correction for tail wind on approach
Thread Starter
Join Date: Oct 2011
Location: sky
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
correction for tail wind on approach
My Co. says add 1/3 head wind to approac speed or 1/2 gust, limited to max 15 kts.
My question is what to do in case of tailwind or gusting tailwind?
My question is what to do in case of tailwind or gusting tailwind?
Join Date: Sep 2005
Location: ???
Posts: 260
Likes: 0
Received 0 Likes
on
0 Posts
Or if you do land with a steady tailwind and it is within the aircraft limit you don't add any wind correction same for crosswind. The reason you add the correction due to the headwind is in case the headwind component suddenly drops during the approach. if it does drop by half then your IAS will momentarily drop to your vref speed.. ie still safe.
If that happens with the tailwind component it will only serve to increase your IAS which might destabilise your approach but at least you won't run the risk of stalling on short final.
If that happens with the tailwind component it will only serve to increase your IAS which might destabilise your approach but at least you won't run the risk of stalling on short final.
My question is what to do in case of tailwind or gusting tailwind?
Join Date: Feb 2001
Location: Milkway Galaxy
Posts: 240
Likes: 0
Received 0 Likes
on
0 Posts
All commercial types advises to increase the approcah speed by a certain factor depending on headwind (e.g 1/3 f HW component).
"Mistakenly" it is considered a safety factor to overcome a sudden decrease in HW, as protecting the normal app speed (KIAS).
No, this is not correct, it may be only a side effect.
The main reason: As increasing the App speed depending on HW, the cockpit view (cut off angle) remains same for a fixed path approach. For example in an ILs approach with 3 degrees, if the same app speed is maintained regardless of a strong headwind, body attitude (but not AOA) would be higer than normal, as reducing the cockpit view through windshield.
"Mistakenly" it is considered a safety factor to overcome a sudden decrease in HW, as protecting the normal app speed (KIAS).
No, this is not correct, it may be only a side effect.
The main reason: As increasing the App speed depending on HW, the cockpit view (cut off angle) remains same for a fixed path approach. For example in an ILs approach with 3 degrees, if the same app speed is maintained regardless of a strong headwind, body attitude (but not AOA) would be higer than normal, as reducing the cockpit view through windshield.
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes
on
0 Posts
Hi flyburg,
Don't loose any sleep trying to get your head around that one - it doesn't make any sense to me either.
if the same app speed is maintained regardless of a strong headwind, body attitude (but not AOA) would be higer than normal, as reducing the cockpit view through windshield.
Join Date: Sep 2000
Location: London, England
Posts: 185
Likes: 0
Received 0 Likes
on
0 Posts
On a 3 degree slope, if you have a strong HW but use the same airspeed, the groundspeed will be lower, therefore required vertical speed lower (approx 3 time G/S?) so there will be a slightly higher nose attitude. If you are a bus driver you can watch the "ground speed mini" function add lots of airspeed in a strong headwind and see the lower nose attitude. However i do not understand how this would affect the cut off angle being talked about significantly as a one or two degree pitch change would not obscure the view of the runway. eg when landing with flap 3 instead of full on an A320, the pitch attitude is about 5 degrees instead of 2.5 but does not affect the view of the runway threshold?
Also no knowledge of what to do with a gusting tailwind other than land the other way.
Also no knowledge of what to do with a gusting tailwind other than land the other way.
Join Date: Nov 2000
Location: Netherlands
Posts: 254
Likes: 0
Received 0 Likes
on
0 Posts
Hi rudderrudderrat, thanks, but too late, haven't closed an eye 
guess I feel pretty stupid but even with above explanation can't figure it out. I know you need more power in a strong HW. Am I correct in stating that the added HW introduces a vector which actually changes your path in space but not when related to the GP? That is the only thing that makes sense.
Have to admit, never gave too much thought to it, just did it but interesting nonetheless!
Actually fatflyer, one or two degrees will make a difference on the ground segment you would be able to see. Groundsegment being the distance on the ground limited by your forward visibilty and the cutoff angle. One of the reasons when visibility is low we usually use flaps 30 instead of 25 when landing. Pfft, I did know that one
guess I feel pretty stupid but even with above explanation can't figure it out. I know you need more power in a strong HW. Am I correct in stating that the added HW introduces a vector which actually changes your path in space but not when related to the GP? That is the only thing that makes sense.Have to admit, never gave too much thought to it, just did it but interesting nonetheless!
Actually fatflyer, one or two degrees will make a difference on the ground segment you would be able to see. Groundsegment being the distance on the ground limited by your forward visibilty and the cutoff angle. One of the reasons when visibility is low we usually use flaps 30 instead of 25 when landing. Pfft, I did know that one
Last edited by flyburg; 1st Nov 2011 at 13:20.
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes
on
0 Posts
Hi flyburg,
If you had a huge head wind during your ILS App, so that your ground speed was zero, then you'd apply more power and have to fly level to stay on the ILS glide path. Your pitch attitude would be 3 degs higher than normal, so the view out of the window would show the runway apparently 3 degs lower than normal. But by increasing the approach speed, you could lower the nose and still fly level, and help restore the normal picture.
If you had a huge head wind during your ILS App, so that your ground speed was zero, then you'd apply more power and have to fly level to stay on the ILS glide path. Your pitch attitude would be 3 degs higher than normal, so the view out of the window would show the runway apparently 3 degs lower than normal. But by increasing the approach speed, you could lower the nose and still fly level, and help restore the normal picture.
Last edited by rudderrudderrat; 1st Nov 2011 at 15:15. Reason: spelling
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,507
Likes: 0
Received 0 Likes
on
0 Posts
To expand the question into the performance and legal envelope: I have tried for many years to get an official answer from my company on the legal question of gusty tailwind limits. No success yet. You have a 10 or 15kt tailwind legal limit and no option for the other rwy. The ATC wind is 13G25kts and it is a -15kt approved rwy. Can you land legally? Simple question; at least I thought so. No problem with the company answering the X-wind question, but this one has been filed in a black-hole. The performance dept says they would use all the gust for landing distance calculations, but that was not the question. Is it legal to land? Even the manufacturer says it is up to the airline, except the airline is keeping it secret. Can anyone help?
Join Date: Feb 2001
Location: Milkway Galaxy
Posts: 240
Likes: 0
Received 0 Likes
on
0 Posts
Hi flyburg,
Sorry for this confusion.
I cannot give any written reference but, on a delivery flight of a B 737-800 in Seattle, one of the Boeing Engineer who is in charge of documentation, he explained one of our question regarding the speed selection difference between B 737-400 and 800 by this way. Frankly speaking, even I forgot what was our question then so he explained this way (long time I am flying with Airbus 330, so the concept is completely different).
But my humble knowledge of Aerodynamic and Flight Mechanic confirms what the engineer said, as simply explained by Fatflyer. If we look the things in the reverse way, this also explains why there is so small tailwind limit (usually 10 K) regardless of the length of runway where we land (even so long): Because in the HW case you can compansate body attitude by increasing speed, but in TW case you do not have this option as reducing speed below Vref. Result, at very strong tailwind you may hit the nose gear before main gear.
The Airbus Document "Getting the Grips with Cat II and III" explains how the visual segmet is effected by body attitude. As you are aware, 1 or 2 degrees changes of attitude by speed may seem small, but its impact on visual segment (particularly at high cockpit airplanes) will be more pronounced.
Maybe some other collegues can explain better.
Regards
Sorry for this confusion.
I cannot give any written reference but, on a delivery flight of a B 737-800 in Seattle, one of the Boeing Engineer who is in charge of documentation, he explained one of our question regarding the speed selection difference between B 737-400 and 800 by this way. Frankly speaking, even I forgot what was our question then so he explained this way (long time I am flying with Airbus 330, so the concept is completely different).
But my humble knowledge of Aerodynamic and Flight Mechanic confirms what the engineer said, as simply explained by Fatflyer. If we look the things in the reverse way, this also explains why there is so small tailwind limit (usually 10 K) regardless of the length of runway where we land (even so long): Because in the HW case you can compansate body attitude by increasing speed, but in TW case you do not have this option as reducing speed below Vref. Result, at very strong tailwind you may hit the nose gear before main gear.
The Airbus Document "Getting the Grips with Cat II and III" explains how the visual segmet is effected by body attitude. As you are aware, 1 or 2 degrees changes of attitude by speed may seem small, but its impact on visual segment (particularly at high cockpit airplanes) will be more pronounced.
Maybe some other collegues can explain better.
Regards
Join Date: Feb 2001
Location: Milkway Galaxy
Posts: 240
Likes: 0
Received 0 Likes
on
0 Posts
From the equation given above, an example:
ILS GS=3 deg, TAS=140 and HW= 30K,
Then Air GS =2.35 deg,
Any idea about the required pitch change to reduce Air GS from 3 deg to 2.35 deg (equal to change of the flight path 0.65 deg)?
It may not be necessarily equal to 0.65 deg pitch change, could be greater...
ILS GS=3 deg, TAS=140 and HW= 30K,
Then Air GS =2.35 deg,
Any idea about the required pitch change to reduce Air GS from 3 deg to 2.35 deg (equal to change of the flight path 0.65 deg)?
It may not be necessarily equal to 0.65 deg pitch change, could be greater...