Strong head wind on approach
Guest
Posts: n/a
Health Warning
It seems to me that safe flying involves the intelligent use of heuristics (the application of principles and guidelines), but there can be a tendency for people to wish to avoid uncertainty and ambiguity by using algorithms instead (rules - e.g. if this happens do that)
Furthermore, there is a strong element of situational awareness required in flying, combined with the ability to make the appropriate decision.
In my limited amount of flying, I can think of two occasions where I made diametrically opposed decisions when encountering windshear on very short final, each being ok in the context.
Join Date: Mar 2002
Location: Euroland
Posts: 2,814
Likes: 0
Received 0 Likes
on
0 Posts
Well said John Farley!
All this talk about adding extra speed just because the wind is strong will end up causing an accident either because;
1. The approach speed is too fast and the aircraft arrives nosewheel first as the pilot tries to drive it on; or
2. The pilot avoids driving it on and floats off into the hedge at the far end.
Windspeed usually decreases with decreasing height. Yes if one starts an approach at 2000ft and never monitors the airspeed, then one could end up with a much lower speed by 100ft. However, provided that the airspeed is monitored and corrections made, then one can never have that problem.
However, when the wind is gusting then we know that there may be sudden unexpected changes in both windspeed and direction. In that case, some increase in airspeed is sensible and the figure I use is half the reported gust.
A greaser landing is not a good landing if it happens at the end of a 200m float!!
-----
A stalled aircraft is not in my opinion out of control provided the pilot is competent. One has placed the aircraft in a stall and one can by simple movement of the controls get the aircraft out of the stall again. Thus control is available. What one can say however is that the flight path is unpredictable while the aircraft is stalled.
There is a big difference between "releasing the back pressure" and "pushing the nose down".
Remember also that the aircraft stalls at a particular angle of attack not at a particular airspeed. Thus should one be flying an approach at 5Kt above the normal approach speed, if one snatches the control stick back to arrest a sudden increase in descent one can exceed the stall angle of attack at that speed.
Regards,
DFC
All this talk about adding extra speed just because the wind is strong will end up causing an accident either because;
1. The approach speed is too fast and the aircraft arrives nosewheel first as the pilot tries to drive it on; or
2. The pilot avoids driving it on and floats off into the hedge at the far end.
Windspeed usually decreases with decreasing height. Yes if one starts an approach at 2000ft and never monitors the airspeed, then one could end up with a much lower speed by 100ft. However, provided that the airspeed is monitored and corrections made, then one can never have that problem.
However, when the wind is gusting then we know that there may be sudden unexpected changes in both windspeed and direction. In that case, some increase in airspeed is sensible and the figure I use is half the reported gust.
A greaser landing is not a good landing if it happens at the end of a 200m float!!
-----
A stalled aircraft is not in my opinion out of control provided the pilot is competent. One has placed the aircraft in a stall and one can by simple movement of the controls get the aircraft out of the stall again. Thus control is available. What one can say however is that the flight path is unpredictable while the aircraft is stalled.
There is a big difference between "releasing the back pressure" and "pushing the nose down".
Remember also that the aircraft stalls at a particular angle of attack not at a particular airspeed. Thus should one be flying an approach at 5Kt above the normal approach speed, if one snatches the control stick back to arrest a sudden increase in descent one can exceed the stall angle of attack at that speed.
Regards,
DFC
Join Date: May 2002
Location: Sale
Posts: 375
Likes: 0
Received 0 Likes
on
0 Posts
Buy a copy of "Stick and Rudder". All will be revealed.
Easily the best flying book in my collection. I wish I'd read it before I started my flight training.
I personally like the authors use of "Savages" in one of his analogies.
FIS.
Easily the best flying book in my collection. I wish I'd read it before I started my flight training.
I personally like the authors use of "Savages" in one of his analogies.
FIS.
Why do it if it's not fun?
Join Date: Jul 2001
Location: Bournemouth
Posts: 4,779
Likes: 0
Received 0 Likes
on
0 Posts
John F,
Your "health warning" is very well placed - and in fact applies to just about everything which any pilot, low hours or not, reads on PPRuNe or anywhere else. The rules are simple - never try anything new by yourself!
But I, for one, would not want such health warnings to put an end to this type of discussion. There is always more than one way to skin a cat, and one of things I love about flying is that the people who do it love talking about it, talking about the way they fly, the techniques they use, and the pros and cons of the various techniques.
Haul,
Agree with Kingy's reasoning on why this is such an important subject. To add to his points, though, I'd also suggest that when you've practiced stalling at altitude, you've could well have been trimmed for cruising speed, whereas on final approach you will (hopefully) be trimmed for the approach speed - a speed which is much closer to the stall, and therefore requires much less effort to inadvertantly enter a stall. Also, most trainers are (for fairly obvious reasons) designed to be difficult to stall inadvertantly, which may not be the case for some other aircraft.
Your "health warning" is very well placed - and in fact applies to just about everything which any pilot, low hours or not, reads on PPRuNe or anywhere else. The rules are simple - never try anything new by yourself!
But I, for one, would not want such health warnings to put an end to this type of discussion. There is always more than one way to skin a cat, and one of things I love about flying is that the people who do it love talking about it, talking about the way they fly, the techniques they use, and the pros and cons of the various techniques.
Haul,
Agree with Kingy's reasoning on why this is such an important subject. To add to his points, though, I'd also suggest that when you've practiced stalling at altitude, you've could well have been trimmed for cruising speed, whereas on final approach you will (hopefully) be trimmed for the approach speed - a speed which is much closer to the stall, and therefore requires much less effort to inadvertantly enter a stall. Also, most trainers are (for fairly obvious reasons) designed to be difficult to stall inadvertantly, which may not be the case for some other aircraft.
Do a Hover - it avoids G
Join Date: Oct 1999
Location: Chichester West Sussex UK
Age: 91
Posts: 2,206
Likes: 0
Received 0 Likes
on
0 Posts
Hi everyone
The topic of this thread has still got to be dealt with regardless of whether one normally practices speed control via the stick or via the throttle. So let us try and avoid being deflected into which technique is the better, either on a normal approach or when in very strong headwind conditions.
I’m sure we can all agree that the problem with a very strong headwind is that it is likely to include gusts and so give you a seriously fluctuating ASI. The other possibility is that there will be a dramatic AND SUSTAINED reduction in the wind speed close to the ground perhaps in the last 200 feet or so, just when things are getting tense.
The problem as ever breaks down into two parts, the approach and the landing.
So far as the approach is concerned it is obviously possible to fly a suitably increased IAS so that the reading at the bottom of the flicks does not go below what you are normally happy to see on the approach and also includes some fat for a susequent severe wind sheer.
As has been pointed out, doing this does raise the issue that you MIGHT finish up much too fast in the flare and be tempted to throw it on the ground nose low and weak nose leg first. This is dangerous as we all know. Whether you have the ability to complete a fast safe and easy approach BUT still hold off and stay just clear of the ground until speed and attitude are normal for touchdown only you know. If you are doubtful then a diversion to a less demanding location would be nice IF the option exists. A less demanding location could be one with the same wind speed but less gustiness due to local buildings trees etc. It could also be a much longer runway where you can treat the approach like a forced landing and aim your approach well into the strip, so that should you touch down before you intended you are still going to be on the proper stuff and not in the undershoot.
If there is no runway length issue then most manuals will suggest reducing the flap – perhaps even to zero – giving the aeroplane a more nose up attitude at touchdown than would be the case with full flap. This is good because it reduces the risk of hitting the nosewheel during any last moment thrashing about and will also make the aeroplane settle more positively on to the ground and reduce the chance of it being blown about at the start of the roll out. Like everything though, if you cannot remember the last time you did a flapless landing your lack of currency could compound the weather issues.
Point one. Don’t plan to fly in strong winds unless you are in practice with reduced flap landings and don’t let your reduced flap landings get well out of currency just because there has been no wind for the last three times you flew.
Point two. Brief yourself on the downwind leg (God look at this groundspeed) to be ready to overshoot if it gets too gusty even if the approach seems reasonable. Again only you will know what level of being tossed about will concern you but if it does bother you then round you go because you may be luckier with the wind next time.
Point three The only time you should ever feel hesitant to go round is if the fuel is terribly low, the wind is forecast to get worse quickly or it is nearly dark In no other circumstances should any press on element be allowed to creep in.
Point four. If despite all the precautions you get suddenly and unexpectedly caught out close to the ground with an airspeed that seems half of what it should be, slam full power and maintain the sort of nose position you would associate with touch down. Then if you do sink to the surface you have done what you can to give the gear a chance to save the day, while if you don’t actually touch and it starts to go around well that is great. Just great.
The topic of this thread has still got to be dealt with regardless of whether one normally practices speed control via the stick or via the throttle. So let us try and avoid being deflected into which technique is the better, either on a normal approach or when in very strong headwind conditions.
I’m sure we can all agree that the problem with a very strong headwind is that it is likely to include gusts and so give you a seriously fluctuating ASI. The other possibility is that there will be a dramatic AND SUSTAINED reduction in the wind speed close to the ground perhaps in the last 200 feet or so, just when things are getting tense.
The problem as ever breaks down into two parts, the approach and the landing.
So far as the approach is concerned it is obviously possible to fly a suitably increased IAS so that the reading at the bottom of the flicks does not go below what you are normally happy to see on the approach and also includes some fat for a susequent severe wind sheer.
As has been pointed out, doing this does raise the issue that you MIGHT finish up much too fast in the flare and be tempted to throw it on the ground nose low and weak nose leg first. This is dangerous as we all know. Whether you have the ability to complete a fast safe and easy approach BUT still hold off and stay just clear of the ground until speed and attitude are normal for touchdown only you know. If you are doubtful then a diversion to a less demanding location would be nice IF the option exists. A less demanding location could be one with the same wind speed but less gustiness due to local buildings trees etc. It could also be a much longer runway where you can treat the approach like a forced landing and aim your approach well into the strip, so that should you touch down before you intended you are still going to be on the proper stuff and not in the undershoot.
If there is no runway length issue then most manuals will suggest reducing the flap – perhaps even to zero – giving the aeroplane a more nose up attitude at touchdown than would be the case with full flap. This is good because it reduces the risk of hitting the nosewheel during any last moment thrashing about and will also make the aeroplane settle more positively on to the ground and reduce the chance of it being blown about at the start of the roll out. Like everything though, if you cannot remember the last time you did a flapless landing your lack of currency could compound the weather issues.
Point one. Don’t plan to fly in strong winds unless you are in practice with reduced flap landings and don’t let your reduced flap landings get well out of currency just because there has been no wind for the last three times you flew.
Point two. Brief yourself on the downwind leg (God look at this groundspeed) to be ready to overshoot if it gets too gusty even if the approach seems reasonable. Again only you will know what level of being tossed about will concern you but if it does bother you then round you go because you may be luckier with the wind next time.
Point three The only time you should ever feel hesitant to go round is if the fuel is terribly low, the wind is forecast to get worse quickly or it is nearly dark In no other circumstances should any press on element be allowed to creep in.
Point four. If despite all the precautions you get suddenly and unexpectedly caught out close to the ground with an airspeed that seems half of what it should be, slam full power and maintain the sort of nose position you would associate with touch down. Then if you do sink to the surface you have done what you can to give the gear a chance to save the day, while if you don’t actually touch and it starts to go around well that is great. Just great.
Spoon PPRuNerist & Mad Inistrator
A number of people have enquired what glider pilots do with headwinds - JF mentions it in his point 2:
Basically, observe what is happening and take account of the conditions by edging in, turning base much earlier, turning finals earlier, as there is no second chance. Airbrakes / flaps not deployed until certain of making the field.
The approach speed (ias) is not necessarily higher, the rate of descent is not greater, but the angle of descent relative to the ground is higher.
If anyone wants to experience a really fabulous approach in a glider, fly a ridge soaring site like Camphill (DLGC) where a strong westerly produces great ridge lift but wicked curlover (rotor downdrafts) - the "clutching hand" - for landings. In a 15-20 kt headwind, the glider approach speed is 80-85 kts where it would normally be 50-55 (1.3 vs) and the angle of descent is Stuka-like! However, I emphasise that this is because of the SINK, not the headwind per se.
The first time you see it you just do not believe that the glider is going to stop before running over the edge and down into the valley below
- of course it rolls to a stop less than half way there! I don't think anyone has floated over the edge, but loads of people have undershot!
SD
Brief yourself on the downwind leg (God look at this groundspeed)
The approach speed (ias) is not necessarily higher, the rate of descent is not greater, but the angle of descent relative to the ground is higher.
If anyone wants to experience a really fabulous approach in a glider, fly a ridge soaring site like Camphill (DLGC) where a strong westerly produces great ridge lift but wicked curlover (rotor downdrafts) - the "clutching hand" - for landings. In a 15-20 kt headwind, the glider approach speed is 80-85 kts where it would normally be 50-55 (1.3 vs) and the angle of descent is Stuka-like! However, I emphasise that this is because of the SINK, not the headwind per se.
The first time you see it you just do not believe that the glider is going to stop before running over the edge and down into the valley below
- of course it rolls to a stop less than half way there! I don't think anyone has floated over the edge, but loads of people have undershot!SD
We fly in 30, 40 & even 50 kt winds into short & often very turbulent strips. What John says is very true.
I often find myself needing full power then almost immediately idle and often back again. In general my target speed is the normal approach speed adjusted upwards so that a sudden wind speed reduction (ie an undershoot shear) isn't sufficient to stall (yeah, yeah, AoA is correct but I don't have an AoA indicator).
The goal is to keep the speed in a 'reasonable place'. Accept that it will not be constant but try to keep the median where you want it.
This leaves the problem of a fast approach speed. At some point you have to reduce to some semblance of a landing speed.
Limiting flap helps for the reasons John said. It also has the advantage that a higher IAS is needed for the a/c to fly so that acts in your (currently too fast) favour. The higher nose attitude adds some leeway to a fast touchdown without wheelbarrowing. In other types full flap has the advantage of allowing you to quickly wash off the extra speed during the flare, so a fast approach may not be all that problematic.
Generally a 'fly the mainwheels straight onto the runway' rather than a pronounced hold off/float.
There will still be a need to close the throttle & lose some speed. The timing of this comes down to judgement on the day. The stronger the headwind the more power is needed to maintain the approach path to the aiming point, and the later the power reduction will be needed when there. The more turbulance then also the later. It's not fun to be hung up at 20' at idle just as an undershoot shear arrives.
Be prepared to use up to full power to cushion a touchdown OR to go around. I've had instances where I'd set up to touchdown just as a strong gust arrived (or departed...) and needed immediate power to cushion the arrival. Others warranted direct to a max performance go around at the attitude for Vy & max power.
It pays to know the airstrip. It may have a particular part of the runway that is prone to some very nasty shear depending on wind direction & strength and another section that is often clear. It's easy enough to plan to land on a different section of the runway that you know is likely clear of the turbulance inducing terrain or in the lee of a large sheltering object. Even on very short runways. How much length do you require for your a/c type with a 30 or 50 kt headwind component?
At an unfamiliar strip it can be beneficial to make practice approache(s) to get an idea about where the shear starts & the strength.
It can be......erm......character building.
Just my thoughts...
I often find myself needing full power then almost immediately idle and often back again. In general my target speed is the normal approach speed adjusted upwards so that a sudden wind speed reduction (ie an undershoot shear) isn't sufficient to stall (yeah, yeah, AoA is correct but I don't have an AoA indicator).
The goal is to keep the speed in a 'reasonable place'. Accept that it will not be constant but try to keep the median where you want it.
This leaves the problem of a fast approach speed. At some point you have to reduce to some semblance of a landing speed.
Limiting flap helps for the reasons John said. It also has the advantage that a higher IAS is needed for the a/c to fly so that acts in your (currently too fast) favour. The higher nose attitude adds some leeway to a fast touchdown without wheelbarrowing. In other types full flap has the advantage of allowing you to quickly wash off the extra speed during the flare, so a fast approach may not be all that problematic.
Generally a 'fly the mainwheels straight onto the runway' rather than a pronounced hold off/float.
There will still be a need to close the throttle & lose some speed. The timing of this comes down to judgement on the day. The stronger the headwind the more power is needed to maintain the approach path to the aiming point, and the later the power reduction will be needed when there. The more turbulance then also the later. It's not fun to be hung up at 20' at idle just as an undershoot shear arrives.
Be prepared to use up to full power to cushion a touchdown OR to go around. I've had instances where I'd set up to touchdown just as a strong gust arrived (or departed...) and needed immediate power to cushion the arrival. Others warranted direct to a max performance go around at the attitude for Vy & max power.
It pays to know the airstrip. It may have a particular part of the runway that is prone to some very nasty shear depending on wind direction & strength and another section that is often clear. It's easy enough to plan to land on a different section of the runway that you know is likely clear of the turbulance inducing terrain or in the lee of a large sheltering object. Even on very short runways. How much length do you require for your a/c type with a 30 or 50 kt headwind component?
At an unfamiliar strip it can be beneficial to make practice approache(s) to get an idea about where the shear starts & the strength.
It can be......erm......character building.
Just my thoughts...
Join Date: Aug 2002
Location: Manchester, England
Posts: 102
Likes: 0
Received 0 Likes
on
0 Posts
Another factor to think about this time of year on grass runways is the reduced directional control you have when the surface is muddy. I landed in a G115 at Barton yesterday into a strong headwind varying about the runway heading, on the rollout the a/c drifted towards the left edge despite full right rudder and differential braking, simply through the weathercocking effect and the nosewheel sliding sideways.... To make my embarrassment complete the left wheel ended up in a rut and it took full power and tapdancing on the brakes to get moving again to vacate. It seems that in strong crosswinds the rollout is sometimes more exciting than the touchdown.
