Crosswind/windshear Techniques

[Anti-ice]

I am curious as to what technique/practices are used when landing in a crosswind ?

Is it purely directional and what control surfaces are primarily used?

Also what actions are borne in mind and used during strong gusts and possible windshear scenario's?

Is there a higher speed threshold and decision height?

Also any interesting experiences ? !

[Too Few Stripes]

There are various techniques for landing in a crosswind and more often than not the exact technique is one of personal preference. However, successfully landing in a crosswind will involve using all control surfaces: elevator to control the roundout and flare; rudder to align the aircraft with the runway; ailerons to prevent wing lift on touchdown.

Windshear however is much more interesting, a crosswind is relatively easy to deal with if it is stable and constant but windshear, whether vertical or horizontal, is much more of a dynamic situation.

To give you an idea of recommended windshear actions I will quote from 'Pilot Windshear guide' a Boeing publication written on a FAA contract.

[QUOTE]Flight path must be controlled with pitch attitude (along with simultaneous full thrust application). Unusual stick forces may be required as a result.

Lower than normal airspeed may have to be accepted. Flying at speeds below normal reference speeds may be required at some time during the recovery to utilize the full performance capability of the airplane.

IT IS VITAL TO RECOGNIZE THAT SOME MICROBURSTS CANNOT BE SUCCESSFULLY ESCAPED WITH ANY KNOWN TECHNIQUES./QUOTE]

Disclaimer: This info is intended for Boeing, Douglas and Lockheed aircraft, use of this info on any other aircraft may result in improper aircraft operation!!!

Cheers,

TFS ;)

[Anti-ice]

Thank's TFS for your time and reply , interesting reading ;

I also wondered why the A320 family seem to yaw so much more than a boeing aircraft ?

[411A]

Add "wet/slippery" condition of the runway, and the directional control problems associated with thrust reverse....and the situation can become...quite interesting indeed.

[Pilot Pete]

Crosswind

The technique that I was taught for the 757 was 'wing down' which was something I had been told was 'never' used on 'big' aircraft at training school!!

The technique requires, as always, a stable approach with the correct drift applied to keep the a/c on centreline. At an altitude (personal preference) push out the drift with rudder and put the into wind wing down using aileron to conteract any drift. I usually do this by 200ft to get the feel before touchdown. It will require a slight increase in thrust to maintain airspeed (due to the increased drag of deflected control surfaces). The wing is only down a few degrees and it is kept down until touchdown (on one maingear before the other). The nosewheel is flown on and the into wind aileron deflected to keep the upwind wing firmly on the ground.

As for windshear........just finished the sim today with a mod/severe windshear recovery at rotation. Windshear had been reported, so the first decision would be not to depart......but being the sim we were to go! No reduced thrust being used in the circumstances. After the call of V1 the airspeed stopped increasing thus Vr was not reached. The procedure is that the PNF calls rotate by 2000ft from the end of the runway (you are committed of course since you do not have enough runway left to stop on). At this point the PF rotates to the all engine T/O attitude (calculated prior to T/O) and up to the 'pitch limit indicators' if required with intermittent stick shaker to maintain a positive rate of climb, ensuring max thrust is applied. This gives the best possibility of becoming airborne. Boeing recommend turning off the Flight Directors. It is then important to keep the pitch angle and fly through the windshear with the PNF calling any airspeed and vertical speed deviations. What can happen is the speed stays very low (negative wind component) and then changes rapidly to an increasing airspeed as the winshear is climbed out of. The configuration remains as set throughout, ie gear still down and flaps still in the T/O setting. Boeing recommend flap 20 if departing into known windshear conditions. The thrust remains at max unless the flap limit speed is approached at which point it is 'aggressively' controlled, both off then back on (autothrottle having been disconnected), until the W/S is passed at which point the gear would go up, climb thrust can be set and the a/c cleaned up on schedule. Finally after T/O checks and handing out of fresh underpants.

Fun.

PP

ps Forgot to mention landing in gusty conditions we add airspeed to our 'Vref' (threshold speed for a/c weight and config) using half the steady headwind component plus all of any gust factor up to a maximum additive of 20kts, bleeding off the gust in the flare. If using autothrottle for the landing (autoland) we just add 5kts to the Vref). Landing in windshear is not a likely course of action as the PF would elect to go around. Anyone who flies into Tenerife South will tell you what its like! The wind changes quite often late in the approach (especially with a wind greater than 20kts). What happens is the airspeed starts to increase markedly and the reaction is to reduce thrust. It depends on how far down the approach you are as to weather you can remain at low thrust (bearing in mind spool up time in the event of a go around). At the same time you need to put the nose down to keep on the glide and can end up in an undesireable, unstabilised scenario of low pitch attitude, idle thrust and still 5-10kts above your desired airspeed. We aim to be stabilised at 1000ft and MUST be by 500ft otherwise we go around.

Hope this answers your questions.

PP

[Capt. Crosswind]

I'm told to post on this subject or forfeit my nom de plume.

Not much to add to what has been said , but here's a couple of points to consider.

* going from laying off drift to wing down, lead with rudder, roll in aileron.
You are now in a sideslip & note P/Pete's suggestion regarding power.
* all of the crosswind mishaps I'm aware of involved a contact of the DOWNWIND wing / outboard nacelle,because the pilot eased off aileron after touchdown.

PS Anyone aware of a x/w incident where the into wind wing/nacelle made runway contact ??

[Ignition Override]

Good comments.

If your plane has tail-mounted engines, using a large amount of reverse thrust can seriously limit rudder effectiveness on some jets. Some planes have slid off the side of slippery runways because of this.

[Shore Guy]

IMHO - The "large" twins with wing mounted engines require the most aggressive use of controls in a crosswind takeoff/landing. Reason - the vertical stab is disproportionately large for the rest of the airframe, to keep the aircraft tracking straight with loss of engine at low speed/high thrust settings. They are powerefull weathervanes.

Along those lines....therefore the stresses involved in deflection/bending moments on the vertical stab are greater in these aircraft. It will be interesting to see how much of this type of analysis is included in the final report (way down the road) on AAL 587.

[quid]

Pilot Pete-

Are you taught to bleed off the "gust" additive in the flare, or the steady-state?

[Anti-ice]

EXCELLENT reply's guys, thanks for all your time and input , it makes you realize how much is really put into the training and practices of these demanding conditions .

[Capt. Crosswind]

Is anyone aware of a x/w incident due the 'into wind' wing/nacelle contacting the runway ??
From my experience & knowledge of incidents it has always been the 'downwind' wing/ nacelle making contact.

Shore Guy
Very interesting point you have raised - could we hear from the
structural/stress boffins on this subject ?

[Pilot Pete]

Quid

You are indeed correct sir, my mistake, long day watching the baby (well that's my excuse), or else it could be the reason why I keep 'thumping it on'!!!:D

PP