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highflyer9790
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Cross Wind Landings/airliners

Wed Jun 02, 2010 4:14 am

hi all,

after seeing numerous videos and photos of airliners landing in cross wind conditions, it seems as though it is not common practice to correct for the crab before touchdown and touchdown on the upwind wheel first, etc.? Many GA planes crab until short final and then input some sort of corss wind correction to make sure the longitudinal axis is aligned with the centerline at touch down...but ive been seeing many airliners taking quite the side load!

Any insights?

thanks,

Highflyer
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Starlionblue
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RE: Cross Wind Landings/airliners

Wed Jun 02, 2010 4:40 am

As I understand it, airliners can indeed take much more side load than GA aircraft.

Also, underwing engines mean that wings must be pretty level.
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411A
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RE: Cross Wind Landings/airliners

Wed Jun 02, 2010 4:58 am

Quoting Starlionblue (Reply 1):
Also, underwing engines mean that wings must be pretty level.

Only on some aircraft.
Example.
The L1011, in the normal landing body angle (9 degrees), is landed in a crosswind using the wing-down method, and...if the pilot gets a bit carried away, and gets the upwind wing waaaay down, the wingtip will strike the runway before the engine pod will.
 
PGNCS
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RE: Cross Wind Landings/airliners

Wed Jun 02, 2010 7:35 am

We do not intentionally land in a crab on any of the aircraft I have flown. That's not to say it doesn't happen, but we generally try to end up with the upwind wing slightly down. Don't overdo it, though, because you can hit something, e.g. wingtip, landing light (DC-9/MD-80), engine pod....

The landing gear are extremely robust on jet transport aircraft, though an engineer would be needed to explain the details of the loadings they are designed to take.
 
Dogbreath
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RE: Cross Wind Landings/airliners

Wed Jun 02, 2010 9:47 am

Can't speak for all other airline pilots and their airline's SOP's, however my airline, myself and most of the other pilots I fly with will never de-crab until the flare. You can get away with de-crabbing a small GA type aircraft, but an airliner with hundreds of PAX it'd be rather (no make that - very) uncomfortable in the back.

Depending on the severity of the crosswind, I fly crabbed to hold the centreline (or maybe just slightly on the upwind side of centreline) and then in the flare ease the rudder in to return the aircraft centreline with the runway's centreline. Of course a little aileron is required to prevent the upwind wing from rising too much. If all goes well you land in a wings level attitude and pointing down the runway on the centreline.
In very strong and gusty crosswinds I personally don't take out all the crab, but it all depends on how it feels on the day.
Also on wet or contaminated runways with lots of crosswind, I leave the crab in as this reduces workload and ensures a touchdown on the centreline and immediate operation of spoilers and autobrakes.

As PGNCS says, the landing gear are built to take the stresses of a touchdown in a fully crabbed axis (see the YouTube video's of Boeing testing the B777 in crosswind landings) up to the maximum certified crosswind limits.

To me the hardest part of a crosswind landing is not the approach, flare and touchdown, but the landing ground roll afterwards. The objective is to maintain the centreline and obviously decelerate the aircarft to taxi speed within the useable length of the runway safely.
After touchdown the crosswind is now pushing on the rudder surface wanting to point the aircraft back into the upwind corner of the runway and is also wanting to lift the upwind wing. Now we can cross-control by applying upwind aileron and appropriate rudder to maintain centreline (which for me is mentally thinking about wanting to steer for the downwind corner of the runway end).
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soon7x7
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RE: Cross Wind Landings/airliners

Fri Jun 04, 2010 2:46 am

Quoting DogBreath (Reply 4):

To me the hardest part of a crosswind landing is not the approach, flare and touchdown, but the landing ground roll afterwards. The objective is to maintain the centreline and obviously decelerate the aircarft to taxi speed within the useable length of the runway safely.

Watching the 747's on strong x wind days is always exciting. As you state...after runway contact the real job is to get the aircraft stabilized as your still moving fast enough that their is a real good chance the upwind wing, once all gears are on the ground is gonna get too much air under it. The 47 seems to really struggle with this while other models seem to penetrate ground effect better. I was watching the A380 come in to JFK with 80 degree x winds from the left and that giant billboard fuselage really doesn't bode well for x winds...not from I could see...  Wow!
 
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Scooter01
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RE: Cross Wind Landings/airliners

Fri Jun 04, 2010 7:56 am

Quoting highflyer9790 (Thread starter):
Many GA planes crab until short final and then input some sort of corss wind correction to make sure the longitudinal axis is aligned with the centerline at touch down...but ive been seeing many airliners taking quite the side load!

I guess many GA are piloted by their owners, and savings on tirewear might be a factor  dollarsign 

Scooter01

[Edited 2010-06-04 00:59:10]
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lowrider
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RE: Cross Wind Landings/airliners

Fri Jun 04, 2010 8:35 am

In light to moderate crosswinds, I will normally try to de-crab in the flare. When the crosswind component gets above about about 20 knots, I will go ahead and land in the crab. At that point I would rather get the mains on the centerline and don't want to risk a pod stike for the sake of style points. The plane can handle it.
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zeke
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RE: Cross Wind Landings/airliners

Fri Jun 04, 2010 1:30 pm

Quoting highflyer9790 (Thread starter):
Many GA planes crab until short final and then input some sort of corss wind correction to make sure the longitudinal axis is aligned with the centerline at touch down...but ive been seeing many airliners taking quite the side load!

The Airbus recommended technique for crosswind landing is :
- apply rudder to align the A/C on runway center line
- act on the stick (on the opposite direction) to maintain the A/C on the center line, with possibly very slight wing down into wind.

In strong crosswind, a full decrab might lead to a significant into wind aileron input leading to a significant bank angle. The pilot must be aware that there are aircraft geometry limitations in pitch as well as in bank not only to prevent incurring a tailstrike but to prevent scrapping the engine pod, the flaps or the wing tip.

In such conditions a partial decrab is preferable.

The A330 has a maximum demonstrated crosswind for landing of 40 kt, and the A343 is 41 kt. With a 40kt crosswind the full decrab may require above 15 degrees of bank angle, whereas a partial decrab (20 degrees crab angle remaining) requires only 5 degrees bank angle.

So you will see most airliners doing a partial decrab to prevent scrapping the engine pod, the flaps or the wing tip. The frew high wing airliners like the BAe-146 do not have this issue.
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