Cross wind limits - definitions please?

[Chucky_1]

Hi everyone,

with reagards to cross wind components. Is there by any chance a definition of; Maximum Cross Wind & Demonstrated Cross Wind Component.

Its just that in some Aircraft Flight Manual, I had seen a slightly higher component stating Max X wind Comp as Opposed to the Pilot operating handbook put out by the manufacturer showing a lower X wind component but stating its demonstrated

I once requested this from a CASA official in writing but he never sent it to me, I then moved on and did not worry about it, but the question has just came to mind again. :confused:


Chucky :O

[Old Smokey]

Chucky_1,

This is a quick one "off the top of my head" without reference to the books, so stand by for a better interpretation from other sources, John Tullamarine, where are you?

As you've mentioned CASA, I'll reply with their policy as stated to me by them 3 years ago which was when I last did an aircraft certification in Australia.

Maximum Crosswind Component is that which the manufacturer has determined is the most limiting, within the certification rules, as achievable for the aircraft.

The problem is that the Pilot's Operating Manual can only approve manoeuvres which have been actually demonstrated. Whilst the test pilot can "prove" values such as Vne, Vmo, Mmo etc. by flying there, crosswinds cannot be ordered.

Demonstrated Crosswind Component is the maximum which the manufacturer has test flown the aircraft to in the real world, and found it to be controllable. Therefore that is the limit which may be published in the Pilot's Operating Manual.

As a post script, I once flew an aircraft which had a demonstrated crosswind component of 37 knots, so that then became the limit, even though the manufacturer had determined that the aircraft would have been capable of a limit approaching 50 knots.

That's the 'blunt pencil' answer, standing by for much clearer 'sharp pencil' responses.

Regards,

Old Smokey

[Genghis the Engineer]

Maximum demonstrated is one of two things, and there's no easy way of telling which:-

(1) The maximum the test team could find during the certification flight test programme, and it was fine up to that, or...

(2) The test team went beyond that, but felt that this was a sensible maximum for pilots of average ability.



As for an absolute maximum, I'm not sure that such a term exists in the airworthiness regs. However, it is quite common for individual operators, be they airlines or flying clubs, to set a maximum permitted limit which they have decided is the greatest they want to see flown in their aircraft.

G

[john_tullamarine]

One needs to be a little careful, here.

Up until the adoption of OS NAA AFM/POH in lieu of the older style Australian manuals (eg for bug smashers .. to ANO 101.22), Australia adopted either the OS manual figure, whether a limit or demonstrated, or a locally determined figure, as a limit. Since the adoption of the OS manuals, the OS manual defines whether the figure is limit or (as is typical) demonstrated.

If chucky_1 has a specific, rather than a general, enquiry, he might like to email me and I can give him the appropriate CASA contacts to check on this week's policy. I don't know that the good chaps would thank me for publishing their direct contact details on PPRuNe .....

As to the terms, they mean what one would reasonably presume.

Design Standards prescribe that a suitable crosswind component be demonstrated and, if this is considered to be limiting, a limit should be declared. In practice, due to the difficulty and cost associated with chasing higher crosswind environments, the OEM often will not bother going beyond minimum acceptable crosswinds. Consider the minimum values specified at FAR 23.233 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=2268ccf8c5bfbb0390b849a912cefc20&rgn=div8&view=text&node=14:1.0.1.3.9.2.67.44&idno=14), FAR 25.233 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=2392ce79747963bd37dc71b90c65900f&rgn=div8&view=text&node=14:1.0.1.3.10.2.160.35&idno=14), and FAR 25.237 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr;sid=2392ce79747963bd37dc71b90c65900f;rgn=div8;vie w=text;node=14%3A1.0.1.3.10.2.160.37;idno=14;cc=ecfr).

"Demonstrated" means what was achieved during the certification flight test program, subject to meeting the Design Standard minimum values. "Limit" means that the TP considers the handling to be critical and, for sensible extension programs, the structures folk determine that the potential for pilot-induced structural loading is not overly excessive. I guess that most of us would equate "maximum" with "limit".

I've not seen too many troubles with "normal" aircraft .. however, the problems with unduly low figures which surfaced with some of the inter-connected control aircraft can be interesting when the inter-connection systems cause pilot difficulty at higher crosswind values. I can recall a local extension program for a family of quite nice little singles many years ago where the OEM crosswind was something like 13-15 kt and an intrepid team consisting of me and my TP mate gave it away in eye-opening "oh, isn't that interesting" at about 18 kt. However, at least it made the bird a bit more useful for the Oz market as we ended up with quite a few being sold to Oz interests. However, having flown quite a few bug smashers in crosswinds somewhat above the OEM demonstrated values, those particular models were examples of aircraft I wouldn't like to see in strong crosswinds ....

As to Chucky_1's main question -

Its just that in some Aircraft Flight Manual, I had seen a slightly higher component stating Max X wind Comp as Opposed to the Pilot operating handbook put out by the manufacturer showing a lower X wind component but stating its demonstrated


perhaps you could give us a bit more detail. The statement probably only makes sense if you are comparing an old Australian AFM (with an increased limit value) with the original OEM POH data ?

[Old Smokey]

Predictably, john_tullamarine has sharpened the pencil. His question later in his reply regarding the age of the Pilot's Operating Manual Vs the AFM is very valid. If, at an early stage, the test pilot could only find, for example, 20 knots, then that is the limit and goes into the POH. At a later time if, say, 25 knots is found and is proven to be safe and controllable, the POH will be revised to reflect this.

On ya JT

Old Smokey

[john_tullamarine]

.. one qualification to Old Smokey's (we must have a beer at some stage .. I would be very surprised if we haven't known each other in previous lives ..) comments ..

Australia no longer views POH demonstrated values as limits, unless the value is qualified to indicate that it is a limit. Provided that a test program is done in the same way as would apply for the NAA of origin, there is no reason why a demonstrated crosswind POH reference cannot be increased for local operations in Australia. If the test crew assesses the handling as being a bit limiting, then one would expect to see a suitable qualification in the POH amendment.

Both in Oz and the US, the operating regulatory provisions covering reckless/dangerous piloting provide a constraint on ad hoc pilot extension of the demonstrated values ...

One should consider that, for most operations, a POH crosswind value of, say, 20 kt is not going to be operationally constraining .. and, for most pilots, the problems associated with limiting crosswind operations are never experienced .. and it can be interesting for the stick and rudder side of things when one has full rudder on during the final approach.

[Mainframe]

john_tullamarine is right on the money with AFM references.

In the General Aviation world, where a crosswind is considered limiting,
it will be included in the "LIMITATIONS" section of the Aircraft Flight Manual (AFM). Usually Sect 2.

These limits may either be handling considerations or structural limitations.

Good examples come to mind, an Auster J5 had, from memory,
a 10kt xwind LIMIT, it was both structural and a handling consideration.
If you've flown one, you would be indeed brave to venture near the limit unless you like excitement.

Another example of structural limitation is the Piper PA34 Seneca, 12 kts Max Xwind,
any more and you may bend the spar and crease the wing skin as outward proof.

If it's not in the limitations section of the AFM, the manufacturer does not consider it limiting.

As JT has already explained, DEMONSTRATED crosswind is just that, on the day of certification,
it was what the pilot and aircraft demonstrated with the available wind on the day of certification,
and does not imply a limitation.

The Cessna 402C, for example has a "maximum demonstrated xwind velocity of 15kts".
This value is listed in the "Normal Operations" section of the AFM under the heading, "Airspeeds for safe operation".

The Aero Commander 500S (Shrike) has a demonstrated xwind of 25kts.

In the practical sense, if you need to operate beyond the DEMONSTRATED xwind values, you have become a test pilot,
and the insurance company may take an interest in what it was that you were attempting.

From an operational point of view, flight planning an aircraft such as the PA34 with an actual published LIMIT
requires that the forecast crosswind be taken into account at the destination for the determination of the need for an alternate.

That operational "REQUIREMENT" does not apply to a "demonstrated" value,
however the prudent pilot would need to evaluate his personal limits and the owner / operator imposed limits.

So we get down to what you can do legally vs what you should do prudently.

A "LIMIT" has the weight of law, a "demonstrated" suggests you have a good think about what you might be tempted to try.

[Mainframe]

Wotsyors

Sorry to offend, but the thread was about definitions.

I do not and did not advocate stepping outside the limits, be they demonstrated or actual limits.

What I very definitely cautioned was that venturing outside ANY published values puts one in the realm of test pilots
and the focussed attention of insurers.

I also mentioned the "PRUDENT pilot" at least twice to clarify. Sorry you did not pick up on that.

The flight planning operational requirement applies to a limit.

Genghis also clarified the definitions, the purpose of the thread.

For a GA aircraft, demonstrated is what was available on the day of certification, nothing more.

For transport category aircraft, demonstrated is most likely not appropriate, a limiting value is sought,
and this means that if what's available on the day is a bit soft,
then the certification may take many attempts over many days to obtain the parameters and boundaries sought.

Hence the Greenland and Sweden trips, also the B777 hot trials in the Australian desert.

Again, sorry if somehow I offended, it was not my intent.

[bookworm]

Mainframe, if , god forbid, you ever have cause to walk back to the pits with your half steering wheel in your hand please, please don`t say " it was only demonstrated and as such is not limiting" this is truly scarey, by the time the lawyers have finished you`ll be in your knickers my friend

Mainframe's reply was too defensive. wotsyors's assertion is simply incorrect. The manufacturer is required to demonstrate satisfactory operation in a crosswind exceeding a particular value and record the "maximum demonstrated crosswind velocity" in the POH. The manufacturer is not required to, and in most cases does not, establish a limitation.

Here are the first three occurences of "maximum demonstrated crosswind velocity" that came from Google, my bold:

From the C172RG POH:
"Demonstrated Crosswind Velocity is the velocity of the crosswind component for which adequate control of the airplane during takeoff and landing was actually demonstrated during certification tests. The value shown is not considered to be limiting."

From a report in Plane and Pilot Magazine:
"The manufacturer provided a “Wind Components” Chart for the Cessna T-R182. The chart had a note reading, “Maximum demonstrated crosswind velocity of 18 knots (this is not a limitation).” "

From NTSB report NYC99LA083:
"The maximum demonstrated crosswind velocity, which was not a limitation, was 11 miles per hour."

How much evidence do you want that the maximum demonstrated crosswind velocity should not be considered as a limitation, by lawyers or anyone else?

[john_tullamarine]

wotsyors.

Long time ago but, as best I can recall, we were getting to the point where we were running out of rudder .. not pleasant at all.

I didn't find that aircraft at all nice in crosswinds.

[batty]

Only a fool will knowingly go outside the demonstrated limits of the aircraft, unless your a test pilot doing trials. It demonstrates poor airmanship and confidence that has not been backed up with adiquate experience.

[Genghis the Engineer]

Only a fool will knowingly go outside the demonstrated limits of the aircraft, unless your a test pilot doing trials. It demonstrates poor airmanship and confidence that has not been backed up with adiquate experience.
Arguably true, but simplistic.

The test pilot, at the end of that certification programme maybe had a few hundred hours on the aircraft. There will later be pilots who have flown many thousands of hours on type, and developed a far greater familiarity with it than the company TPs, however good they were.

So long as no structural limits are exceeded - which is unlikely unless the crosswind landing was mishandled, there may well be cases where a line pilot will be able to safely go beyond the "max demonstrated".

G

[bookworm]

what "particular" value does a manufacturer need to exceed ?

Under US certification rules:

14CFR 23.233 (Normal category)
(a) A 90 degree cross-component of wind velocity, demonstrated to be safe for taxiing, takeoff, and landing must be established and must be not less than 0.2 Vs0.

14CFR 25.237 (Transport Category)
(a) For landplanes and amphibians, a 90-degree cross component of wind velocity, demonstrated to be safe for takeoff and landing, must be established for dry runways and must be at least 20 knots or 0.2 Vsr0, whichever is greater, except that it need not exceed 25 knots.

Strangely, 23.1585(2) requires the "maximum demonstrated values of crosswind for takeoff and landing" to be recorded in the flight manual. I cannot find a corresponding entry for transport category aircraft.

Some manufacturers (Mooney, for example) choose to record exactly 0.2 Vs0 and accompany the AFM entry with an annotation that makes perfectly clear that the value is not to be considered limiting.

(and I'm sorry if my previous post was somewhat sharper than necessary)

[bookworm]

Being a bit thick, but not intentionally, how does this relate to " cross wind limits and definitions ?"

When the words, maximum demonstrated crosswind velocityappear in the Flight Manual, they are there to satisfy the certification requirements I quoted. They are not intended to be limits.

Is there a legal limitation or not ?

If a limit appears in the Limitations section of the Flight Manual, yes. If none does, no. I cannot speak for all aircraft, but I can say that I've seen plenty of Flight Manuals where no limitation exists. Ops Manual limitations may also exist, company by company.

And thanks, wotsyors, as always I'll do a full risk assessment before showering... ;)