X-wind landings on airliners - slip or crab?
 

I am under the assumption that the gear of most airliners is able to withstand landing in crab up till max-certified x-wind component. Is that correct or is that only valid for slippery conditions?

I am not talking about preferred techniques, only what the manufactures recommend and what the aircraft can stand.

I know the 747 can land in crab but how about e.g. a 737, MD80 and Airbus 300, 32X and that size of aircrafts?

Hi Tor

in my MD80's AOM there's no reference about maximum crab angle the main ldg gear can withstand during landings.
Once someone told me that a 4 degree crab angle was maximum for a DC9 (but i doubt about this value!).
What i do is landing as straight as possible during a x-wind.(Low wing tec.)

Hope this can help

BTW thanks for your replay about the visual app. minima

B_D

I much prefer to crab then ease it straight or almost straight before touchdown 737 and A320. Slipping with the a/c out of balance just feels awfull. I gather on 747's etc, you need to be very carefull about the outboard engines so maybe a combination of techniques is needed. Anyone big a/c drivers care to comment.

If the landing gear is manufactured by Menasco, it will withstand anything...the best in the business. NEVER have seen a Menasco gear fail (except possibly nose gear, pilot f@ckup maybe), used on almost all Boeing, Douglas, Lockheed aeroplanes....don't know about AirBus.
But...expensive to overhaul.. for example, $365,000 on the TriStar...complete set.
But hey, built TOUGH.
Dowty in second place, very good product!
As in anything...you get what you pay for.... or... the quality goes in before the name goes on...

I guess the side load on the gear landing with crab would depend on just how hard it was planted. A greaser would be no sweat, but 12ft/ec at 20 deg mmmmmmmmmm

737 can withstand landing at full crab angle (35kts), but it has a castering main gear which absorbs the impact. Use the crab technique myself, would be concerned about scraping something with wing down, and pax. don't like it. Also, if x-wind from the left would touchdown on left gear and so no spoilers until right gear touchdown. Have landed with about 15kts of drift on. It isn't pretty but it just kinda skips and alligns itself with the runway.

The recommended Airbus way is to "use rudder to align the aircraft with the runway heading during the flare while using lateral control to maintain the aircraft on the runway centreline." Wing tip or engine scrapes at 18 degrees on A320/321 and 16.5 degrees on A330. So there's a bit of margin there.

I've found that all 3 handle quite well in crosswinds, particularly the A330 and A321. A330 - inertia does the job - no need for wing down. A320/321 - same again really, so long as you don't float too long then it's fine. IMHO, there's no "right" or "wrong" way - whatever lands your plane!!!!! :p

All th boeing a/c I've flown can land with all the drift offset( in the crab). But unless it's slippery you wouldn't do it.
The operator I fly for only accepts crab till after flare then kick ( for want of a better word) straight, keeping wings level. This avoids a pod scrape.

The DC-8 70 series (re-engined with CFM 56's) is particularly critical to bank angle in a crosswind landing (If I recall, pod strike was at 5.5-6.0 bank). So a combination/compromise of wing down, accept the crab is used. Pod strikes are not unusual on these aircraft.

The "large" twins are a handfull in a crosswind - very similar to flying a light aircraft. The vertical stabs on these aircraft are disproportionatly large for the airframe (something has to help if you lose 40,000+ pounds of thrust on one side at low speed - rudder alone would not do it) making them excellent weathervanes.

If you want to see some folks doing it the wrong way, take a look at:

http://www.aviationpics.com/app/app.htm

Long load at dial up speeds, but worth the wait.

Thanks for the replies.

To clarify a bit. What I am interested in knowing is the recommended pratices from the manufactures and what the aircrafts are certified for. Not prefered pilot technique or the actual physical limits of the gear.

Quotes from AOMs would be nice.

[ 26 November 2001: Message edited by: Tor ]

I put links for video clips, in mpg format, of two interesting landings on Hong Kong's Kai Tak airport in the following webpage. Enjoy :)

Kai Tak Landings

The 747 (Classic at least) can do an auto-land without de-crabbing at up to 23kts of crosswind.
Pretty rough arrival though ... (only done this in the sim)
The norm for the 747 is to de-crab as much as possible during the flare, as late as possible because you can't lower the upwind wing - It'll scrape a pod at around 8° or so bank angle.

My understanding of the crosswind limitations of any given aircraft (be it max allowed or max demonstrated) is that the figure derived is indicative of what the aircraft was able to withstand WITHOUT the test pilots employing ANY corrective action at touch-down.

Important to note that manufacturers DO NOT recommended emulating these results, but a nice insurance policy against hamfisted jockeys such as myself! :D

Hi Tor,

here is what my AOM (737-31S) says (i don't know if that's boeings procedure though):

2.8.53

Crosswind Landing

Two methods of performing crosswind landings are presented. There is the de-crab technique (with removal of the crab during the flare) and the crab technique. During crosswind conditions, the crosswind wind correction angle can be maintained to touchdown. From the pilots perspective the flight deck will be offset from the centerline when the main gear touches down on the runway centerline.


2.8.54 Crossind Landing Capability

Boeing demonstrations of crosswind capability were performed using normal landing configuration on dry runways all engines operating, and with one engine out. The resulting crosswind guidelines are shown in the table below:

Dry: 40kts crosswind (reduced in our OPS to 35kts)
Wet: 25kts crosswind
Contaminated/Degraded Braking: 15kts crosswind.

Reduce crosswind guidelines by 5 knots on wet and contaminated runways whenever asymetric thrust is used.
Crossind limitation are found in Part B chapter 1.1
Wind is measured at 10 metre tower height.
Landing on untreated ice should only be attempted when no melting is present.
The crosswind guidelines shown in the table above through analysis and piloted simulation evaluations. These crosswind guidelines are based on steady wind (no gust) conditions. Due to the difficulty in modelling gust magnitude, duration, frequency and direction, gust additive to these guidelines is not provided.


2.8.55 De-Crab during flare

The objective of this technique is to maintain wings level throughout the approach, flare, and touchdown though aligning the longitudinal axis of the aircraft with the runway. On final approach, a crab is established with wings level to maintain the desired course. Just prior to touchdown while flaring the aeroplane, downwind rudder is applied to eliminate the crab and align the aeroplane with the runway centerline.
As rudder is applied, the upwind wing will sweep 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 simultaneously. Throughout the touchdown phase upwind aileron is utilized to keep wings leve.


2.8.56 Crab

On very slippery runways the crosswind crab angle may be maintained to touchdown. This will reduce drift toward the downwind side when touching down. Since the aircraft does not have to be decrabbed, pilot workload is reduced. Proper rudder and upwind aileron must be maintained to ensure directional control is maintained.
On slippery runways, crosswind capability is a function of runway surface conditions, aeroplane loading and pilot technique.
The aeroplane can land using crab only (zero side slip) up to the landing crosswind guidelines in the table on the previous page.

That's all about crosswind landings in the AOM. You can even use the wing-down technique in moderate crosswind (up to 9° of bank at around 5° pitch up).

Thank you for the detailed answer, Denti.

http://www.aviationpics.com/app/mal.jpg

:eek: :eek: :eek:

The VC10 has avery low wing and the great big flaps (ooh err!) get pretty close to the ground. Therefore, the crab technique is very much the preferred option (and I expect that to hold good for most airliners). As an aside, for landing in gusty or very strong x-winds landing with one less stage of flap (APProach, rather than LAND) gave better ground clearance (just in case) and better roll control with the 5kt faster threshold speed.

I understand the Hercules has to land using the wing drop technique (low sideways stress on the gear - but you can drop it straight down from a great height). However, with the high wing, flap/prop strikes are almost impossible!

Denti, one further question. I would be interested in hearing others opinion too.

How would you interpret your AOM? Is it allowed to land crabbed on a non-slippery surface with a 737?

According to the information we got from Boeing it is allowed to land in full crab up to 40kts crosswind on a dry runway. I have done that myself (okay, only up to 30kts or so). You have to be aware to align the plane with the centerline before landing the nosegear though.

[ 28 November 2001: Message edited by: Denti ]

Good 'ole Menasco gear .....again. Built TOUGH! (No, I do not own stock in the company...). On second thought...wish I did.