flyingchicken

Might as well add my 2c...

Agree, but this is a landing scenario. Minimizing drag is not a high priority.


VMCA is based on TOGA thrust. I seriously doubt you would be anywhere near that for the technique being discussed.

The effect should be much less than what you would experience on rotation from a V1 cut with the same crosswind, and we know the airplane can handle that.

Landing. Drag reduction not priority.

No worse than kicking out crab with rudder

This I can agree with. Its a case of risk management - whats your biggest threat for that approach, is it the crosswind, or is it engine failure in the flare?

Agree that this is not an approved procedure, and that the autoland does not use it. However in my current aircraft (A330) the autoland crosswind limit is only half of the demonstrated 40kts.

flyingchicken

Are you sure your AC specifically includes information on asymmetrical reverse?
I think the difference here is that your AC is talking about symmetrical reverse on both sides, where as I'm talking about asymmetrical reverse.

I believe the yawing moment generated and rudder sideforce required to counter the resultant yaw in the asymmetrical case should be much greater than the downwind component of any thrust line offset from reasonable crab angles.

Now if you have symmetrical reverse, then there is no resulting yawing moment and the downwind reverse component then becomes the primary factor, in which case I agree.

EDIT: Just realize the disconnect here... you were talking about MadDogs... MD80s perhaps? in that case you are right! Its because your engines are so close to centerline that the resultant yaw will be very minor when compared to equipment with wing engines.

jungle

That is a rather presumtuous statement lacking any data or recommendation from any major manufacturer. If you are prepared to pay the price for not really knowing the answer, have at it, and leave me behind.

shdw

Sweet I can address KC10 and you at the same time, love this. Of course you would because with an engine out as KC10 pointed out you are aiming for zero sideslip which means you will naturally lower the wing into the wind in this scenario. You likely wouldn't want to fly into a crosswind with the windward wing high. You wouldn't fly a sideslip OEI into landing either, or so I hope.

However, KC10, when you use asymmetrical thrust you are not giving it the same difference as is experienced in an OEI situation and you have control to change it at any moment. That is why I said you can use it to successfully eliminate approximately 10-15 knots of crosswind. If you have only a few percent difference in the engines, 5 maybe 10 percent, then the resultant sideslip using rudder is not appreciable but will allow you to use less crab without dropping a wing. There is nothing wrong, on the other hand, with flying in a sideslip during OEI, like you said though there are consequences but if you account for them it is still safe. Disclaimer: I am not saying to fly in a sideslip, only that even in OEI it is possible to do safely.



Jungle, it only annoys me because I already answered each question you asked not to mention the mockery. It was Seminole that I performed this in and I used a 200-300 RPM difference if I remember right (was 4 years ago). I also have not seen it in any manual, I was first told about it by a gentlemen who flew B-17 bombers in WWII at a local aviation show.



I am also not saying you should all go out and change your ways and use this every-time you land. However, to assume it is unsafe, especially when there are obvious conceptual errors, is a narrow minded approach to take to any situation. It does work, it has been used by other pilots as you have seen here, and it is not unsafe in anyway. With that I ask, why not have it in the toolbox as you all seem to like to say?

shdw

I suspect that is because of the KISS rule of thumb. They figure if they give pilots the go ahead to start playing with thrust some moron is going to screw it up and wind up making a big hole. Especially if they are applying this on short final, that is why I said to stabilize it early that way if you don't like it you can go around safely. The aerodynamics support it as that flash video I linked clearly shows, or so I thought.

shdw

I am unsure about the phrasing, "pulled," but the net effect will be a turn to the left.

He is right and here is how you can see it. Imagine your in a boat rowing along, you drop the left ore into the water (your reverse thrust), the boat turns left. Similarly if you have a left to right crosswind, the upwind side being the left side, if you drop the reverse thrust on the left engine (putting the ore in the water) the aircraft will turn left, or upwind, assuming it has forward motion when this happens.

Edit: Reverse thrust is nothing more than massively increasing drag on whichever side it is applied, usually both equally, just like dropping an ore in the water massively increases drag on that side of the boat.

Make sense?

Sorry for the triple posts by the way, just saw this.

KC10 FATboy

I have a few issues with what you typed to my response. The things I listed weren't just my opinion, but also from a flight manual book from the FAA.

Drag isn't a big issue if you have autofeather (preferred) or the ability to feather/windmill an engine in case you lose one. Which leads me to discuss VMCA. The fear here is that a pilot uses this technique poorly, goes around, applies power asymmetrically to the engines (downwind engine spooling up to go-around thrust first) while you were banked slightly into the upwind engine to kill the drift from the crosswind. This is EXACTLY when VMCA is going to kill you. Read this article. AvioConsult - Accidents after engine failure

When you have a V1 cut, after getting airborne, you bank into the good engine with 1/2 ball into the good engine --- or at least you should. But when performing this "technique", you are violating this principle.

As I said before, drag isn't that big of deal. The stall issue applies here too. This manuever doesn't seem to be one that you're performing in the flare. It sounds to me that you have to set it up first for it to work correctly. Shdw admitted that he did it from 2 miles. Not faulting him. But I wouldn't be applying forward-slip controls that far out either. So, drag, not that big of deal. Stall, yes. If I crab to a forward-slip, I'm doing it at the runway. And all I have to do is let go of the controls and I neutralize everything instantly. In this scenario, I have the get the power symmetric or pull the downwind engine -- neither of which is going to be as quick as the flight controls.

Look, we aren't going to agree. And that is ok. It's what makes the world go around.

But you are correct. It is all about risk management. What is more dangerous? Using this technique to give you extra crosswind capability or crashing because you had your aircraft in an odd flight manner when an engine failed?

Both are stupid because you should have never tried to land on a runway without having the crosswind limits in the first place. Which was my original point about 4-5 pages ago ... and is what other's were saying you could use this technique for. If you can't land using a traditional crab to a foward-slip, then don't land. Otherwise, you are needlessly addiding risk.

KC10 FATboy

Yes, it makes 100% sense. Just because the aircraft is pointed into the wind, doesn't mean it is tracking upwind. Nose wheels have been known to slide. Wind body forces (pushing you downwind), the reverse thrust (pulling you downwind) ... and if you are pointed into the wind, reverse thrust is pulling you off the runway. But don't believe me, take it from McDonnel Douglas. Why would they put a warning into the flight manual then? This is especially dangerous on wet or icy runways. That is why Boeing, McD, and I would suspect, Scarebus, all say to discontinue revers thrust if directional control cannot be maintained.

It doesn't matter if you are single engine or which direction the wind is from. You can use reverse thrust or beta (not restricted in any aircraft I've flown). However, if you get yourself turned into the wind, which could have happened from asymmetrical reverse thrust, the opposite of what you expected (going off the runway on the downwind side while pointing into the wind) may very well happen.

KC10 FATboy

The original OP asked whether this technique was valid for big and small aircraft.

Some intially said yes, but many seemed to be very against (concensus NO). Some argued that you pull the upwind engine, others said the opposite (mass confusion). Others said they've done it in big jets, even those that have a different procedure listed by the manufacturer. Of the people who admitted that they've done it, they said they used it during extreme crosswind cases.

One smart individual said that this technique really isn't required because most airplanes can be landed using traditional crosswind controls. And if you can't, just land somewhere else.

As Jungle said, this is something you'll have to sort out with your Captain on approach, or perhaps the FAA if it gets ugly.

KC10 FATboy

I believe in my previous post I showed how this technique can be dangerous. Whether you agree with me is another thing.

And as I've said all along, if I can't land an airplane using a traditional and accepted procedure, then it isn't a runway that I should be landing on.