Wind Check on final
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FMS wind
The FMS wind is computed as a vectorial difference between the airspeed aligned to the aircraft heading and the ground speed aligned to the ground track. The FMS-calculated wind vector is normally displayed on the Navigation Display (ND) or on the Control Display Unit (CDU). Some FMS installations provide a decomposition of the wind vector in cross- and tailwind components. The FMS calculates the wind for the altitude the aircraft is actually flying. Note that tailwind limits and the tailwind used for field performance refer to the wind measured at a 10-meter height. The FMS wind is therefore of little value to the pilot when he makes his decision to land, i.e. at top of descent, during descent and upon initiation of the final approach. Nevertheless many pilots tend to monitor the FMS for exceedance of the maximum tailwind.
Uncertainties exist in the determination of derived inertial quantities (like ground speed and ground track) that will influence the accurate determination of the FMS wind vector. Especially the calculation of the drift angle should be treated with suspect in a dynamic environment like an approach. Secondly, the airspeed is assumed to be aligned with the heading, sideslip is not measured nor incorporated in the calculation of the FMS wind, yielding questionable results once the aircraft has commenced decrabbing in crosswind conditions that might be present as well. Finally, FMS computations are filtered, resulting in a typical time delay of 3-5 seconds. A second relevant effect of this filtering process is that gust values will not be displayed to the flight crew. For these reasons the use of FMS wind is normally accurate only in the cruise phase of the flight. However, it can be shown that, although the crosswind component determined by the FMS can be highly inaccurate in the final phase of the flight, the tailwind component is relatively insensitive to FMS errors in the determination of the drift angle. This is a direct result of the geometry of the speed vectors involved.
The FMS wind is computed as a vectorial difference between the airspeed aligned to the aircraft heading and the ground speed aligned to the ground track. The FMS-calculated wind vector is normally displayed on the Navigation Display (ND) or on the Control Display Unit (CDU). Some FMS installations provide a decomposition of the wind vector in cross- and tailwind components. The FMS calculates the wind for the altitude the aircraft is actually flying. Note that tailwind limits and the tailwind used for field performance refer to the wind measured at a 10-meter height. The FMS wind is therefore of little value to the pilot when he makes his decision to land, i.e. at top of descent, during descent and upon initiation of the final approach. Nevertheless many pilots tend to monitor the FMS for exceedance of the maximum tailwind.
Uncertainties exist in the determination of derived inertial quantities (like ground speed and ground track) that will influence the accurate determination of the FMS wind vector. Especially the calculation of the drift angle should be treated with suspect in a dynamic environment like an approach. Secondly, the airspeed is assumed to be aligned with the heading, sideslip is not measured nor incorporated in the calculation of the FMS wind, yielding questionable results once the aircraft has commenced decrabbing in crosswind conditions that might be present as well. Finally, FMS computations are filtered, resulting in a typical time delay of 3-5 seconds. A second relevant effect of this filtering process is that gust values will not be displayed to the flight crew. For these reasons the use of FMS wind is normally accurate only in the cruise phase of the flight. However, it can be shown that, although the crosswind component determined by the FMS can be highly inaccurate in the final phase of the flight, the tailwind component is relatively insensitive to FMS errors in the determination of the drift angle. This is a direct result of the geometry of the speed vectors involved.
The FMS wind is therefore of little value to the pilot when he makes his decision to land at top of descent, during descent and upon initiation of the final approach
If the FMS is showing a 15kt tailwind at 200ft, then you'd better have a good look at the windsock before you flare.
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This job has and will always have a requirement for common sense and self preservation.
As a Captain you should take all information into account. That's CRM.
So to suggest that ATC is more or less important than the FMS is totally missing the point. There all relevant to getting the job done. To also suggest TRE/management should be able to give a clear answer to every possible scenario is not realistic.
I have had exactly this scenario on the 777. ATC reporting 12 kt tailwind (limit 15kt) and FMS 16kt tail all the way down the approach. My decision was at minimum if FMS still showing more than 15 we go-around simple. It went to 13 and we landed. I don't need to ask management because management have appointed me to make the decision.
At that moment its my aeroplane, my career and my life. If asked as an instructor I can give this as an "opinion/technique" not company policy. Its not written down and never will be. Its called getting the job done.
If ATC states something is within limits but you have another source of information to the contrary surely you take the sensible safe decision and use that information !
RAT 5....I have never heard of an "unexpected Go-around". Shouldn't every approach be a fully planned Go-around and the landing is the bonus. Its interesting to see guys pre-selecting ground frequency when handed over to tower. You know a Go-around has gone from the mind
As a Captain you should take all information into account. That's CRM.
So to suggest that ATC is more or less important than the FMS is totally missing the point. There all relevant to getting the job done. To also suggest TRE/management should be able to give a clear answer to every possible scenario is not realistic.
I have had exactly this scenario on the 777. ATC reporting 12 kt tailwind (limit 15kt) and FMS 16kt tail all the way down the approach. My decision was at minimum if FMS still showing more than 15 we go-around simple. It went to 13 and we landed. I don't need to ask management because management have appointed me to make the decision.
At that moment its my aeroplane, my career and my life. If asked as an instructor I can give this as an "opinion/technique" not company policy. Its not written down and never will be. Its called getting the job done.
If ATC states something is within limits but you have another source of information to the contrary surely you take the sensible safe decision and use that information !
RAT 5....I have never heard of an "unexpected Go-around". Shouldn't every approach be a fully planned Go-around and the landing is the bonus. Its interesting to see guys pre-selecting ground frequency when handed over to tower. You know a Go-around has gone from the mind
Last edited by 8che; 15th Oct 2015 at 07:41.
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RAT 5....I have never heard of an "unexpected Go-around". Shouldn't every approach be a fully planned Go-around and the landing is the bonus. Its interesting to see guys pre-selecting ground frequency when handed over to tower. You know a Go-around has gone from the mind
8che: Totally agree. I must have been unclear about my true meaning. I've spent years drumming into students that every takeoff is an RTO and every approach is a G/A. Only when past the PNR for either phase is it your lucky day. Your last comment about freq' use always gave me the eebyjeebies and was a no no. Usually the trick of smart asses, or so they thought.
We are in violent agreement.
8che: Totally agree. I must have been unclear about my true meaning. I've spent years drumming into students that every takeoff is an RTO and every approach is a G/A. Only when past the PNR for either phase is it your lucky day. Your last comment about freq' use always gave me the eebyjeebies and was a no no. Usually the trick of smart asses, or so they thought.
We are in violent agreement.
Last edited by RAT 5; 15th Oct 2015 at 16:00.
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8che;I don't need to ask management because management have appointed me to make the decision.
At that moment its my aeroplane, my career and my life. If asked as an instructor I can give this as an "opinion/technique" not company policy. Its not written down and never will be. Its called getting the job done.
Exactly, very well said and a perfect summary of what captaincy is all about.
At that moment its my aeroplane, my career and my life. If asked as an instructor I can give this as an "opinion/technique" not company policy. Its not written down and never will be. Its called getting the job done.
Exactly, very well said and a perfect summary of what captaincy is all about.
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My decision was at minimum if FMS still showing more than 15 we go-around simple.
If you go around at 200 ft because your FMS shows TW of 16kts,it is your prerogative of course,however i rather rely on tower and if at 50 ft it is still way above then initiate a go around otherwise when all land with threshold TW of 10kts and go home while you will safely go to your alternate.
I agree with all the rest,it is the captain decision.
Should an additional 3kt of tailwind alone result in an overrun? Hopefully landing performance was calculated with the maximum tailwind of perhaps 10kts. If there was an additional 3kts during the landing, whilst this is outside of the a/c performance limitation, any excess energy would be contained by the performance safety factor wouldn't it?
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Should an additional 3kt of tailwind alone result in an overrun? Hopefully landing performance was calculated with the maximum tailwind of perhaps 10kts. If there was an additional 3kts during the landing, whilst this is outside of the a/c performance limitation, any excess energy would be contained by the performance safety factor wouldn't it?
Just to throw it on he table for a bar-room chat. Purely the over-run question.
A/C has -10kts AFM limit. Company has some airfields with -15kts approval. So a/c is capable of landing in -15kts; aerodynamically.
B737 landing F40 LDR < LDA by a good margin.
SE F15 landing. Vref15 = Vref40 +20.
TE flaps up landing. Vref = Vref40 + 40.
All flaps up landing Vref = Vref40+55.
The LDR is then factored = 1.3. The LDA is long enough for all these scenarios with good BA. Thus the runway is long enough to have a touchdown GS similar to a very strong tailwind.
Can you land F40 A/C in normal condition.
1. practically,
2. safely,
3. legally?
I'm only asking it against the idea that a 3-5 kts extra tailwind requires GA or even diversion. It is the written limitation that casts doubt and that addresses No. 3, but what about No. 1?
Limits can be very limiting. Just a light discussion.
Just to throw it on he table for a bar-room chat. Purely the over-run question.
A/C has -10kts AFM limit. Company has some airfields with -15kts approval. So a/c is capable of landing in -15kts; aerodynamically.
B737 landing F40 LDR < LDA by a good margin.
SE F15 landing. Vref15 = Vref40 +20.
TE flaps up landing. Vref = Vref40 + 40.
All flaps up landing Vref = Vref40+55.
The LDR is then factored = 1.3. The LDA is long enough for all these scenarios with good BA. Thus the runway is long enough to have a touchdown GS similar to a very strong tailwind.
Can you land F40 A/C in normal condition.
1. practically,
2. safely,
3. legally?
I'm only asking it against the idea that a 3-5 kts extra tailwind requires GA or even diversion. It is the written limitation that casts doubt and that addresses No. 3, but what about No. 1?
Limits can be very limiting. Just a light discussion.
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I'm amazed that this is getting so much replies. The topic could have been closed after the first reply ( mine 
)
a) If it's legal for you to land and there's no doubt on your mind that a safe landing can be made, then go ahead and land.
b) If there's any doubt on your mind that a safe landing can be made, whatever the twr reported wind may be, then go-auround and find a better option.
I recently made a go-around in Rhodos Rwy 25 (3305 m length) in an A320 at 58T landing weight, because the twr reported 12 kts tailwind. Landing on R25 would have been safer then what we ended up doing: a go-around and vectors for a VOR app on Rwy 07 with crosswind and moderate turbulence on short final. Was it unsafe to go around? Maybe not. But the go-around and landing on 07 added nothing to safety and it took extra time, extra fuel and it would needlessly scare some passengers. I knew that before I initiated the go around!
I made a go around just because I feared that someone might file a report that I landed with a reported 12 kts tailwind and not because that was the safest thing to do. If you think about it, that's nothing to be proud of! (Sadly some people will say that thinking or using common sense is not done according to SOP)
It's a pity that it has come to the point that sometimes you have to be afraid of choosing the safest and best decision...
(Standing by now to get flamed because I dared to say that landing with 12 kts tailwind under the given circumstances would have been safe. Of course it's perfectly safe to land with 10 kts tailwind, but reckless to land with 12 kts tailwind.
)
)a) If it's legal for you to land and there's no doubt on your mind that a safe landing can be made, then go ahead and land.
b) If there's any doubt on your mind that a safe landing can be made, whatever the twr reported wind may be, then go-auround and find a better option.
I recently made a go-around in Rhodos Rwy 25 (3305 m length) in an A320 at 58T landing weight, because the twr reported 12 kts tailwind. Landing on R25 would have been safer then what we ended up doing: a go-around and vectors for a VOR app on Rwy 07 with crosswind and moderate turbulence on short final. Was it unsafe to go around? Maybe not. But the go-around and landing on 07 added nothing to safety and it took extra time, extra fuel and it would needlessly scare some passengers. I knew that before I initiated the go around!
I made a go around just because I feared that someone might file a report that I landed with a reported 12 kts tailwind and not because that was the safest thing to do. If you think about it, that's nothing to be proud of! (Sadly some people will say that thinking or using common sense is not done according to SOP)
It's a pity that it has come to the point that sometimes you have to be afraid of choosing the safest and best decision...
(Standing by now to get flamed because I dared to say that landing with 12 kts tailwind under the given circumstances would have been safe. Of course it's perfectly safe to land with 10 kts tailwind, but reckless to land with 12 kts tailwind.
)
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Here where I fly, the company uses the CDU'S PROGRESS page as the source data for a Continue/Go Around call at the DA.
Nevertheless I've already seen quite a couple landings with a tail wind slightly above the limit (1, 2kt) and none of us ever got a call from that.
It's interesting, however, that we are not following down here what looks like most of the world's operators do (tower wind) as the official data for backing up the decision process. Probably they just don't trust the ATC, and I can understand that (South America).
Great discussion guys,
All the best.
Nevertheless I've already seen quite a couple landings with a tail wind slightly above the limit (1, 2kt) and none of us ever got a call from that.
It's interesting, however, that we are not following down here what looks like most of the world's operators do (tower wind) as the official data for backing up the decision process. Probably they just don't trust the ATC, and I can understand that (South America).
Great discussion guys,
All the best.
In the UK, reported ATC winds are usually a 2 min average with 'instant' wind available on request. ATIS are usually updated every 30 min and the wind on this and the METAR is a 10 min average at the time of the ob and hence could be up to 20 min out of date.
Some units may not have the facility for a 2 min average report and will say 'instant wind is......'
Some units may not have the facility for a 2 min average report and will say 'instant wind is......'
In isolation, you could probably stop most aircraft quite safely within the LDA with a 30kt tailwind, assuming you landed in the right place at the right speed. You could also take off 10% overweight and would be fine as long as nothing else went wrong. Busting minima on a precision approach will get you in 99.9% of the time.
It’s like Stabilised Approach Criteria. Most operators have a hard limit below which THOU SHALT NOT GO if you do not satisfy your SAC and also instructions to throw the approach away should you deviate from them later on. Much of this came from post-accident analysis where there was found to be a high correlation between unstable approaches and runway excursions. A good way to reduce the incidence of UA to landing? Make it simple to reject an UA and back that up with FOQA. You have to draw a line in the sand somewhere to stop people “having a go” believing they are doing their best for passengers and company.
With tailwinds, there are SOP/FCOM limitations. If you knowingly and deliberately (as judged by your company/authority) operate beyond these, as opposed to “accidentally”
then you are placing yourself in a rather precarious position should anything happen, even if it is not directly related.
In an emergency, of course, I would take a serious out-of-limits tailwind fully expecting to get away with it but why turn a routine flight into an emergency? I’m paid to avoid that.
It’s like Stabilised Approach Criteria. Most operators have a hard limit below which THOU SHALT NOT GO if you do not satisfy your SAC and also instructions to throw the approach away should you deviate from them later on. Much of this came from post-accident analysis where there was found to be a high correlation between unstable approaches and runway excursions. A good way to reduce the incidence of UA to landing? Make it simple to reject an UA and back that up with FOQA. You have to draw a line in the sand somewhere to stop people “having a go” believing they are doing their best for passengers and company.
With tailwinds, there are SOP/FCOM limitations. If you knowingly and deliberately (as judged by your company/authority) operate beyond these, as opposed to “accidentally”
then you are placing yourself in a rather precarious position should anything happen, even if it is not directly related.In an emergency, of course, I would take a serious out-of-limits tailwind fully expecting to get away with it but why turn a routine flight into an emergency? I’m paid to avoid that.
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De facto,
Deciding on a Go-around at 50ft in a B777-3 when you had the choice to do it earlier puts you at very high risk of striking the tail and therefore very poor judgement ! At that height even with a perfectly executed G/A the gear will likely strike the runway leaving as little as 8 degrees pitch to tail strike. You have to be incredibly careful but that comes with knowing your aeroplane. Delaying the decision until 50ft is not on with aircraft of this size. They will punish "push-on-itis" severely. I'll leave that kind of thinking to guys flying puddle jumpers !
Deciding on a Go-around at 50ft in a B777-3 when you had the choice to do it earlier puts you at very high risk of striking the tail and therefore very poor judgement ! At that height even with a perfectly executed G/A the gear will likely strike the runway leaving as little as 8 degrees pitch to tail strike. You have to be incredibly careful but that comes with knowing your aeroplane. Delaying the decision until 50ft is not on with aircraft of this size. They will punish "push-on-itis" severely. I'll leave that kind of thinking to guys flying puddle jumpers !
You can go around from a floating 1 ft if you have to ( I've done it, I'm a rubbish pilot)just be aware that you can't haul the nose up until you're away and flying.
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Yes you can do it guys.....but why when you have a choice to do it earlier than 1ft ? Capt Fathom you are at much greater risk of striking the tail on Go-around rather than take off, the fact you can do both isn't the point. Its risk management. Rotating with landing flap is different to take off and affected by inertia, rotating with the oleos compressed on Go-around reduces tail clearance, the semi levered gear system is for take off only..... I could bore you with the technical however there are a number of carriers including more recently our Japanese friends who have scrapped the tail doing just that. Lets not forget a "normal" go-around is the most screwed up manoeuvre in the industry. How many times do pilots practice take offs compared to Go-arounds and how many practice it from a very low Go-around. That's why Boeing specifically caution it. I am in a fortunate position to see the fun on a weekly basis in the sim.
Last edited by 8che; 16th Oct 2015 at 10:55.
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Ok. Simple question. So you can land safely on a given runway at Vref40 + 40 with a flap problem, but you are not allowed to do a normal F40 landing with a 20kts tailwind. Why? It can't be the LDR because that issue is covered.
I agree with the comment about Rhodes, having been there is some nasty Wx. However, it is always the commander's decision to deviate from an SOP in the interests of safety. Is an ILS on 25 with an extra 2kts better than an NPA onto RW07. No question.
What did guys do before OFDM's & FMC's. Has our decision making been made easier or the opposite? Have these written limitations, in combination, inhibited sound judgement and decision making?
If you have a choice between a straight in landing ILS with 25kts tail on a long runway, or a scratch around on a circle in 3km's vis OVC500 at night to the opposite runway in a place you've never been before. Which would you consider safer? The other option is divert to somewhere with no crew or much chance of pax overnighting etc. etc.
The runway can be calculated as long enough via NNC QRH LDR's. It's the >10kts tailwind that is the gotcha, not LDA > LDR.
Remember this is a light hearted discussion. I doubt we are going to change any rules over night.
I agree with the comment about Rhodes, having been there is some nasty Wx. However, it is always the commander's decision to deviate from an SOP in the interests of safety. Is an ILS on 25 with an extra 2kts better than an NPA onto RW07. No question.
What did guys do before OFDM's & FMC's. Has our decision making been made easier or the opposite? Have these written limitations, in combination, inhibited sound judgement and decision making?
If you have a choice between a straight in landing ILS with 25kts tail on a long runway, or a scratch around on a circle in 3km's vis OVC500 at night to the opposite runway in a place you've never been before. Which would you consider safer? The other option is divert to somewhere with no crew or much chance of pax overnighting etc. etc.
The runway can be calculated as long enough via NNC QRH LDR's. It's the >10kts tailwind that is the gotcha, not LDA > LDR.
Remember this is a light hearted discussion. I doubt we are going to change any rules over night.
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Ok. Simple question. So you can land safely on a given runway at Vref40 + 40 with a flap problem, but you are not allowed to do a normal F40 landing with a 20kts tailwind. Why? It can't be the LDR because that issue is covered.
Also a flap problem with Vref40+40 landing would have been thoroughly briefed whereas a last minute tail wind excursion beyond limits might probably not.
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Don't take it too seriously. All I'm asking is; are you really jeopardising the a/c landing with a 'suspected' 13kts tailwind instead of a supposed limit of 10kts on a sufficiently long runway?
Remember this extra 3 kts people are talking about is derived from the FMC while still above flare height. If ATC said it was 13kts then the approach would become a discussion time even before it commenced.
This is really about the perceived safety v practical argument of GA or land decisions being made at very low level.
I suspect it will become an eternal circular discussion with no clear answer and up to the individual on the day. However, there seem to be some CP's who have devised an SOP to consult the magic box at DA; and some who have made it up themselves.
Remember this extra 3 kts people are talking about is derived from the FMC while still above flare height. If ATC said it was 13kts then the approach would become a discussion time even before it commenced.
This is really about the perceived safety v practical argument of GA or land decisions being made at very low level.
I suspect it will become an eternal circular discussion with no clear answer and up to the individual on the day. However, there seem to be some CP's who have devised an SOP to consult the magic box at DA; and some who have made it up themselves.