Crosswind landing technique

[Aleks]

What is the correct procedure in real life for 747?

I am a lowly PPL-A and in DA40 I prefer to crab almost all the way and then kick it out right before touchdown vs. sideslipping. Gives me better control in gusty conditions.

On 747 do you have the same approach or do you land crabbed and then straighten the nose before touching down with nose gear? I have no idea how much crab the main landing gear can handle on 747 (0 on DA40).

[Jeroen Hoppenbrouwers]

Same as in the DA40!  Unless you are absolutely sure the runway is slippery.  Monitor an autoland; that is a good model.


Hoppie

[Mariano]

Aleks,

Our company 747-400 FCOM Limitations section states: "Sideslip only (zero crab) landings are not recommended with crosswind components in excess of 20 knots. This recommendation ensures adequate ground clearance and is based on maintaining adequate control margin."

The Boeing FCTM states:

"De-Crab During Flare
The objective of this technique is to maintain wings level throughout the
approach, flare, and touchdown. On final approach, a crab angle is established
with wings level to maintain the desired track. Just prior to touchdown while
flaring the airplane, downwind rudder is applied to eliminate the crab and align
the airplane with the runway centerline.
As rudder is applied, the upwind wing sweeps forward developing roll. Hold
wings level with simultaneous application of aileron control into the wind. The
touchdown is made with cross controls and both gear touching down
simultaneously. Throughout the touchdown phase upwind aileron application is
utilized to keep the wings level.

Touchdown In Crab
The airplane can land using crab only (zero sideslip) up to the landing crosswind
guideline speeds. (See the landing crosswind guidelines table, this chapter).
On dry runways, upon touchdown the airplane tracks toward the upwind edge of
the runway while de-crabbing to align with the runway. Immediate upwind aileron
is needed to ensure the wings remain level while rudder is needed to track the
runway centerline. The greater the amount of crab at touchdown, the larger the
lateral deviation from the point of touchdown. For this reason, touchdown in a
crab only condition is not recommended when landing on a dry runway in strong
crosswinds.
On very slippery runways, landing the airplane using crab only reduces drift
toward the downwind side at touchdown, permits rapid operation of spoilers and
autobrakes because all main gears touchdown simultaneously, and may reduce
pilot workload since the airplane does not have to be de-crabbed before
touchdown. However, proper rudder and upwind aileron must be applied after
touchdown to ensure directional control is maintained."

Best regards,

Mariano

[Aleks]

Thank you, gents.

[United744]

I think I read somewhere the MLG can handle a crosswind up to 7 degrees. You don't need to eliminate all of the crab angle; just most of it.

[Hardy Heinlin]

By the way, depending on the ground friction, the 747 tends to slightly decrab itself on touchdown (this is also simulated in PSX). As the main gear is aft of the aircraft's lateral center, the aft part of the aircraft (which has ground contact) starts decelerating earlier than the forward part which is still airbone. For example, if the aft part is right of the runway centerline and the forward part is left of the centerline, the aft part induces a clockwise turn. It's similar to the weathervane effect where the wind turns the vane until it's inline with the wind direction. In this decrab effect it's the ground friction which turns the aircraft until it's inline with the runway heading.