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Unintentional XC

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Unintentional XC

Old 5th Feb 2013, 08:27
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Unintentional XC

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!

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Old 5th Feb 2013, 08:30
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Be warned about what exactly?
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Old 5th Feb 2013, 08:45
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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.
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Old 5th Feb 2013, 08:53
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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.
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Old 5th Feb 2013, 11:11
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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.

Last edited by Richard Westnot; 5th Feb 2013 at 11:17.
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Old 5th Feb 2013, 13:57
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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.
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Old 5th Feb 2013, 16:55
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http://www.commander.org/Bergcom/Tec...t%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

Last edited by Pilotage; 5th Feb 2013 at 16:58.
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Old 5th Feb 2013, 17:27
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Hi

2 kts over demonstrated is ridiculous 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
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Old 5th Feb 2013, 17:28
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Max demonstrated means "worst seen during the certification test programme". It has no other meaning.

P
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Old 5th Feb 2013, 17:50
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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.

Last edited by 'Chuffer' Dandridge; 5th Feb 2013 at 17:56.
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Old 5th Feb 2013, 21:12
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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.
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Old 5th Feb 2013, 21:21
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Because most of the GA fleet is over 30 years old and there is no motivation to do so.....
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Old 5th Feb 2013, 21:52
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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.
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Old 5th Feb 2013, 22:26
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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?
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Old 5th Feb 2013, 22:45
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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.
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Old 5th Feb 2013, 23:45
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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.
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Old 6th Feb 2013, 02:03
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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"?

Last edited by Slopey; 6th Feb 2013 at 02:04.
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Old 6th Feb 2013, 04:53
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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.

Last edited by tecman; 6th Feb 2013 at 06:10.
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Old 6th Feb 2013, 06:58
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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...
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Old 6th Feb 2013, 07:17
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"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

Last edited by Pace; 6th Feb 2013 at 08:37.
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