Unintentional XC

[ChrisA87]

Rockwell Commander 112a at an airfield in the Southeast. Attempted landing last week with a crosswind component of 14kts (apparently the handbook limit is 12kts). Veered off the runway where the nose wheel collapsed and probably caused additional unseen damage.

Be warned!

http://i.imgur.com/VJDaeJA.jpg

[S-Works]

Be warned about what exactly?

[mad_jock]

I dodut very much it is a limit it will be a max demonstrated.

And I have seen them lad in 20knts of xwind I will admit though the pilot wasn't a 100hour PPL.

[piperboy84]

Its probably not out side the planes capabilities as MJ said the limit is "demonstrated" but perhaps outside the pilots personal capabilities/tolerances. It's a pity he never went for an alternate, it looks like a really nice plane.

[Richard Westnot]

I have seen many undercarriage collapses. 20kts into wind. Even nil wind etc etc.

I sincerely hope that this discussion doesn't digress along the lines over being 2kts over the crosswind component in a perfectly capable aircraft.

Any pilot, even freshly minted who cannot fly safely in a crosswind of 14kts shouldn't really be flying.

I suspect that this was just a mechanical failure, that would have happened in any event, if not detected prior by the maintenance organisation.

The additional unseen damage will be a engine shock load inspection for starters.

[Johnm]

12kts certainly isn't a limit, the limit is when you run out of rudder authority. 15 to 20kts cross wind is fairly commonplace in Channel Island landings especially in Alderney.

[Pilotage]

http://www.commander.org/Bergcom/Tech/Documents/112A%20Flight%20Manual.pdf

On page 19 it does indeed give a "maximum demonstrated" crosswind value of 12 knots.

That seems very low; I've certainly landed similarly configured PA28s in considerably greater crosswinds, and would not regard that as a hard limit. I would take it as advice that I need to take particular care during the landing.

Also, the photograph seems to indicate a nosewheel collapse on a rough grass surface. That implies either the aeroplane was landed on its nosewheel, or it hit some kind of hole. Overstressing due to skidding sideways on a mishandled crosswind landing should break the maingear on one side. The maingear looks fine.

So, I'd guess either a mishandled landing, or a mechanical failure. Statistically the first is rather more likely.

P

[Pace]

Hi

2 kts over demonstrated is ridiculous :ugh: I am not saying this as a brag but as an example as I have over 2500 hrs on Seneca Fives (Not flying them now)
I landed one into Denham a number of years ago with a constant 40 kt cross wind 90 degrees across the runway.
That was the limit! Take my word for it! Over twice the demonstrated!
30 minutes later the airfield was closed in snow blizzards and the M25 ground to a halt!
So demonstrated ???

Pace

[Pilotage]

Max demonstrated means "worst seen during the certification test programme". It has no other meaning.

P

['Chuffer' Dandridge]

where was the picture taken?? (edited to add I've worked it out as Lee-on-Solent)

The only reason aircraft 'veer' off the runway is down to pilot incompetence or mechanical failure.. Nobody else to blame. If it's beyond the pilot's capabilities to keep it straight in that x/wind, then maybe he/she shouldn't have been airborne.

[abgd]

Why do they not re-visit the crosswind certification when an opportunity arises to certify for a greater crosswind component? It's not as if winds of 15-20knots are uncommon.

[S-Works]

Because most of the GA fleet is over 30 years old and there is no motivation to do so.....

[taybird]

Because most of the issues with crosswind limits are the limitation of the pilot, not the aircraft. Not always true, but more often than not. Increasing the stated figures in a manual does not give the pilot better handling skills, just more opportunity to get into trouble.

Note that the max demonstrated crosswind given in some manuals relates to the maximum demonstrated by a skilled test pilot who will have exceptional handling skills. It could be argued that these skills may be somewhat offset by what might be very few hours on type. This is more true for funky unusual types rather than the tried and tested trainers such as PA28s and C150/152 types.

In some cases crosswind limits are hard and can be quite low for demonstrable aerodynamic reasons, such as airframe blanking, or control authority, or for physical reasons such as undercarriage resilience to side load.

Whatever the case a) the limits (recommended, demonstrated, or fixed) are there for a good reason and b) your limits may not be the same as those listed, both above and below. But know which limit you're working to, and don't exceed the wrong one...

Just in my opinion, of course.

[Whopity]

Why do they not re-visit the crosswind certification when an opportunity arises to certify for a greater crosswind component? Clearly you have no idea what the Demonstrated X-Wind means. Would you like them to certify it on everyday of the week because you didn't think Thursday was sufficient?

[Contacttower]

I don't see how a 14kts crosswind, in of itself, could cause an aircraft like a Commander to simply veer off the runway. Similarly it seems unlikely the mere act of veering off the runway would cause the nose wheel to collapse unless it hit something really hard...or indeed soft and dug into the ground.

Looks more like a bad landing or a pre-existing mechanical fault.

[abgd]

Whopity, my understanding is that the demonstrated crosswind means that during the certification process a test pilot landed the aircraft successfully at that windspeed as confirmed by ground instrumentation. There is a minimum crosswind of 0.2 Vs0 that must be demonstrated for certification purposes, but there is no maximum limit on the crosswind component that may be demonstrated.

As Taybird pointed out, the limit may be real - in that nobody could land at a greater crosswind without breaking the aircraft - or it may be that the aircraft can land in much stronger crosswinds, but nobody has demonstrated this officially.

I guess this latter case surprises me because I would have thought that crosswind capability would be an important factor for anybody trying to buy an aircraft and it surprised me that manufacturers might not try to obtain the best figure possible. Secondly whilst I recognise that it is not a 'limit' in the same way as Vne, I don't recall reading any guidance regarding structural versus aerodynamic versus sane crosswind limits for the aircraft I have flown and in the absence of this information how is a pilot to know whether landing slightly above the demonstrated limit is in fact sensible?

Now, my understanding is that certification isn't easy or cheap and can't be done in a day, so when I see a C152 with a demonstrated crosswind capability of 12 knots, it strikes me that the test pilots must have had the opportunity weatherwise to obtain better figures, and it still baffles me that they didn't.

If you can't be civil, at least be constructive and point out to me where my misunderstanding lies.

[Slopey]

If a highly skilled test pilot landed it once in a 40kt crosswind, and they put that in the POH, how long do you think it'd take before someone in the US sues when they park it in a field with a 35kts xwind, due to their lack of handling skills, because "the book said the plane could do it"?

[tecman]

I chuckled a bit at the OP's open-ended warning because there's a Commander based semi-permanently at my home field here in West Oz. If the owner waited for the cross-wind to subside below 12 kt, he might never get it on the ground, especially this time of year.

Can't add anything to the correct comments regarding formal x/w certification but one practical point is that, not infrequently, high winds come with large guests which can influence how well an average pilot can handle the aircraft. When I was learning to fly, a steady x/w was not a particular challenge; keeping on top of the gusts is what required practice. Nowadays, I notice this effect with many PPLs and recreational pilots, especially those who fly infrequently. So, in a practical sense, a modest x/w specification may go some way to protecting pilots from themselves.

I do think there is considerable variation in the amount of optimism shown by manufacturers. For example, there's no discernable difference between what one can do in a C150 vs a P2002. In the latter case, though, Tecnam have a book value of 22kt x/w. The aircraft indeed handles well to beyond this limit but, especially with the no differential braking versions, landing with a strong left cross-wind will require nosewheel steering to become rapidly active if the weeds are to be avoided. The experience of having the touchdown speeds exactly right, anticipating reaching the limit of right rudder authority, and being ready with the central brakes is all part of learning about the aeroplane. From a manufacturer's viewpoint, it'd probably easier to just write '12 kt limit'. But I'm glad they didn't.

[Contacttower]

I mean the Bulldog had a demo figure of 35kts or something. I guess they didn't sell too many of them in the US...:E

[Pace]

"the book said the plane could do it"?

The book says many things in absolute detail that the plane can do! Hence why there are takeoff graphs etc.
The problem with winds are there are too many variables so getting close to that limit can mean you exceed it.
When I landed the Seneca the wind was constant 40 kts. I had no real intention of landing but more an intention to touch and overshoot a sort of have a look!
It worked out ok and I landed but in the back of my mind was that I would not be able to make a landing from it.
As stated that was over twice the demonstrated on the aircraft.

Demonstrated is more of a guide that the test pilot reckons the average pilot who is a PPL and probably does not fly every day of the week can safely handle with a good margin built into that figure.
ie you may have a demonstrated of 15 kts and that maybe the figure given to you from ATC but in the landing that wind may jump to 20 kts! No one has control over that.

Pace

[foxmoth]

I think those that are saying the manufacturers are right in accepting low crosswind values are wrong, Clearly you have no idea what the Demonstrated X-Wind means. Would you like them to certify it on everyday of the week because you didn't think Thursday was sufficient? if Thursday was a completely calm day with temperatures at -10 then they should certainly be certifying it on other days, it is SENSIBLE figures they should be aiming at, values given should at least be a guide and I would be very surprised if during the certification there not opportunities to demonstrate crosswinds greater than 12kts, whilst it would not be the ONLY factor in buying an aircraft, if I was buying I would be questioning why such a low figure and wondering just how strong the undercarriage is. The Bulldogs at 35kts is higher than really needed and I would not suggest that manufacturers should go out of their way to get high figures, but realistic ones should be achieved, 20 probably being one that should be easily managed in the time available.

[Pace]

Demonstrated as stated is just that but I do not for one moment think that is realistically the case.
It is surprising how many 15 18 kt days there are ;)
What happens if the aircraft is tested on a 25 kt day is that the figure the pilot puts in the book? I doubt it!
There will no doubt be a discussion and I am sure a lower figure would be selected depending on how tricky the aircraft was at 25kts.
The overriding consideration will be a fairly low timed PPL who does not fly that much while not selecting a figure which makes buyers think there is something wrong with the aircraft.
15kts will probably be used as a bench mark. If its tricky in wind the aircraft will be set lower if its good in wind a few kts higher!
Also into consideration will be the target market and experience of the pilots who are likely to fly the aircraft

Pace

[thing]

It was blowing a gale here the other day when I was at the club and we were talking about x wind limits etc. I mooted the point that say in the case of the Warrior which has a demonstrated limit of 17kts; although everyone is confident they could handle more than that, if there was a prang of some sort would not the insurance hawks say 'Well the weather at that time was 19kts across so you were flying out of limits therefore no pay out.' ?

[aluminium persuader]

As has been said before, "demonstrated" does not mean "maximum limit".

[Pace]

As Aluminium Persuader says demonstrated is not a limit which could be used against an insurance claim.

MTOW is a Limit and a proved overweight takeoff would mean a way out for the insurance.

One thing I am not sure of and no body has clarified is how realistically they come to a demonstrated figure?
I am sure its not the wind of the day the test is done as that could vary from 0 to 30 kts or above.
There must be a set procedure for arriving at a figure! My guess is its probably something along the lines I indicated in my last post but I do not know for sure?
Does anyone know how demonstrated is worked out?

Pace

[thing]

You would have thought they could work out absolute x wind limits on a computer these days. They can work everything else out on one.

I don't think there's even a demonstrated limit in the 172 POH, if I remember the wording correctly it's something like '15mph which the average pilot should be able to manage.'

[mm_flynn]

thing, foxmouth, etc.

I think you probably have an incorrect view of what manufacturers seek to achieve when certifying and marketing a general purpose aircraft.

Most punters are looking for speed, range, useful load, slick instruments, and a bit of style (note massive success of Cirrus).

Most manufacturers are looking to, meet certification requirements, have a manufacturing cost that allows them to make money and not set landmines to step on and get sued.

Given the certification requirement for crosswind component is a minimum number (i.e. they must positively demonstrate that the average joe can land in a crosswind of 0.2Vso) and almost no one seriously evaluates an aircraft on that number, why would they sweat it to go for a big number.

Now an aircraft marketed as a 'get in and out of the shortest, wildest, boulder strewn mountain strip with radical cross wind and turbulence' may well benefit from a massive maximum cross wind component and obviously rugged gear, but this is marketing as there is no certification requirement for how smooth or rough the landing surface can be.

[abgd]

Well, that may be so, but I'm sure I heard of an aircraft (? AT3) where 11 knots really was the crosswind limit where the tail ran out of authority. Perhaps I'm maligning the AT3, in which case I apologise to its manufacturers, but I remember reading about a flying school which really wished it had bought something else, because they lost so much flying time on that basis.