Is it worth pointing out (as the Maule flight manual does in plain English) that “demonstrated crosswind” is not a limitation?
You don’t fly twins in 600m, so it will be hard to test the best technique ;)
You fly them into limiting runways; the absolute length is not the point.
A Cessna 421C does 600m easily.
From what I learned from an old beech service engineer, during certification the test pilot was required to ‘demonstrate’ cross-wind capabilities using ‘average’ pilot techniques in front of observers; he was supposed to land with no correction whatsoever, mainly demonstrating the strength of the landing gear.
Two factors mainly affect the ‘demonstrated wind capability’: the wind blowing at that moment with the observers present, and the strength of the landing gear.
The “demonstrated crosswind” is done for certification (to the aforementioned 0.2 Vs) by a manufacturer’s pilot, without applying unusual pilot skill or attention with the procedure described in the flight manual. If 0.2Vs is demonstrated, the aircraft passes that certification requirement, and that value may be entered in the flight manual. It is not a limitation on the aircraft, and may be exceeded by the pilot. Aircraft manufacturers are not going to enter a value exceeding the requirement of 0.2Vs, because it is not a limitation. There is no benefit to publishing a greater value than necessary, and taking liability for that, with no marketing benefit.
Peter wrote:
A Cessna 421C does 600m easily
600 meter runway length has been fine for me in a C310, C337, Islander, and Twin Otter.
Pilot_DAR wrote:
There is no benefit to publishing a greater value than necessary
… unless they are selling primarily into a market where the demonstrated crosswind component is treated as a hard limit, as has historically been the case in Europe.
I strongly suspect that that was the driver for Socata demonstrating a 25kt crosswind component for the TB20.
Jacko wrote:
Is it worth pointing out (as the Maule flight manual does in plain English) that “demonstrated crosswind” is not a limitation?
Yes, that’s one thing that kind of makes me go ‘gnnngghhg’, when I hear someone saying “you’re a test pilot if you exceed the maximum demonstrated crosswind”, as if you’re exceeding a limitation and doing something terribly dangerous. That and “slips with flaps are never allowed”.
Didn’t fly the day this photo was taken.
Wasn’t happy with 30G50 right across the 600×20m grass strip.
Cobalt wrote:
… unless they are selling primarily into a market where the demonstrated crosswind component is treated as a hard limit, as has historically been the case in Europe.
I have heard this, though not with absolute legal certainty. Of course an authority (EASA) can impose further restrictions on the operation of aircraft, but one must consider the mechanism by which that is enacted. For a larger airplane, it will be a different flight manual, with different wording or limitations than the original aircraft was certified with, and often a different aircraft model designation. The Jetstream 4100 was sold in a model variant (which was the one not approved in Canada) with a different flight manual, and limitations, though otherwise the same plane. The Twin Otter had a different variant for the UK market, again, different flight manual and limitations, -same plane. That said, I can’t see the inertia to start creating different flight manuals for GA types in different nations. The only thing which comes close is that in the USA, the Cessna 206H floatplane is a six place plane, in Canada, it’s only a five place. I don’t recall how that is enforced.
As for “demonstrated” crosswind, generally, you’ll notice that the published value is NOT in Section 2, Limitations, but generally in Section 5, performance. For the 172S, for example, its with the “Wind Component” chart, and it says: “NOTE: Maximum demonstrated crosswind velocity is 15 knots (note a limitation).”. I think Cessna wants you to know that it’s not a limitation! If an authority wants to make it a limitation, they must find a regulatory way of communicating that to the pilot (different flight manual, placard by AD etc.). If the authority, is silent on the topic, but the flying school want’s to impose the “demonstrated” as a limitation, well, I suppose they own the plane, they can limit it’s operation as they wish. I am aware that the DA-20 does express crosswind as a limitation in Section 2. They’re no required to make this value a limitation, but if they chose to – it is.
Exceeding any limitation is bad. Exceeding a demonstrated capability is okay, if you have the skill.
The background of not making crosswind a limitation is: If they do, and you know that the value is higher, you are prohibited from attempting a landing under those conditions. So, if you can’t fly to an alternate with more favourable wind conditions, what ar you supposed to do, wait up there? “Yes, Mr. EASA Inspector, I crashed, ’cause I ran out of gas, ’cause I was abiding by a landing prohibition for crosswind, waiting for it to subside.”. EASA would not look good. Instead, attempt the landing, it will probably work, and even it it does not, it’ll still work out better than a forced landing, ’cause you ran out of fuel!
That flaps sideslip limitation for some 172’s is historical. It has been well documented. Only certain later ’60’s models needed it, but it was retained for the type, out of an abundance of caution. It comes from an unfavourable interaction of the wake off the outboard corner of a fully extended flap, to the stabilizer, making the stabilizer less effective. It’s sharp and surprising around 55 knots, but controllable. If it were not controllable, the plane would not have been certifiable. Note that the 150/152 have the same wings and flaps, just a smaller span, so the interaction is not the same, and the 15x does not have the problem. Similarly the larger Cessnas. The 170 and L19 have a different tail, so again, no affect – just certain 172’s. The 172’s which are okay, (though still placarded) have a larger dorsal fin, which seems to reduce the effect.
Peter wrote:
A Cessna 421C does 600m easily.
Not sure about easily? I think this is around the minimium on a SD with reasonable payload.
There arent many twins that will be comfortable with 600 metres. Of course the getting out is almost entirely a matter of physics, but getting it down in that distance requires the pilot to be on his game, on speed and no over run – there isnt a lot of margin. I find in most twins something around 750 metres is comfortable most of the time! Less than that and you had better get it all right. 
