Crosswind limitations

[flyinGuppy]

I've searched the forum on this topic but I still have some questions about it.

For example lets take the B737 for witch a read in other topics the crosswind limit is around 35 kts.

That limit is valid for example if the metar shows something like 29010G35kt 250V340?

I mean, you can land if the crosswind component is up to 35 kts, but is that valid if the mean wind has a huge difference from the gust, or if the wind isn't blowing steady from one direction?

If not, how many degrees can the wind be shifting its direction before the limit has to be lowered, or how many knots must the mean value of the wind differ from its gust for that matter?

Tanks for your attention

RM

[behind_the_second_midland]

You work out the x-wind component of the reported wind either by hand or put the wind in the FMC.

If that is in then you land if not go around.

Its sometimes "handy" to ask for no more wind checks at,say,200 feet if the last one was in:ok:

In BA, for planning purposes, gusts need not be taken into condiseration except for ETOPS flights at the planning stage.

[mark twain]

As an instructor we teach students to consider the difference between the wind angle and runway orientation.

Therefore with a runway 27 (270 degrees) a wind of 270 is a total headwind. A wind of 360 is total crosswind.

In practise you teach the students to calculate the difference and work on the following basis:

Basically a difference is directions calculated - so runway 27 (270 degrees), wind 300/20 - the difference is 30 degrees.

Simply you can assess the approximate crosswind as follows:

Difference 0-15 degrees - nothing to a quarter of the wind - so 20 knot wind the crosswind is a maximum of 5 knots.

15-30 degrees - a quarter to half the wind - so using the 20 knot wind the crosswind would be a maximum of 10 knots.

30-45 degrees - half to three quarters - so again using 20 knots the maximum crosswind you should expect is 15 knots.

Between 45-60 - three quarters to full crosswind, as you hit 60 degrees off we tend to tell students to consider it all crosswind.

If gusts are forecast or declared then we use half the 'gust factor'. So 20G30 we take as a 25 knot wind, ie 20 knots base plus half the gust of 10 knots.

Typically with light aircraft we have limits between 12-20 knots, but then again we often have more runway options than the big guys!

Hope that helps.

Mark

[BOAC]

I have to differ from B-T-S-M, in as much although BA SAID do not 'consider' the gusts, I always did - 'consider' when flying for BA! - 'twas my right :D

Never expect me to land in 90 off at 30 gusting 60 - unless there was NOWHERE else to go, of course!

BTW, flyin, I THINK the max demonstrated 737 xwind was 40kts.

[flyinGuppy]

Tank you for your replies, but that's not exactly what I wanted to know.

Let me try to explain my self better.

What I was trying to learn is when will you say it's a no go, even if the winds are within the maximum limitations of the aeroplane you are flying, being the reason for the no go, a strong wind variation or strong gusts, many knots above the mean wind.

I ask this because in Azores we have some airports that lay near mountainous terrain, well there wasn't any place better where to put them, and because of that fact the wind can be a little "wild". Some times we have metar's showing something like VRB20Kts, or 27010G35kts 230V310

What would you do in cases like this? How high can be the spread between the mean wind and the gusts before you decide to divert? I heard that if you have a gust 15kts stronger than the mean wind you should consider diversion, is this true?
How big can be the direction change, I mean If you have a runway 18/36 and the wind is form 27020Kts 200V340 you have the wind changing from almost a headwind to almost a tailwind in both runways! What would you do? Do you just consider the most limiting wind that variation can produce and use the normal limits, or do you have some other ways to deal with it?

If you encounter such changing winds in finals wont the aircraft start screaming WINDSHEAR WINDSHEAR and if so don't you have to abort?
So how do things work when the winds are not stable?

Tanks again for your attention, and please forgive my English.

RM

[BOAC]

I ask this because in Azores we have some airports that lay near mountainous terrain, well there wasn't any place better where to put them, and because of that fact the wind can be a little "wild". Some times we have metar's showing something like VRB20Kts, or 27010G35kts 230V310

What would you do in cases like this? How high can be the spread between the mean wind and the gusts before you decide to divert? I heard that if you have a gust 15kts stronger than the mean wind you should consider diversion, is this true?

******Not in my experience. It is down to:
experience
reports from other a/c
how big the gusts are and how much they swing

remember also there is max actual windspeed for most aircraft, above which taxying is difficult and a structural check may be required

Corrections are made to approach speed to cope*******

How big can be the direction change, I mean If you have a runway 18/36 and the wind is form 27020Kts 200V340 you have the wind changing from almost a headwind to almost a tailwind in both runways! What would you do? Do you just consider the most limiting wind that variation can produce and use the normal limits, or do you have some other ways to deal with it?

**** The example you give would exceed the maximinum allowable tailwind for most aircraft! So, refer to 1) above**********:D :D

If you encounter such changing winds in finals wont the aircraft start screaming WINDSHEAR WINDSHEAR and if so don't you have to abort?

******probably yes, and best not to have commenced the approach in the first place! There are situations where a WINDSHEAR warning does not require a g/a*****

[Onan the Clumsy]

even if the winds are within the maximum limitations of the aeroplane you are flying Correct me if I'm wrong, but (in light a/c at least) this isn't a limit so much as a maximum demonstrated value. Not that it wouldn't be sensible to treat it as a limit, but, unlike Vne for instance, it's not an actual, fixed, legal, engineering based, designed etc limit.


Also (again with light a/c) you may have the option of landing diagonally across the runway to lessen the x-wind component.

(unless of course, it's a componant :8 )



your english is very good btw.

[-IBLB-]

Correct me if I'm wrong, but (in light a/c at least) this isn't a limit so much as a maximum demonstrated value. Not that it wouldn't be sensible to treat it as a limit, but, unlike Vne for instance, it's not an actual, fixed, legal, engineering based, designed etc limit.

This is correct, and you could go over this crosswind limitation, and still be legal. But i wouldn't do this unless you have no other option, usually ( i know, there are exceptions to everything ) it is advisable to find another runway.

On some aiplanes, there is a "hard" limit.
This is usually to do with either the rudder-ability to control the a/c, or in case of the 737, max bank angle close to the ground because of the possibility of a pod-strike.

As said by BOAC usually you would consider the most limiting situation, and decide from there, with the plane and company procedures, and you personal limitations in mind, what the best plan of action is.

I would never advise anyone to land diagonally across a runway as said by OtC, because it will hardly make a difference in a situation with a steady crosswind, but also because in a situation with a lot of varying crosswind, it has no effect whatsoever. Just an extra risk if you ask me.

If you are not sure wheter or not you can make it safely in given circumstances, it usually means you should look for something else.


-IBLB-

[alexban]

B737-300 has a demonstrated crosswind for landing at 35 kt.This is not a limitation.
So it depends entirely of your experience.I know a crew that landed a 737 with a steady 59 kt crosswind(with minor gusts).I wouldn't do it myself,except if no other choice.
There are airports,for ex Madeira,where it says clearly if the wind blows from direction x with velocity y then no land.
Otherwise you may try an approach.If at any time it becomes an unstabilized app due to wind for ex,you go around.
If you receive windshear alert..go around.
If you don't feel safe about landing ..tell the cpt ,or if you are the cpt ..go around.
If your SOP has a strict limit specified,I guess you should take the steady wind.If by any chance the app become unstabilized then go around.You should call for a wind check on final stage of the app.

IBLB...the 737 won't strike the rwy with the pod at high bank..even though the pods looked like smashed to the rwy more then once :)
it will be the flaps that touches first,but at high bank angles only.
for ex at a pitch of 5 deg,you'll strike the flap track fairing at a bank of more than 11 deg (assuming using flap 40). You'll strike the nacelle only at pitch less than 0 deg.(for 737-300)
For NG the bank allowed is higher by 3-4 deg.
Brgds...
Alex

[-IBLB-]

i learn something new every day :D

-IBLB-

[Piltdown Man]

How long is a piece of string? If concerned about limits, ask for "instantanious wind checks" on the approach or when cleared for take-off. But I'd suggest that if your limit was 35 knots, you would be "in" on that wind.

The MET section of the Air Pilot tells you how much things have to change to be reported.

[AirRabbit]

I’m surprised to hear that any procedure would call for using “half the gust” when considering wind. Usually the wind additive is “half the wind, all the gust” during final, and planning to bleed off the “wind” factor (retaining the gust portion) between the threshold and touchdown. A good share of the aircraft in operations today have only a “max demonstrated crosswind.” This is almost always because during flight testing they couldn’t find a crosswind any higher. What we need to remember is that the crosswind values (limiting and max demonstrated) are normally measured at a height of 10 meters above the runway – and there are very few wind conditions that are the same at the surface as they are at 33 feet above the surface. Most wind values reported by tower personnel are from an anemometer that is a lot closer to the surface than to 33 feet -- where the wind speed is almost assuredly lower than what you’ll encounter in the flare. And, most critically, just because the airplane has a maximum crosswind limit, that doesn’t necessarily mean that the pilot is going to be able to handle that wind. I believe it is the mark of a true professional to know his/her own limits (including crosswinds) as well as the limits in the manual – and will take considerable care to not exceed those personal limits. A very wise instructor once told me, “the book never landed the airplane.” ;)

AirRabbit

[unfazed]

Airrabbit is right

The aircrfaft has a max demonstrated XW , this is not a limit !

The amount of crosswind that you accept depends on your proficiency, experience level and ability in dealing with the conditions.

Oh and also what you think your company and insurance companies policy will be if you push things too far !(SOP's)

Working from a runway that constantly experienced very strong sea "breezes" at 90 degrees to the only runway if everybody adhered to the "max demonstrated" then you would have a very quiet airport.

[safetypee]

I have been directly involved or associated with several aircraft types in the determination of max demonstrated crosswind. XW landings have to be demonstrated in measured wind conditions from approaches to each end of the runway in the same conditions. The statement required is that the ability to control the aircraft during the landing was not found to be limiting. To some extent most manufacturers take into consideration the ‘average’ pilot, but as we know there are few definitions of the average pilot.

The landings which I conducted were not 'limiting'. However in the particular conditions on the day, the ability to approach and align the aircraft with the runway on finals was at the limits of sensible flight, thus the overall limit in my opinion, but this type of information is rarely published.

There might be an interesting discussion amongst test pilots as to exactly how many XW landing tests have been found to be limiting, and why. Clearly if the aircraft cannot be positioned on finals, or the drift controlled before touchdown, then the ultimate limit has been reached/exceeded. I do not know of any tests that have resulted in the aircraft leaving the runway sideways. Thus, for any published max demonstrated wind the average pilot has little or no knowledge of how far his XW landing will be from the real limit; nor does that pilot know if he/she is above or below average on that day.

I would recommend a personal limit somewhat less than the max demonstrated, and a significantly larger margin for gusting conditions, wet runway, limiting runway length, and those other things that we should consider before landing – what if.

[unfazed]

Safetypee

"Clearly if the aircraft cannot be positioned on finals, or the drift controlled before touchdown, then the ultimate limit has been reached/exceeded. "

Now that is a very definite limit - On the approach if you run out of Rudder authority to maintain centreline and you cannot stop drift then you have no other choice but to find another runway

You will find that this point is reached long after "max demonstrated book values"

[safetypee]

unfazed the point which I might not have made clear, was that in my experience on one aircraft type involving several flights to determine limiting conditions, and in discussion with other pilots who conducted tests on the same and other aircraft, the margin between having problems on the approach and any loss/lack of control on the runway did not appear to be large. You appear to indicate otherwise by suggesting that the control limit on the runway is reached long after having approach problems.

The approach problems that I experienced did not involve rudder, just the inability to maintain a semblance of wings level flight and line up with the runway, but at touchdown and rollout, control was not limiting. In my opinion there was little control margin remaining.
If crews have the type of problems that I encountered on the approach then I think we agree that this is the point at which to fly go around and divert. Are you suggesting that they conduct their own mini test to establish the available rudder control during the flare? I hope not, because as I stated the margin for error between having adequate control for aligning, or being insufficient for a safe landing and rollout is very small.

The difference between a certification limit and a max demonstrated value is that the former has been determined under controlled conditions against a set of requirements, which in general provide additional margin for variation in operating technique, crew ability, and environmental conditions, for the flight conditions based on that limit e.g. V1 and Vmcg, or V2 and Vmca. However, the max demonstrated crosswind value is something that has been achieved without further qualification and generally without indication as to any margin from the ultimate limit.

[unfazed]

No I agree with what you are saying

If you encounter difficulties on the approach (e.g.) during the descent to land then you can guarantee problems during the flare to land (unless there is a very strong wind gradient with calmer conditions at the surface)

My point is really that from experience the max demonstrated listed in the aircraft operating manual appears to indicate what the max wind was that was flown during testing, it is a reasonable gudeline as to what may be "sensible" but would appear to satisfy insurance companies and those still training more than competent and experienced pilots.