Touchdown with crab on slippery runways

[Driver170 42]

 

Touchdown with crab:

 

It is recommended to use this method when landing on slippery runways as it reduces drift on touchdown and allows for rapid deployment of the spoilers and autobrake as all main gear have touched down simultaneously. However, rudder and aileron input to de-crab after touchdown must be applied in order to maintain proper directional control.

 

This method is not recommended on dry runways with strong crosswind conditions as on landing the aircraft will tend to track upwind until the correct de-crab technique is accomplished. This lack of initial directional control is undesirable. Fly the nosewheel onto the runway after the aircraft is tacking the runway centerline.

 

I just can't figure out why its recommended on slippery runways and not dry runways?

[Bobsk8 12,489]

Touchdown with crab:

 

It is recommended to use this method when landing on slippery runways as it reduces drift on touchdown and allows for rapid deployment of the spoilers and autobrake as all main gear have touched down simultaneously. However, rudder and aileron input to de-crab after touchdown must be applied in order to maintain proper directional control.

 

This method is not recommended on dry runways with strong crosswind conditions as on landing the aircraft will tend to track upwind until the correct de-crab technique is accomplished. This lack of initial directional control is undesirable. Fly the nosewheel onto the runway after the aircraft is tacking the runway centerline.

 

I just can't figure out why its recommended on slippery runways and not dry runways?

 

I have seen in done on dry runways with all different types of airliners. Touchdown, on mains and then kick the nose over with rudder. 

[skelsey 765]

 

 

I just can't figure out why its recommended on slippery runways and not dry runways?

 

It tells you why:

 

 

 

It is recommended to use this method when landing on slippery runways as it reduces drift on touchdown and allows for rapid deployment of the spoilers and autobrake as all main gear have touched down simultaneously.

 

 

 

This method is not recommended on dry runways with strong crosswind conditions as on landing the aircraft will tend to track upwind until the correct de-crab technique is accomplished. This lack of initial directional control is undesirable.

 

(My highlights).

 

If you think about it -- on a slippery runway the reduced friction between the tyres and the runway will allow the aircraft to continue "drifting" sideways for a period after touchdown. On a dry, grippy runway, however, when you touch down in the crab the tyres will "grab" and the aircraft will want to start going where the nose is pointing (i.e. off the side of the runway).

 

That said, as Bob points out, in reality you will see all manner of crosswind techniques, some more questionable than others...

[Driver170 42]

Right cheers guys. Think i'm getting a grasp of it!

 

Simon - If you land in the crab on a slippery runway, will the aircraft not keep on sliding sideways off the runway? Will it not be easier to control on a dry than a slippery?

[Bobsk8 12,489]

http://www.flaps2approach.com/journal/2014/6/17/crosswind-landing-techniques-part-one-crab-and-sideslip.html

[skelsey 765]

 

 

If you land in the crab on a slippery runway, will the aircraft not keep on sliding sideways off the runway? Will it not be easier to control on a dry than a slippery?

 

When you're in the crab, the nose is pointing upwind, but the aircraft is travelling in the direction of the centreline (because of the drift). When you touch down, the tyres will slide on the slippery surface and the aircraft will continue to travel along the centreline (obviously as the aircraft slows and the tyres start to grip you will eventually need to point the nose in the right direction, as the FCOM says).

 

On a dry runway, as I say, because you have more grip if you touch down with the nose pointing off-centreline, rather than skidding the tyres will grip immediately and want to start taking you wherever the nose is pointed.

 

Bob's link provides a good summary of the techniques.

 

Just as a small point -- Bob used the term "kick off the drift", which is a is commonly used but IMO slightly misleading phrase as it implies an aggressive application of rudder. FS aircraft are a little variable in the way in which they model yaw-induced roll, and I'm not sure what the NGX is like in this regard, but if you "kick" the rudder in a real jet you are likely to get a very alarming roll (in the "wrong" direction in the case of a crosswind landing) -- the rudder is a big, powerful control surface.

 

I personally would argue that you never "kick" or "boot" the rudder - you apply rudder pressure. To that end, I prefer the term "squeeze" off the drift, which I feel is a better description of what you're actually doing  :wink:.

[downscc 1,327]

 

 

I personally would argue that you never "kick" or "boot" the rudder - you apply rudder pressure. To that end, I prefer the term "squeeze" off the drift, which I feel is a better description of what you're actually doing

 

Agree, even in a light twin there's no kicking or rapid rudder deflection...that's just not intuitive when you're in the cockpit. A gradual application of correction just looks so much prettier LOL

[robert young 2,897]

Agree, even in a light twin there's no kicking or rapid rudder deflection...that's just not intuitive when you're in the cockpit. A gradual application of correction just looks so much prettier LOL

 

Here's a BA 747 landing in quite a marked crosswind. The pilot reduces the crab just before touchdown with a lot of rudder into wind so the sideways strain on the landing gear is minimised. Pretty good I'd say.

 

 

[Spin737 102]

Also, it eats up tires if you land on a dry runway with drift.

[downscc 1,327]

 

 

The pilot reduces the crab just before touchdown with a lot of rudder into wind so the sideways strain on the landing gear is minimised. Pretty good I'd say.

 

I am surprised that he kept the nose gear up for a couple extra seconds. I was taught to get all the rubber on the road expeditiously in a stiff crosswind; however, considering he already has lots of rubber on the pavement with the mains I guess the nose wheel isn't adding that much resistance to lateral movement. Interesting.

 

My favorite crosswind arrivals are in the B52, which cannot drop a wing to cross control coming out of the crab. It has steerable main gears, set by the pilot during approach to allow the aircraft to roll forward with the fuselage at an angle to direction of travel. That is amazing to see.

 

My problem landing is when there is no crosswind LOL... here in Corpus Christi TX a normal day has at least 15 kt crosswind component coming at ya and I've seen 43 kts off the nose 30 deg, (22 kt crosswind component)  one gets so used to it that when it's calm the touchdown tends to be ...., shall I say aggressive.

[Bobsk8 12,489]

Agree, even in a light twin there's no kicking or rapid rudder deflection...that's just not intuitive when you're in the cockpit. A gradual application of correction just looks so much prettier LOL

 

I mean't kicking out the crab, not stomping on the rudder like the Airbus Pilot did climbing out of JFK and tearing the plane apart..  Cheez.......

[Driver170 42]

Like always great explanation simon makes sense and thankyou all for helping me out.

Also, it eats up tires if you land on a dry runway with drift.

 

Very true

[hesynergy 67]

I mean't kicking out the crab, not stomping on the rudder like the Airbus Pilot did climbing out of JFK and tearing the plane apart..  Cheez.......

Zakly when was that bob? Can't find any references ....

 

Chas

[19dcavscout 39]

Zakly when was that bob? Can't find any references ....

 

Chas

American Airlines Flight 587.  The crew repeatedly use full left and right rudder and caused enormous stress on the airplane tearing the rudder off.

 

http://www.ntsb.gov/investigations/AccidentReports/Pages/AAR0404.aspx

[Chris Crawford 49]

Zakly when was that bob? Can't find any references ....

 

Chas

 

Was over a decade ago. It was an Airbus A310 or something like that.. Got caught in windshear on takeoff and tried to use the rudder to get out of it, but it put too much stress on the aircraft, and the tail ripped apart in flight. At least that's what I think what happened.. What he was doing wasn't exactly wrong, it was just wrong for that type of aircraft. I believe he flew C130's before, and that was actual the correct method of exiting windshear on that type of aircraft. But, the C130 has a much, lets say, "stronger" tail and rudder section, that could handle that kind of stress.