A320 Crosswind Question

[b767300]

To all A320 drivers, I have a question

Why the take off crosswind is 29Kts gust 38Kts, while the landing crosswind is 33Kts gust 38Kts.

Any reason for that?

[bubbers44]

My guess is the 29 knots is a fairly common restriction and has to be demonstrated so they probably found the right day when the crosswind was 29 knots. After takeoff the wind may have increased to a 33 knot crosswind for landing so they could certify the ac as such since they demonstrated it.

[b767300]

so this got nothing to do with VMCG & VMCL?

[Mad (Flt) Scientist]

The only certification requirement for crosswind is the 20% Vs0 requirement in para 237, and it never exceeds 25 knots. So none of those numbers were driven by a (Part 25) requirement.

I'd bet that each of them is simply the best they could demonstrate on the day(s) allocated to chasing winds during the certification programme. The version of the A320 limitations I can easily check indicates that those are "demonstrated" limits, not necessarily limiting for the aircraft (although operators may apply them as limits by choice, of course).

And I can't conceive of any linkage to VMC. Appart from anything else, the idea of doing a VMCG test with a (adverse) 29 knot crosswind makes my toes curl!

[airman13]

jets are for kids....I meant playstations....

[dkz]

very smart answer ... are you for real ? (sour grapes maybe ?):ugh:

[420]

boy i would really like to be the one to answer this cos i cant believe i never actually even thought about the "why" in this. Bravo!:D

hmmm... ok what do u guys think about the fact that perhaps the auto rudder trim function has something to do with this? in the air perhaps with the fact that the rudder will automatically trim for the crosswind to perhaps a certain limit (im guessing 33kts so whatever the aircrafts angle has to be to counteract this and maintain centerline) but on the ground during the take off roll,u dont have this auto rudder trim support and the limit is higher (29kts). but then again... its only 4kts...which makes me doubt my answer as well:ugh:

even if it has something to do with vmcg or vmca which i doubt cos yeah it would make my toes curl as well if they actually tested it that way, it still is ONLY 4KTS!!! why???:confused:

guys...this is one for the french i think:ok:

[Mad (Flt) Scientist]

Stop trying to determine a reason for the numbers; there won't be one, technically. It's just the wind they measured on the day they did the test; it's not LIMITING, just DEMONSTRATED. There was a bit more wind at a different time, so they got a different demonstrated number. Happens all the time.

[fantom]

Mad FS is correct, as always, but the 'demonstrated' bit has caused problems.

I remember pilots (who didn't fancy the weather that night) quoting the FCOM W/Vs as limiting.

As for a VMCG demonstration 29/38, I'll give that a miss, thank you.

[420]

yeah i guess i agree about the fact that its demonstrated only and not limiting. MADFS is right. but we cant work with demonstrated,we need guidelines... but i guess that comes down to judgement in the end.

hahaha fantom... i hear ya. same here. GO-AROUND FLAPS! thank you.:ok:

[john_tullamarine]

but we cant work with demonstrated

why ever not ? However, if an operator/pilot chooses to operate at a higher crosswind, then explaining the action after the incident rests with that operator/pilot .. certainly not the OEM or regulator. The OEM isn't going to waste a bunch of time and money chasing excessively strong crosswinds unless someone (read operator) wants to PAY for the work... and the typical OEM is quite happy to do just that .. but the dollar is ALWAYS high ...

[loc22550]

Indeed MAD is correct..X wind value for landing and take off are not limitation but demonstrated one.
So if tomorrow you manage to land a A-320 with 40kts X-wind:\ just call airbus and tell them to change the value for the max demonstrated x-wind landing in the FCOM3...:)

But For AUTOLAND the value given are well LIMITATION...
Cheers.

[alf5071h]

“ we need guidelines... but i guess that comes down to judgement in the end.”

Some authorities make demonstrated values mandatory, similarly any operator can choose to do this; this action provides hard rules on which to base your judgement.
However, if your operator works with ‘demonstrated’ values, then you might wish to read Safety aspects of aircraft operations in crosswind. (www.nlr-atsi.com/downloads/NLR-TP-2001-217.pdf)
This report discusses how reported winds can vary and thus how your judgment should be moderated: – quotes.
“substantial deviations from the reported wind characteristics can occur”, and
“that a reasonable probability does exist, that while wind reports to the pilot do indicate that crosswind is not exceeding 15 Kt, in reality the actual encountered crosswind … can deviate 10 Kt or even more from the reported wind. For even higher reported crosswinds, deviations may increase accordingly.”

Good judgment depends on awareness of the situation which in turn requires knowledge, skills to make the assessment and of course discipline both in thought and action, … which approximates to airmanship (after T Kern), and that would also include considering the further limiting effects of a wet or contaminated runway.

Edit: The recent Airbus Briefing Note on Landing Techniques - Crosswind Landings (www.airbus.com/en/corporate/ethics/safety_lib/index.html), references (via a link) a document titled “Understanding Forecast / ATC / Aircraft Wind Information”. The link is not active; has anyone a copy of this document or is it to be a future BN from Airbus?
See also para VI Understanding Crosswind Landing Limitations

[Mad (Flt) Scientist]

but we cant work with demonstrated
Demonstration is somewhat the aviation equivalent of the old cartographers' "Here Be Dragons". We don't know what happens above that value, so we can't say it's horrible, but we (as OEMs) sure aren't going to encourage people to go be test pilots with 100 souls sat in blissful ignorance behind them. So we warn you where we've been, and rather let you draw your own conclusions as to the wisdom of experimentation.

[john_tullamarine]

....and rather let you draw your own conclusions as to the wisdom of experimentation ...

and then, after the rending of metal (and carbon fibre) bits and pieces ... be prepared to defend the decision to undertake that experimentation in court or the BOI or the Royal Commission or whatever form of enquiry your jurisdiction adopts ...

Having been exposed to some crosswind testing I suggest that one needs to be aware that it is not just a matter of suck it and see .. one can get into a few sticky situations as the wind increases. I recall one light single which came out with a modest demonstrated value (15kts or so) .. being commercially driven, the local distributor wanted a more useful value. A TP mate and I, all approved and so forth, went forth and frightened ourselves with a resulting limit of, as I recall, 18kts .. it all started to go a bit pear shaped much above that figure ...

And it would be crass to relate tales of SuperCubs, strong crosswinds, glider towing .. and then trying to get back on the ground without destroying too many gable markers .. they do explode with a most satisfying and resounding "bang" .. thankfully I am now a lot older, far less interested in excitement .. and more than happy to contain myself within 30 kts for fun ...

[non iron]

When the tripple seven was being trialled Greenland wasn`t cold enough. They hopped over to Luleo to catch the cold spell l believe.
Minus 35 as a minimum, with doors etc left open over night.
Demonstrated.
In the same neck of the woods Skyways Sf340`s were grounded if the temp dropped below -35c. ln Kiruna that was the main cause of winter `no goes`.
The envelope starts at -35c and since that is what has been demonstrated then that is the limit. ( mitigated by being towed on arrival inside a warm hanger for the pax to disembark ).

Anyway, cross wind limits are demonstrated also and to think that a ten knot difference between t/o and ldg is in anyway structurally limiting is fanciful.

John, forgive me if l`m wrong but l don`t think so. Pete.

[FliegerTiger]

Nothing to do with Vmcg as this doesn't allow for crosswind.

[john_tullamarine]

.. but he who doesn't consider the effect of crosswind for a min speed schedule takeoff trusts in the little faeries down at the end of the garden path, methinks ...

The significance of the nil wind is solely line in the sand stuff .. for the very great majority of circumstances, it is not at all critical or even significant .. but beware of strong crosswinds and low weight min speed schedules .. the "real" Vmcg can be a significant number of knots above the certification animal.