Eng Failure in a Crosswind

[Hubble]

Starter for Ten!!

Would anyone be able to explain to me if its better to lose the upwind or downwind eng in crosswind take-off?

I've thought about this loads initially believing it to be better to lose the downwind due to the weathercock tendency.. That is if the upwind was lost,acknowledging the wxcock tendency, there would be more yawing moment for max rudder deflection...Alternatively, this wxcock tendency would therefore aid the pilot in regaining control if the downwind was lost!

However now i'm thinking.. Hmmm if i lost the critical no.1 (Turboprop) with a left hand crosswind (upwind) then i'd be better off cos i need less rudder input on the live no.2??? I am confusing myself..

Thanks in advance..

H :confused:

[expedite_climb]

This is how i see it.

Crosswind take off (both engines). You need rudder to head straight ahead. If you keep this rudder you will track to one side after take off. So you relax and use NO rudder.

Crosswind take off (engine fail). You still want to TRACK ahead. So you still want to weathercock to one side. You use the rudder to prevent it going left / right of the weathercocked hdg.

Therefore there is no preference which side fails, you will need no more / less rudder, as if you use the same amount as normal, the a/c will weather cock - what you want it to do.

Ok ?

:D

[Sink Rate]

Here are my thoughts and ramblings:

Engine failure before V1:
Better to lose the downwind engine as you will be stopping on the runway and the wind will blow any smoke away from the fuselage.

Engine failure after V1:
Better to lose the upwind engine as the aircraft will naturally tend to yaw towards the failed engine. In this case that is into wind which will offset slightly the track deviation. In my expereince in simulators crews often tend to not put enough rudder in initially thus leading to some drift downwind and thus head off track (SID / Emergency Turn). This effect is reduced if the upwind engine is failed.

[Hubble]

Thanx Guys!!

I think that clears things up a bit - i too would slightly favour having lost the upwind!!

H :)

[bakedbean]

I THINK IT WOULD BE BETTER TO LOSE THE UP WIND ENGINE.IN A/C SUCH AS F27 RUDDER AUTHORITY WOULD CERTAINLY NOT BE ABLE TO COUNTER A STRONG XWIND AND AN ENGINE FAILURE ,IN MY OPINION OF COURSE BUT WHAT A/C ARE YOU FLYING. :) :)

[bakedbean]

OOPS I MENT THE OTHER RIGHT....IT IS BETTER TO LOSE THE DOWN WIND ENGINE FOR THE REASONS MENTIONED IN IN MY PREVIOUSLY,EMBARASSING POST, IN MY OPINION.I WILL STOP BLUSHING SOON. :) :) :)

[P22]

Let's consider a take-off with a crosswind from the left. The wind will try to force the fin to the right, and therefore the pilot will apply right rudder to keep the aircraft straight. If the left (upwind0) engine fails at V1, then the pilot must apply even more right rudder to keep the aircraft straight until Vr. As the V1 must always be equal to, or above Vmcg, then this should be OK, but on aircraft such as the B747, Vmcg is calculated with a maximum crosswind of 7 knots (Vmcg has been covered on previous threads). Therfore between V1 and Vr an upwind failure is the most critical.
However, once airbourne, the limitations of Vmca become predominent. Immmediately after rotate, the pilot will still be applying right rudder and left aileron. Now, a failure of the right engine will require him to transition from right rudder to left rudder, at the same time keeping the wings level with the ailerons. A failure of the left engine will only require an increase in the already applied right redder, once again keeping the wings level with the ailerons.
So it can be seen that between V1 and Vr, the upwind engine is the most critical, and immediately after Vr, the downwind engine is the most critical. As Vmca is generally less than Vmcg, then the case between V1 and Vr is the most critical. Of course once the rotation is complete, and the 'crossed controls' are neutralised, it makes no diference which engine fails.

[mutt]

P22

Although this figure of 7 knots crosswind for VMCG calculations was mentioned in our last discussion on VMCG, I don’t remember anyone actually stating a document that could be used to justify this statement.

Do you happen to know a reference for this 7 knot requirement?

Thanks.

Mutt

[Bellerophon]

Elevation

I think you may need to re-read what P22 has written. Nowhere does it say that the rudder is blown to the right by the wind. P22 said, and meant, the fin. In a crosswind take off, on the vast majority of modern aircraft, the (outboard) upwind engine is the critical engine, for the reasons given.

P22

I also remember the B747-100/200 series being Vmcg certified only to a 7kt crosswind, with the correction to Vmcg being +1.33 kts per extra knot of crosswind. As was discussed in a previous thread, this could result in the actual Vmcg during a 27 kt crosswind take off being nearly 27 kts higher than the nominal Vmcg.

Once airborne, I think I would describe the downwind engine failure as requiring slightly more co-ordination (and therefore being slightly more difficult) rather than being critical, at least in the sense we use the word critical before Vr, meaning the ability to remain on the paved surface until either lift-off or coming to a halt.

From my observations in the B747 simulator over the years, any engine failure immediately after lift off was significantly more difficult, and rarely as well handled, as an engine failure immediately after V1.

mutt

The only reference I’ve got is my UK CAA Base Training notes for the B747, so I can’t provide the definitive source you seek, but from memory, that was the figure, and the correction, that was in use. I’d be the first to admit that this is not conclusive!

[quid]

I don't know anything about flying turboprops, but the following applies to jets.

We have a simple phrase for 3 engine ferry ops. "Good engine, good wind. Bad engine, bad wind". This means you want the wind coming from the good engine side. If you're taking off on 36, and have a crosswind from 090, you're going to use some of the rudder to keep it going straight. The more wind, the more rudder. Now, if the right engine fails, you may not have enough rudder throw left to keep it on the pavement.

Once it's in the air, it makes no difference.

Bellophon-

>>, any engine failure immediately after lift off was significantly more difficult, and rarely as well handled, as an engine failure immediately after V1.<< I see this all the time. Two reasons, I think. 1. The lack of visual clues. 2. Most pillots have had quite a bit of practice with V1 cuts, and are expecting them in the sim. Once airborne, the mind set is "OK, no V1 cut, so it will be a normal climb out". A V2 cut at 200 agl comes as a big surprise.

[Hubble]

Thanx guys - Loads of good info there...

I did have one other question for those of u who know the 747..( i wanted to know general EPRsettings for the classic for low level 2000'ish downwind, base and approach, starting at 280 kts... I'd better start another thread.. Thanx for the help again!

[mutt]

Bellerophon

Thanks for that, the 7 knot figure is one which I have heard for many years on CAA certified aircraft. But I don’t know if the rule still applies and I can’t find any reference to it in the JAR’s.

I’m 99% sure that there isn’t a requirement to account for winds when calculating VMCG for a FAA certified aircraft.

I know that we discussed this a couple of months ago, but with so many new people joining Pprune, I reckoned that it was worth asking again.

Cheers.

Mutt :)

[Captain Airclues]

The 747 certification did use a 7 knot crosswind to calculate Vmcg. The CAA and the FAA accept that the chances of an aircraft in line flying having an engine failure at exactly V1 are small enough for a higher croswind to be ignored. However, in the days when we used to carry out engine failures during base training, it was important for the training captain to be aware of this fact, as he knew that he was going to fail the engine at V1. He would therefore take the crosswind into account and incease the V1 accordingly. I know that a lot of people have strong views on this, so don't shoot me, I'm only the messenger.
I agree that a downwind failure just after rotate generally looks messy as the pilot transfers the rudder from one direction to the other.

Elevation

The 747 rudder has very powerful hydraulic controls, so I doubt that even the strongest crosswind would move it. The crosswind does however have a considerable effect on the fin, which is why rudder opposite to the crosswind (crosswind from the left = right rudder) is required.

Airclues

[ 16 November 2001: Message edited by: Captain Airclues ]

[john_tullamarine]

P22,

Vmcg is figured for nil wind (US) and 7kt (UK) - not sure what JAA opts for. This leads to the occasional silly difference between the RTOW data for one operator compared to another where the minV1 in the UK AFM is higher than the corresponding US AFM.

On what basis do you state that Vmca generally is less than Vmcg ?


Mutt,

The US document is AC 25-7A at whatever issue is current - I am relying on memory for the number as I am away at the moment. My file copy is superseded and I have yet to get around to updating it - the AC at the issue I have requires that Vmcg be predicated on nil wind and I would be surprised if that has changed.

I have seen the 7 kt reference in a number of BCAR AFMs and, as I recall, we did chase up a source document about 20 years ago when we were playing with a lovely old queen of British technological prowess armed with lots of wind-walloping engines - actually we were playing with a number of them. I don't suspect that the document is still on our files and can't for the life of me remember the detail. Suggest you direct the question to Genghis - he should be able to help without too much effort - after all, he is in the right sort of place to dig it out of the archives.

Bellerophon offers a 747 Vmcg correction figure of 1.3kt/kt crosswind - quite alarming - I had always worked on a rough figure of 0.5kt/kt (for twins) based on manufacturer's data provided for a specific flight test program.

Either way, if a takeoff be predicated on minV1, the altitude/OAT be thrusty, and the cg be aft, then a strong crosswind could well see the pilot losing control above V1 in the event of an engine failure on the windward side - as the wind provides an additive destabilising yawing moment not considered in the certification process.

As to whether this situation is likely to occur or not is not the point at all. The pilot ought to be aware of the problem so that a suitable operational decision appropriate to the day can be made as and when the situation calls. Captain Airclues makes some very relevant observations regarding base training.

Contemplating where pilot handling is most demanding for a failure, I suggest not at V1 or 200ft, but rather during the rotation flare just as the pilot loses the visual horizon reference. At this point the manipulative workload and I/F scan requirement is most demanding and the potential flight path gyrations the most interesting - especially if bank is ill-controlled with a subsequent Vmca departure. I train progressively to competence at conditions of minV2/min AUW, aft CG, SL STD conditions with a bird strike if the sim has that option. When the guys can handle that comfortably, their confidence is maximised and anything else is no sweat. One also must train at the high weight, high altitude, high deviation end of the spectrum to cover the situation which is most demanding from the viewpoint of milking every drop of performance from the aircraft following a failure.

And we all take great pains not to go outside the obstacle splays ..... don't we ?

[ 16 November 2001: Message edited by: john_tullamarine ]

[P22]

john

"On what basis do you stae that generally Vmca is less than Vmcg?"

The Boeing chart 'Air Minimum Control Speeds (One Engine Inoperative) in my 747-400 manual shows Vmca for 15 degrees C and a Pressure altitude of 0ft as 117 knots. The table for Vmcg for the same conditions shows 126 knots. Of course the FAA Vmcg figures may be lower.

[john_tullamarine]

P22,

Thanks for the clarification. I read your earlier post to suggest that your observation was general, not specific to one machine.

If your bird is UK certificated then I would expect that the equivalent US manual would show a lesser Vmcg.

[Hugh_Jones]

My understanding of the 7kts crosswind is that it was included in the CAA certification process, however with the advent of JARs the 7kts crosswind no longer applies. This brings JARs in to line with FARs. Therefore all aircraft pre JARs ( I believe the A320 was the first JAR certification) will have been tested using 7kts and post JARs 7kts is not used.

[Elevation]

P22 and Bellelophon,
I indeed read it wrongly.
Post withdrawn.
Thanks for pointing it out.

[2daddies]

The Cathay Pacifc style answer to this question (derived from D.P Davies' Bible, "Handling the Big Jets") is that the critical engine at or below Vr is the most outboard upwind engine because of the combined effect of assymetric thrust and weathervaning making control of the aircraft on the runway difficult.

After Vr (once airborne) the critical engine is the most outboard DOWNwind engine because of the combined effects of assymetric thrust and crosswind-induced drift making extended centreline tracking difficult.

Obstacle Clearance after take off is ensured by a surveyed, splayed area commencing at the departure end of the runway which has nothing in it which can be hit. Not tracking the centreline accurately after a critical (or any kind!) of engine failure could take you outside of this splay, where there is NO obstacle clearance guaranteed.