View Full Version : Crosswind Landings - Sideslip or Crab??


Mamakim
14th Jul 2006, 00:55
Hi All,

I tend to fly a crabbed approach in crosswind conditions all the way down final until its time to flare which I then kick it straight and then apply aileron in the correct direction.

1/2 the people in my company use the sideslip approach.

Just wondering what other people out there are using and teaching and why they are choosing one method over another.

Many thanks in advance to those who reply.....



hugh flung_dung
14th Jul 2006, 09:43
The "wing down" method wins every time unless the wings are long and low - it requires less guesswork and you find out early on whether you're getting near a limit.
Pax don't like being flopped-over for a long time so crab to a few hundred feet and then line-up with rudder and use bank to maintain centre line.

HFD

18greens
14th Jul 2006, 10:14
Doesn't everyone do both. The only question is when do you convert from Crab to Wingdown, top of climb, just before touchdown or anywhere in between.

homeguard
14th Jul 2006, 10:27
I believe that the wing down should not be flown on the approach but only applied during the hold off to the landing.
With regard to teaching the crab and kick straight for the touch it should be taught and practiced first for the following reasons;
A) Not all aircraft will allow the wing down method or at least are limited; long wingspan, short undercarriage, engine nacelle ground contact. Propellor ground clearance (many light twins). On some types the aileron will loose effect before the rudder during the hold off making it impossible to maintain the wing down.
B) The crab and kick straight method is always applicable either wholely or in part but is harder for the student to grasp and therefore should be taught early and be in the pilots armoury from the outset. The wing down when it is appropiate is very effective i agree but it can be taught very quickly at a later stage of training or during a subsequent type conversion.
C) A low hour student or PPL can become easily confused and lower the downwind wing with catostraphic results. We read of these accidents month by month.

unfazed
14th Jul 2006, 12:59
The crab and kick straight method is always applicable

Tend to disagree with the above statement

In a varying gusty approach the crab and kick straight method is more hit and miss than the wind down method.

Wing down on approach you can see what you are dealing with and make an early go around if necessary, with the crab and kick straight you are waiting until the critical moment to see if you have enough rudder authority to counteract the crosswind, also you are reliant purely on rudder authority to line up the aircraft - wing down gives you more ability to overcome a stronger crosswind. In very strong crosswinds you may well land with a sideways drift even with the nose lined up with the runway.

Mr Garrison
14th Jul 2006, 14:51
I always use crab and kick for these reasons:

Problems associated with a sideslip landing:

1. Airspeed indicator not aligned into the oncoming airflow. It is offset to the wind and a true representation of airspeed will not be reflected on the ASI leading to an underreading of approach speed which leads to a higher approach speed to the landing threshold.

2. When the aircraft is aligned with the landing runway, then the fueselage will cut out some of the airflow and thus will create extra drag because now aircraft is going sideways through the air pushing the main body of the aircraft through it. Due to the aircraft going sideways through the air, the downwind wing will now experience less airflow due to the blanketing of air from sideslipping which will in turn decrease lift.

3. Constant corrections are needed all the way down finals as in general, wind speed will decrease as the aircraft nears the ground due to surface friction and obstructions. This requires constant corrections.

4. More power will be needed because more drag is being experienced and therefore more power will have to be bleeded off during the final touchdown. This extra power reduction will have an effect on the slipstream properties from the propeller and therefore the amount of extra correction required from the pilot.

5. Uncomfortable for passengers

B2N2
15th Jul 2006, 00:56
I always use and teach a combination of both, crab on final, wing down over the runway.
Always thought the combination was easier to master then either method on itself.

GOLF_BRAVO_ZULU
15th Jul 2006, 01:09
On a Cessna 150/172 I was always accepted on slipped approach. On a microlight, I'm always hammered for it! Slip is great!

BillieBob
15th Jul 2006, 08:33
It's horses for courses - In over 35 years of professional aviation, I have never come across any commercial air transport operator that favours the 'wing-down' technique, for many of the reasons previously stated. However, the same imperatives do not exist in light (especially high wing) aeroplanes and so it comes down to personal preference. If you elect to employ the 'wing-down' technique, expect to have to change if and when you move on to bigger things.

kluge
16th Jul 2006, 04:49
homeguard - not sure I agree with your option (c). Lowering the downwind wing (albeit not vertical !) will cause the aircraft to be blown sideways making it very difficult to line up with the runway. Probably a/c dependant I should think.

The reason I am querying this is that a x-wind approach in a Pitts special requires downwind wing down and nose slightly into wind. I'm talking around 10 deg off runway centreline here with 5-10deg bank. Ok Pitts is a long nose short coupled tail tragger with lots of power.

A reversal to windward wing down takes place at the same time at flare to compensate for drift - of course you can't see out the front at this stage because of the nose hence head back and use peripheral vision to keep the a/c staight. It's wot the makes the Pitts fun.

Other benefit for slipping approach (x-wind or not) that seems to have been missed is that its an excellent and safe way to reduce height whilst maintaining airspeed and heading if high on final.

satpak77
16th Jul 2006, 05:21
if you are moving into heavy turbine equipment, get used to flying a heading off-set to accomodate the wind.

what do you do on a ILS, in the soup? you don't "kick it out" when you reach DH do you?

of course not

alot of that stuff is Private Pilot Cessna 152 stuff, you won't use it as you progress into bigger stuff

kluge
16th Jul 2006, 07:13
No thanks - 'bigger stuff' is not my idea of flying fun.

machlimter99
16th Jul 2006, 09:04
satpak77,

If you are flying a heading offset it means that you are aligned to the runway centerline however if there is a strong crosswind the aeroplane will still weathercock into the wind (i.e) appear to crab. So just by flying a heading offset just wont do. Thats why we are talking about these two methods.

Crab technique I feel is the best, however its interesting to note that when Boeings autoland they use the wing down method. Not sure about airbus.

homeguard
16th Jul 2006, 09:14
Kluge you refer to an approach wing down heading into wind. I presume you are refering to a straight in approach when as much as anything else you would do as you describe to see forward - I personally hate this technique although flown by many Pitts pilots. I prefer to fly the more traditional curving sometime sideslipping approach in a Pitts which gives me good sight of the runway all the way down to the hold off. C) is not an option but a fault.
Why are some claiming something special or different for the 'big boys'. Both techniques are applicable to some extent in all aeroplanes large or small. The earlier B737 and the B707(four engines) and many others are limited in wing down owing to the engine nacelles striking the ground. The later 737 models have flattenned lower surfaces to the engine nacelle to allow more wing down and therefore increasing the landing crosswind component. The crab in large aircraft can also be limiting owing to inertia (time taken to kick straight) at the touch. Therefore a combination of both techniques is used. Maximum wing down allowed with the minimum crab permissable which is why my earlier comment that the crab is always an important skill to have mastered.

kluge
16th Jul 2006, 09:40
homeguard - thx for comments. All downwind circuits require a curved approach on base/final in a Pitts for proper rwy alignment.Try a Pitts flight for the viz - or lack of - experience. For straight in approach slip either way for rwy centreline viz in which I agree with your comments. For x-wind in a Pitts (and MAYBE for other taildragger bipes) you kick nose off INTO wind which is different slideslip technique to a tri-gear. I made the mistake once (but a great learning experience) of trying the other way ie wing down into wind. No way I could hold rwy heading. Tried the approach twice and aborted. After 2nd time time I asked for in wind runway change (that was available as an option). Landed into wind (slideslipping for viz and x-wind not dependant) and did a greaser - in a Pitts. Only when I landed did I realise I did not do correct x-wind technique of nose into wind (we live and learn !) hence my x-wind approach screw-up.

Post aeros adrenalin let down and all that.

kluge
16th Jul 2006, 09:48
sorry homeguard - per your 2nd comment re the heavy iron 18 wheeler stuff I'm too interestd in the answer. I'm sure it is very different stuff to high power-to-weight aero a/c.

Crappy arvo weather in hK and enjoying LA Boudelle beer !

hikoushi
17th Jul 2006, 07:30
Well, it's not exactly heavy iron, but in the light-to-moderate-iron Dash-8 both methods work fine. I usually crab down final and kick it out in the flare, but with a very strong and / or gusty crosswind (especially on a short runway) I tend transition to the slip a lot earlier on final. With it's high wing the Dash can take quite a bit of wing down on landing, and with a touch of differential power when the crosswind component gets above 25-30 knots it handles very nicely (6.0 Richter scale touchdowns notwithstanding).

rons22
24th Jul 2006, 20:36
Isn't there a risk of wing dropping when you are low and slow? For example, do you recommend slightly higher speed on approach when you use wingdown technique?
I landed in few airfields where wind suddenly drops due to hangars or trees etc. If your wing is down and speed drops by 15kts, would you have enough rudder authority or wind flow over wings to straighten the wings?

theresalwaysone
31st Jul 2006, 01:23
Not quite correct about larger aircraft

I flew a large twin engined jet on scheduled service public transport and during auto lands at around 100 feet you woud feel it squeeze on rudder and put the into wing down. The other great thing about the aircraft is that it didnt have an opinion about which method was best. The best method is the one that allows you to land with zero drift and miss all the scenery!

BEagle
31st Jul 2006, 06:24
No-one should ever 'kick off' the drift on a 'crab' crosswind landing.

Some swept wing aircraft will roll very powerfully if high yaw rates are used when 'de-crabbing'. Hence a significant into-wind aileron deflexion may be needed.

I used to teach "aligh the aeroplane with the RW centreline at the same rate as you pitch in the flare; use sufficient aileron to maintain wings level as you do so". That stopped the 'bootful of rudder' merchants needing armfuls of 'opposite lock'; if they screwed that up they could end up drifting downwind before the flare. I had to take control from a VC10 student once who was on the downwind side of the centreline and drifting further downwind at 100 ft with no sign of correcting.... But the little bugger hadn't trimmed properly during the approach, so even full aft control column didn't really cushion the resulting firm arrival. This had all resulted from a 'low drag' ILS approach (180 to 4 DME), during the deceleration to VAT, more into wind 'crab angle' was needed to cope with the 15kt crosswind; he was confused by this and was still trimmed for 180 KIAS as we approached the ground at about 140......

theresalwaysone
1st Aug 2006, 12:13
No-one should ever 'kick off' the drift on a 'crab' crosswind landing.

....

Beagle as an airline pilot you should know that no one should ever kick anything on an aircraft except the first officer!