from the port side and the No.1 Engine fails, the starbord engine is going to push the airplanes nose even more to the left, so this is the quickes way you encounter control problems.

Regards MAX

[downsouth]

Douring take off and landing, definitely its better wind from the live engine...

[IRRenewal]

The critical engine is the one still running, since it is absolutely critical that it continues to do so and drags you around the circuit in one piece.

Sorry, couldn't resist.

[Old Smokey]

If you consider a cross-wind in flight, we simply alter the Heading of the aircraft to compensate for the drift, and rudder input is not necessary. On the ground, however, we cannot allow drift, and must use rudder to off-set the yawing moment caused by the cross-wind in order to keep the aircraft tracking down the runway centre-line.
If there was. for example, a strong cross-wind from the left, the aircraft would tend to "weather cock" towards the left, and right rudder would be required to keep the aircraft straight. Some of the rudder authority to the right has already been used, leaving less rudder authority in that direction to compensate for an engine failure of the left engine/s (i.e. the up-wind engine/s). Thus, more rudder input will be needed for a failure of the up-wind engine/s, and conversely, less rudder input required for a failure of the down-wind engine/s.

All of this applies between Vef (just below V1) and the point where the aircraft leaves the ground, just after Vr.

Once airborne, drift is compensated for with Heading change, and fairly equal rudder input should be required for an engine failure on either side of the aircraft. (The fore-going is true for a jet aircraft, there may be assymetric propeller thrust considerations at high angles of attack for a propeller aircraft).

Regards,

Old Smokey

[bubbers44]

Remember, dead foot, dead engine. I think you got your rudder inputs for engine failure backwards.

[Old Smokey]

Thanks bubbers44, suitably corrected, foot dyslexia!

As chance would have it, I posted at the end of a long day of OEI training, thank goodness they didn't have my foot dyslexia, they seemed to do it OK, all 3 passed

Regards,

Old Smokey

[bubbers44]

OS, it took me a while to understand why toilets flush in a clockwise direction down under. Thanks for not keeping me up at night trying to figure this one out. Good night.

[john_tullamarine]

.. now that's a new angle .... I've never bothered to watch which way the loo flush charge rotates .... learn something new every day on PPRuNe ... is there any correlation with aircraft heading at all ?