Reverse Thrust & X/Winds
 

On a number of threads I have read that on landing with a significant crosswind, some pilots use asymmetric reverse thrust (if I have understood correctly) to prevent runway excursions.

Not having flown a jet I would like to understand what how exactly this is done. I presume reverse thrust is selected on the downwind side engine to offset weathercocking but I stand to be corrected.

Not really...
 

No, this is utter and complete XXXXXXXX. What XXXXXXX told you
this? So, as I always say....please show me in an authoritative
document where it says to do this.

As a young, inexperienced pilot, you will fly with many captains
who are so screwed up, you'd think they have mental problems.
Some of the XXXXXXXX they come up with is quite entertaining.
If the civil aviation authorities have a sense of humor, they'll
laugh like hell, just before they begin filling out the paperwork
for certificate action and issuing the fines....

The use of asymmetric reverse thrust is not a way to control an aircraft in any condition.

I have never heard of it being done, and it is specifically warned against in the Boeing manuals.

There IS a technique of cancelling reverse in the event of a skid, as the reverse will be "pulling you off the side of the runway" when the tail is pointing at the side of that runway, rather than in-line with the runway centre-line.

Chill out Pantload, the guy was only asking a simple question. Mis-informed as he may have been, there is no need to jump on your high horse and start a rant. Perhaps you're the one who should be taking the Prozac.

Gentlemen, I did say I might have misunderstood what had been said which is why I asked the question.

Is there a situation where reverse thrust may not be used because of a crosswind situation? That is, use of reverse thrust may cause the aircraft to become unstable during the roll-out.

To answer the last one, yes.

On some types the reverser plume interferes with the aerodynamics, either of the wing or the tail (depending on engine location). If the aircraft has limiting or marginal xwind capability, this plume interference may adversely affect the handling, further restricting the capability.

On Challenger 604, for example, the crosswind capability without using TRs is 24 knots DEMONSTRATED and no explicit Limitation exists. With use of TRs that 24 knots becomes a LIMITATION.

On other aircraft, limits are specified on the level of reverse thrust which may be used, in part to ensure adequate controllability is maintained. Loss of directional stability in a crosswind would be unpleasant. (Note - I doubt there is no stability at 24.5 knots - but the OEM and the cert authorities doesn't want you to go trying it to find out!)

I hate to start a fight here, but I guess I'm going to anyway.

I have used asymmetric reverse thrust in jet aircraft in strong cross winds on contaminated runways and had zero problems.

Yeh but are you talking Deisel-8s or 707s Con? And 727s
and DC9s have thrust vectors close together, so the assy
effect would be diddlys.

A slight assymetric reverse on the 737 helped a bit in the
rare contaminated landings I've done (snowy ice slop) but
I'd never try it in a Scarebus - too many things could go
wrong on the bloody thing.

I love this statement and it is not a kick in the shorts to scarebus. The whole bloody industry has changed SO much over the past several decades. Airlines do not want pilots, they want operators who follow policy and procedure. Airbus jumped on this cultural change quickly and killed a 320 at an air show years ago as a result..(screwed up again just a few days past).

Suppose the question is who or what the hell is flying the aircraft? Why have a pilot when automation possibilities are advanced enough to operate UAV's. LIABILITY.. This is what drives our existence.

I have an A&P, started out working with guys who had been on similar pay scales with drivers in the 70's and 80's.

Cheers to the Airman Pilots who have been successful in negotiating great wages.

What I am getting at, to the point is piloting skills are forgone, procedure is priority despite your better judgment.

See "Slowing down in a crosswind" thread by username Hakeem on this current forum. Maybe the Mods could combine both threads seeing they are both on the subject of slippery runway crosswind landing technique?

Pod mounted engines only with turbo-jet engined aircraft, 727 and business jets. With business jets, there have been more than a few occasions of people going off the side of the runway when only one reverser deploys and the crew does not react quick enough. I saw a Westwind go off the side of the runway in Aspen one day because of that. Right reverser came out the left one remained stowed.

And a 'Hi ho Sliver' and off into a snowbank they go. Minor aircraft damage, but severe pilot ego damage. :p

I have a photo of a G-IV off the side of the runway in Vail due to the same problem, I'll look for it.

And when I was with the Marshal Service our only real Deputy US Marshal pilot managed to run a Sabre 80 off the runway into the grass, collapsing the nose gear before they stopped. But in this case one of the reversers was in-op and had been pinned closed. After this accident, we changed the 'One reverser In-op' procedure to pin both reversers closed.

There was really no reason to pin both, we always had problems with the reversers on the Sabre 80s. One just had to slowly add power after the working reverser opened. But, the weakest link has to accounted for, so the procedure was changed.

I feel better, now.
 

Thanks for the kind suggestion. I went to the doctor and am now
on medication. I feel much better. :O

Again, please show me in an authoritative document where it says
to do this.

For interest, on some DC9 runway testing years ago and operating in moderately strong crosswinds, the TP chose to use asymmetric reverse during accel stops and had no difficulty.

However, I think the line pilot is more at risk using asymmetric reverse than idle reverse with coarse rudder input ?

Crosswind Landings.
Also at http://www.skybrary.aero/bookshelf/books/871.pdf
Fig 6 and the associated text covers the principles – keep the thrust contribution symmetrical, particularly as the runway friction decreases.

Asymmetric reverse NO NO NO :=

Perfectly acceptable to operate the B737-800/900 with only one operating reverser, which would of course mean you have asymmetrical reverse thrust. There are no x-wind limits per se.

From my company's MEL:-

OPERATIONS (O)
NOTE: Thrust reverser deactivation can result in the illumination of the MASTER CAUTION and ENG annunciation when performing a Master Caution recall.
1. During rejected takeoff and landing rollout, use the operative thrust reverser normally and, use the rudder and brakes to maintain aircraft directional control.
2. For wet and contaminated runways, apply weight and V1 reduction by no reverse thrust option in the QRH.
3. For dry runways, no performance correction is necessary.

Just because something isn't mentioned in (M)MEL doesn't mean it doesn't matter.

From my understanding, if something is not listed (mentioned) in the MEL, it must be operational.

What I meant was, if a consideration for operation with a MMEL item isnt listed, it doesn't mean it isnt important.

So for the post before mine, although it listed 3 items for operation with a TR on the MMEL, it didn't mention Xwinds, but that doesn't mean that Xwinds may not be a factor when operating with a MMEL TR.

Even with an interpretation ‘it must be operational’, the absence of a subject or operational consideration in the MEL is not approval for absence of operational thought.

Too often, IMHO, pilots revert to a simplistic ‘SOP’ / ‘legal’ interpretation of documents without thinking about the issue. Of course thinking requires some basic knowledge of the subject, which unfortunately is often absent or has been biased by inappropriate speculation.

So from the gist of the discussion above, when / how would single reverse be used?
Personally I would not; and to avoid the ‘but if you really had too’ argument, there are few if any such situations which could not be covered by a pre departure decision. No go for crosswind on a 'dry' take off (RTO) – the Captain judges the value, and a 'dry' crosswind or wet/ contaminated runway for landing (EU operators may, in addition have to consider landing distance if reverse is credited on contaminated runways).

The MEL covers pre departure issues; what if there was an en route failure, is there similar operational advice in the QRH or is the issue entirely ‘operational’?

Just found...
 

Just found in the bowels of an old Airbus document which
is entitled "Getting to Grips with Approach and Landing
Accidents Reduction". It's an old document...the issue I
have is "Issue 1" published in October 2000.

Have a read....the subject of interest and discussion is
addressed toward the end of the many-page booklet.

In any event, it's a good read...the whole document is....

BTW, there may be an updated version of this. If someone
knows of such a revision, please let me know....I'll try to
find, download, and save.

I have had a quick read of it and the Airbus document is remarkably similar to the B737's FCTM.

In both cases they explain how in a X-wind situation, reverse thrust can be resolved into (basically) two vectors, the one we are interested for the purposes of this discussion is the "side force" component.

From the Boeing 737NG FCTM. (The Airbus document requires very similar techniques)

....... As the airplane starts to weathervane into the wind, the reverse thrust side force component adds to the crosswind component and drifts the airplane to the downwind side of the runway. Also, high braking forces reduce the capability of the tires to corner.
To correct back to the centerline, release the brakes and reduce reverse thrust to reverse idle. Releasing the brakes increases the tire-cornering capability and contributes to maintaining or regaining directional control. Setting reverse idle reduces the reverse thrust side force component without the requirement to go through a full reverser actuation cycle. Use rudder pedal steering and differential braking as required, to prevent over correcting past the runway centerline. When directional control is regained and the airplane is correcting toward the runway centerline, apply maximum braking and symmetrical reverse thrust to stop the airplane.


Neither manufacturer mentions using asymmetric reverse thrust.

safetypee wrote:-

Entirely your call as to whether or not you use a single reverser. The B737 allows dispatch with only one operational reverser, provided performance considerations are met. Having done a "couple of dozen" landings in various versions of the 737 (-100/200/600 excepted) in my experience it is a non-event.

Again 737 specific. There is no checklist for a reverse thrust failure whilst in flight. From a performance point of view adjustments to your landing distance, based on the number of serviceable reversers, are covered in the QRH/PI.

As ever operate your aeroplane in accordance with your company's SOPs

Unless AFM specifically allows messing with it for x-wind, I wouldn't consider assymetric reverse use.
Don't try this at home!
When I was a young chap in RHS of a caribou, skipper made a steep approach on a strip to avoid actual enemy ground fire. He selected full reverse pitch just before touchdown due we were already half way along the strip. Due to a fault, one prop stayed in forward pitch, with approx climb power, so it was an exciting ride from there to touchdown and for the remaining 700 ft.