Wind Check on final

[ricfly744]

Hello all,

Let's say your MAX TAIL WIND LIMIT IS 15Kts. (B777), at 500ft, you request wind check and tower reports 14Kts, you can officially land, as the only official wind is the tower reported wind.
But, your FMC PROGRESS 2/4, reads a tail wind above 15Kts, you continue, and land. This time, you have been unlucky and skidded off the RWY.
How would you be judged by your company?

The bellow was extracted from an overrun incident investigation:

FDR data was found to indicate that "the average tail wind component during the 15 seconds prior to initial touchdown was 12.95 knots" - in excess of the AFM maximum 10 knot tailwind component for landing. It was noted the same information was available on the MFD, but that Operator SOP for landing and takeoff limitation purposes, was to rely on wind velocity communicated on ATIS or direct from ATC.

The crew followed the SOP but was unfortunate.

Question:1. Does your company recommend or suggests any other wind information for landing that is not the REPORTED TOWER WIND?

2. Do you base your land/go-around decision on the FMC wind information?

Happy flights!

[sabenaboy]

1. no
2. Whenever I'm sure that landing distance will not be a problem, I base my decision on the tower reported wind only.
If there's any doubt, I'll use the highest reading.

[de facto]

Surface winds are picked up about 10 meters above runway...this wind is essential,not winds at 500 ft.
You enter the flare around 30 or 500ft?
Do you look at the FMC at 30'feet?
The tower reported winds would be used in a court of law id think.
If you land with only a few knots to spare,id suggest to reconsider.

Since when winds at heights above your flare height have anything to do with your landing distance?
If atc is untrustworthy,PM at flare initition (50'feet for general landing calculations)may call out TW component.

[RAT 5]

I would suggest that a 12.95kts tailwind, instead of 10kts, was not the cause of an overrun. I suspect there were other parameters at work.
Most AFM's have -10kts as standard, but airlines can research individual runways and apply -15kts. So 3 kts does not cause an overrun.
Every airline I've flown for uses ATC wind. However, it was not uncommon, years passed, for certain Spanish airfields to apply 'calm' when the convenient duty runway was decided. It was calm on landing but -7kts on takeoff.

Continuing, a little in the same vane, I ask for opinions. There are calculations for the adjustment of Vfly for headwind and gusts. There are calculations for the crosswinds including gusts to be compared to the legal limits. There are legal tailwind limits, but I've never read a calculation to include gusts for tailwinds. This aspect has safety implications for over runs. I diverted once for what I considered tailwind gusts to be outside limits. Afterwards I asked for guidance on the tailwind/gust limits. No reply, ever. The performance dept for RTOW's use 150% for takeoff. I asked what about landing? No reply, ever.
I find it strange that at a flight phase where legal limits are in force, and a phase which cause the most accidents, there is no clear answer.
Opinions?

[Good Business Sense]

Unfortunately, despite what many companies write in their manuals and what you all expect they will hang you on your EFIS wind

Warsaw - Luftansa A320 Accident

[/URL] [URL="http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/ComAndRep/Warsaw/warsaw-report.html"]

The crew did not turn to account the wind display on EFIS and did not consider the discrepancy between these data and the information on the wind given by air traffic services. They neither did take into account that tailwind component displayed on EFIS exceeds the value defined by OAM as acceptable for this aircraft.

There is a fantastic book which would shock many called "Air Law for Commanders and their Crews" - it's based on case law i.e. what will apply in court if you have an accident - unfortunately, long out of print.

[FlyingStone]

There are plenty of places in this world where they prolong the obviously required runway change until it's too late and then they force the aircraft already on final approach to continue with landing by advising exactly 10 kts tailwind, despite it's more like 15 or more when you cross the threshold.

From what I know, only the ATC reported wind is valid. Of course, it's good airmanship to briefly look at the wind indication on ND close to ground (but not at 500ft of course) - and to act respectively if major discrepancy is noticed.

FDR data was found to indicate that "the average tail wind component during the 15 seconds prior to initial touchdown was 12.95 knots"

Unless you floated during the last 15 seconds before touchdown, there is no way a normal FDM program would even mention this unless tailwind component below 50ft would be significantly higher than AFM limit. The AFM limitations are for landing, which in this case would count from screen height to touchdown - and that doesn't take 15 seconds.

[ricfly744]

As some of you correctly mentioned, in the overrun incident I used as example, wind was just a factor, but not the cause of the overrun. There was a chain of events. But it was the initial trigger and the crew could have decided not to land.
I mentioned 500 ft for wind check, but could be any altitude. About looking down at progress 2/4 near flare, I agree it's not where our eyes should be, but once you figured the component/ direction from progress, you can refer to the wind displayed at your ND, that is in your normal scan area.
The fact is, we are not told exactly what to do, or what information to use, and when having to decide for a landing or go-around you will end up deciding based on many factors, not only tower reported wind, but most importantly, how comfortable you feel. If you are comfortable, use lower number and land, if not, use the higher and fly away. In case nothing goes wrong, as in most times, you keep your job in either case, but if you get unlucky, then every small detail counts, and it may be against you.

[Capt Fathom]

Is the FMC wind an instantaneous calculation? Or is there a slight delay?

Doesn't make much difference in cruise, but on approach it may be showing what the wind was.

[ricfly744]

I am not sure about any delay, could not find the information in the books.
What is in the book, and many pilots overlook, is that the wind information in progress 2/4 (B777) is in reference to the airplane heading and not track, or runway. This is relevant as you may be crabbing into the wind. So when you de-crab, your crosswind component will increase. Ok, but who will look at that when de-crabbing......impossible in practice....good to know, but in practical terms, irrelevant!

Crosswind (X/WIND)
Displays left (L) or right (R) crosswind component relative to airplane heading.

[AerocatS2A]

The ATC wind is taken from a device that directly measures the wind velocity and designed specifically for that purpose. The FMC wind comes from a calculation involving ground speed, heading, track, and true air speed and is not a direct measurement of the wind. Further, two FMCs in the same aircraft may differ by a few knots in calculated wind. Given the above, I would take the reported wind as gospel and the FMC wind as of academic interest only provided it is relatively close to the reported wind. Additionally the flight manual for the type I'm familiar with states that winds are factored such that a tail wind accounts for not less than 150% of the tail wind, head wind accounts for not more than 50% of the head wind and "reported winds may therefore be used directly".

[PPRuNe Towers]

Processing occurs at both ends of the chain - FMC and Tower,

Mathematical algorithm called a Kalman filter is used and takes several seconds to produce the 'live' readout. A simplified definition of the algorithm would be the combination of information in the presence of uncertainty. It's particularly effective in resolving vector calculations but can take 7 or 8 seconds to produce the result.

You've probably been asked at some point for a 'spot wind' by ATC and the same request from your end can often produce an straight readout without any of the data massaging and inherent delays caused by the kalman filtering.

Rob

[Piltdown Man]

1. We use the reported wind from the tower. Then, if we consider that we can land safely, we do so.

2. No. That would be very unwise. The data is too untrustworthy to use. It also wasn't designed to be used for this purpose.

But isn't that report interesting. I'm surprised that it did not recommend taking the crew out and shooting them to prevent reoccurence. It's just a shame they didn't cover their own arses by telling us what the sampling rates and margins for error were in the FMS computed values. They also might have been generous and given us the effect of the unreported water patches. Nor did they tell you the effect of passing values in kph to crews used to operating in knots. etc...

And no, I'm not worried about losing my job. That is the action taken by naive, small minded, feeble, ineffectual managers who believe that removing rotten apples will sort problems like this out once and for all. My company are above that.

PM

[Derfred]

It is cultural, but not written SOP, in my airline for the PM to read out wind components from the FMC - when relevant, or when requested by the PF.

Examples of when relevant could be:

- near performance limits
- near airframe limits
- changing rapidly
- expected to change rapidly

Is there a scripted mandatory go-around based on FMC wind only? No.

However, if I bent an aircraft and the FMC wind was outside limits approaching the flare, I would be seeking a good lawyer.

[underfire]

Interesting topic.

As noted by others, Winds from the tower are based on a 10m height above the ground, at one location at the airport. The AWOS winds are based on a 2 minute average, including gusts on a 10 minute average.
ATIS winds are updated every 10 minutes, using the same equipment, this is why one must use the tower reported winds for landing.
FMS winds are calculated using the pitot tubes (at least one set front/back) and the distance the INS says it has travelled. Winds are only 2d horizontal headwind and tailwind, as the system can only measure winds in the direction of travel. Depending on the system, the winds are updated every 4 to 5 seconds. Due to latency, it tells you the winds where you were...

When an aircraft is descending, the measurement being only 2D horizontal headwind or tailwind, doesnt really accurately represent the wind because of the 3D vertical component of descent.
Other issues such as turns, once again, winds may not be accurately represented.

Many FMS use a 'blended' wind calculation. The FMS allows for wind input, but only at 3 or 4 locations. There were the forecasted winds in the system from flight ops at departure, the real time winds, and the input winds. Some systems will only update if the winds are outside parameters set from the forecast.
Winds input will be updated on the specific location or waypoint only, but may be blended as an average.

Many of these issues are coming up as a result of the trajectory and time based flow management programs being researched.

Is there a scripted mandatory go-around based on FMC wind only? No.

I wonder about this. Airbus has the automated wind shear alert system, that senses winds, looking for the probability of wind shear. From what I understand, if this system alerts, it is a mandatory GA. I am not certain of the parameters, but from what I understood, it does look at headwind/tailwind, and horizontal/vertical displacement.
Perhaps A drivers can add something about this.

There are also systems that send an ACARS message with data like this for flightdeck use...


Does anyone use this type of information?

[FullWings]

It is cultural, but not written SOP, in my airline for the PM to read out wind components from the FMC - when relevant, or when requested by the PF.

Same here. I think you’d be foolish not to take them into consideration.

Would I initiate a go-around based solely on FMS data? Yes, especially on a tighter/contaminated runway. A GA is generally a non-jeopardy manoeuvre - the same can’t be said of ending up on the stopway or grass, or setting the brakes alight.

I threw an approach away at 50’ in the Caribbean some time ago as it just didn’t seem right with a “calm” wind reported. FDR later showed 23kts tail!

[lederhosen]

This is an interesting question. I would add a couple more issues. My company has excessive tailwind on touchdown as a Foqua item. If you bust it by enough you will get a polite enquiry from our safety pilot, who by the way is a good guy. But you still need to explain yourself.

It is tricky providing evidence that the tower gave you a different wind then the one the plane recorded on landing. You can ask for the tapes but unless you crashed (in which case you have bigger problems) good luck getting these from some military tower in southern somewhere.

Also the issue of gusts and wind varying complicates matters. In theory the gusts may not be limiting. In practice a ten knot crosswind with twenty knot gusts that at the the moment of touchdown are mainly tailwind can be difficult to spot.

The simple rule if in doubt is to go around. The example from Full Wings demonstrates why this is a good idea. We do not have to explain ourselves if we go around, but we do if we bust a tailwind limit, which I think is the right way around.

[Chesty Morgan]

If it's close to your limits just don't ask

[RAT 5]

I threw an approach away at 50’ in the Caribbean some time ago as it just didn’t seem right with a “calm” wind reported. FDR later showed 23kts tail!

Excellent that some of us still have feel and the nouce to act on it; and the courage. I hope RHS learnt a very salient lesson.

However, to those who advocate a GA as first choice: there are many these days flying around on minimum fuel. So you make an unexpected GA. Then what if you are now at RESV fuel? Try again, wait a while or bgr off to said ALTN. CP might not be easily convinced. Surely the length of LDA has to be a major factor and should have been considered in advance. I don't mean that you expected a major wind shift, just that the crew is aware of the LDA & LDR ratio should anything happen.

[lederhosen]

All good advice and clearly you way up all the factors. A recent example I had was the tower giving wind just in limits, shortish runway, checked distance required was ok and then experienced increasing tailwind to nearly double what the tower was saying at 50 feet. Maybe it changed at the last minute, maybe they just wanted to delay changing the runway. It does not really matter. It was obviously way out of limits and with no obvious good reason to push our luck I carried out a missed approach. There is no one size fits all, you exercise your best judgement.

[Jwscud]

Although the tower reported wind is controlling, as mentioned above, there are plenty of places where one should be suspicious of tower reported wind. If the answer to a request for a wind check is "what do you need?" One should be very suspicious of reported winds.

Several airfields in Italy and Spain are notorious for this sort of creative wind reporting. The decision for runway to request is a matter of airmanship. If it's a one way place like Parma, Lamezia, Pescara &c it is wise to have briefed the circling approach so you have it if required. Especially in places where people are being pushy trying to get expeditious runways, don't budge on the runway you want for landing.