Tail wind limitation

[michelda]

Airbus aa/mm have (most of them) 10kt take off tail wind limitation.
Fcom is not speaking of gusting for tail wind limit.
Actual situation, 7 gust 12kt tailwind.
Are we allowed to take off?

thanks for the reply

[B2N2]

Boeing pilot here but our manuals say “steady state” so in your example yes with the understanding that there are no other factors.

[safetypee]

Without any specific limit or guidance, you would also have to consider engine handling for crosswind-component due to gusts as well as pure tailwinds. Also the accuracy of wind reporting.

AFM performance limits for takeoff may be overriding.

https://mms-safetyfirst.s3.eu-west-3.amazonaws.com/pdf/safety+first/engine-thrust-management-thrust-setting-at-takeoff.pdf

Related

https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/airbus-crosswind-development-and-certification.pdf

https://ad.easa.europa.eu/blob/SIB_201420_Crosswind_Operations.pdf/SIB_2014-20_1

[vilas]

Airbus aa/mm have (most of them) 10kt take off tail wind limitation.
Fcom is not speaking of gusting for tail wind limit.
Actual situation, 7 gust 12kt tailwind.
Are we allowed to take off?

thanks for the reply
Tail wind limit is one thing but why should runway be not changed with gusty tail wind that may cross limits? Unless its unidirectional takeoff RW.

[iggy]

Tail wind limit is one thing but why should runway be not changed with gusty tail wind that may cross limits? Unless its unidirectional takeoff RW.

Where I fly regularly ATC prefers to give a wind check that they know is within the limits for most airlines rather than having to change the approach sequence of all the widebody aircraft morning arrivals, plus all the pushback and taxi clearances already given.

Now, once aligned for take off, or crossing the threshold for landing, you are on your own! :}:}:}

[sonicbum]

Airbus aa/mm have (most of them) 10kt take off tail wind limitation.
Fcom is not speaking of gusting for tail wind limit.
Actual situation, 7 gust 12kt tailwind.
Are we allowed to take off?

thanks for the reply

Ciao,

from a limitations and performance point of view yes; the gust is considered only for crosswind components. For head/tail winds the reported steady wind components is what affects You.
If You are using flysmart, try running some computations with varying tailwind gusts and see the effects. You are legal in you scenario.

[safetypee]

The question is not posed as being 'legal' or not; more about safety, sensible, judgement, interpretation.

It is a good question, one which had been asked about crosswinds previously and addressed in different ways by manufactures - interpretation and use of gusts.

In general, AFM values are hard certification limits (tailwind - performance), whereas FCOM values are advisory (demonstrated crosswind - operations).

[sonicbum]

The question is not posed as being 'legal' or not; more about safety, sensible, judgement, interpretation.

It is a good question, one which had been asked about crosswinds previously and addressed in different ways by manufactures - interpretation and use of gusts.

In general, AFM values are hard certification limits (tailwind - performance), whereas FCOM values are advisory (demonstrated crosswind - operations).

In my understanding The OP asks “are we allowed to takeoff” which is a very specific question pertaining mainly to legality and certification. Then whether this is safe and if it’s a good decision on a specific scenario is another matter, based on many different variables.

[safetypee]

Sonic, there is a growing attitude in the industry that if something is 'legal' then it is safe - not so.

Alternatively, a course of action might not be 'legal', but when the choice and rationale is judged safe by the actor, in the situation, at that time, it is a good basis for 'legal' defence if ever required. ( Deffiniton and circumstance of 'legal' required re AFM, FCOM, and actual operation ).

Thus 7kts tail wind meets the requirement of the AFM performance, the 'gust' might not - hence the question. Without clear guidance about this, then prudence might conclude that an alternative runway (#4 vilas) would be a safer option.

In addition, the reported wind accuracy (gusts) might be more important to engine handling at the start of the takeoff, whereas errors in reported wind and gusts further down the runway or after takeoff could effect performance ( cf Denver 737 overrun accident where wind differences across the airport varied by 20kts ).

With respect to the question; I don't know, but with human traits I would probably takeoff … respecting engine operation, … except on a short runway where both engine handling and wind variability could affect performance.
The changeover point … I don't know, but at least with the op question I can think about it.

[sonicbum]

Sonic, there is a growing attitude in the industry that if something is 'legal' then it is safe - not so.

Alternatively, a course of action might not be 'legal', but when the choice and rationale is judged safe by the actor, in the situation, at that time, it is a good basis for 'legal' defence if ever required. ( Deffiniton and circumstance of 'legal' required re AFM, FCOM, and actual operation ).

Thus 7kts tail wind meets the requirement of the AFM performance, the 'gust' might not - hence the question. Without clear guidance about this, then prudence might conclude that an alternative runway (#4 vilas) would be a safer option.

In addition, the reported wind accuracy (gusts) might be more important to engine handling at the start of the takeoff, whereas errors in reported wind and gusts further down the runway or after takeoff could effect performance ( cf Denver 737 overrun accident where wind differences across the airport varied by 20kts ).

With respect to the question; I don't know, but with human traits I would probably takeoff … respecting engine operation, … except on a short runway where both engine handling and wind variability could affect performance.
The changeover point … I don't know, but at least with the op question I can think about it.

I believe You should read more carefully my last post…

”Then whether this is safe and if it’s a good decision on a specific scenario is another matter, based on many different variables.”

You have cited part of those variables in Your post.

[john_tullamarine]

I must be getting to be an old pharte, I guess.

I am concerned with

(a) not killing myself or those along for the ride with me

(b) having a plausible story for the inquiry if it should turn to custard along the way. Having had the opportunity of observing the legal process, their views of what is reasonable might just not be congruent with mine so a pinch of conservatism always looks to be attractive.

safetypee's professional credentials for this discussion are far more than most appropriate.

As for me, depart in a significantly gusting tailwind ? Engine handling problems, possible pitching moment problems, distance problems, low level wind velocity profile problems ? No thanks, not unless it is a case of in extremis and the bad guys are shooting big projectiles or something of similarly dire eyebrow-raising status. As a mentor many years ago offered when I made some stupid, commercially driven suggestion as a newly-minted F/O ... "not even worth our time thinking about, young John".

[Check Airman]

My company specifically states that the gust is to be taken into account when considering wind limits.