Vapp in gusty conditions
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Vapp in gusty conditions
Confirm, you add the headwind component and half the gust factor to Vref to get a increased Vapp in gusty conditions; e.g, RWY36, Wind 270/16, gusts up to 24 kts, Vref: 108 kts. 8 kts. (=headwind component) + 4 kts. (=halft the gust factor) are added. Vapp: 108kts.+8 kts.+4 kts.=120 kts. Vref remains unchanged.
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Cecco
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Cecco
Depends on type and AFM or FCOM; more accurately on it's certification standard. The two types I fly, GLEX and CL 605, the GLEX the addditive is only 1/2 the gust; the CL 605, it is 1/2 the prevailing wind and all the gust.
GF
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For the Boeing 737:
Default calm wind minimum Vapp = Vref+5kts.
...then adjusted for half the headwind component and the full gust component, aggregate total adjustment not to exceed Vref + 20kts.
Landing performance allows for the gust component to be carried on top of Vref to the point of touchdown if preferred, but the headwind component should have diminished by the 50' Vref point.
Vref is nominated but not adjusted.
These procedures come from both Boeing's FCTM and 2 different airlines, but check your own manuals for what applies for your type.
Default calm wind minimum Vapp = Vref+5kts.
...then adjusted for half the headwind component and the full gust component, aggregate total adjustment not to exceed Vref + 20kts.
Landing performance allows for the gust component to be carried on top of Vref to the point of touchdown if preferred, but the headwind component should have diminished by the 50' Vref point.
Vref is nominated but not adjusted.
These procedures come from both Boeing's FCTM and 2 different airlines, but check your own manuals for what applies for your type.
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A quick question whilst on this topic. Would you apply these corrections to the wind vector reported by tower whilst commencing approach or to the wind vector calculated by the onboard computer? In the latter, wouldn't it keep changing as you're approaching the ground so would need to constantly adjust your Vapp?
I think 
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Mohit C you raise a very valid point.
I'm not aware of anything published in this regard. Personally, and others may disagree, I use the TWR reported wind components. If the components increase during the approach, I might announce to my colleague that I am increasing the factor and ask him to re-bug the new Vapp (if I am flying manually). But, good CRM and practicality would dictate this is not something changed every few seconds during the approach. Once the factor is added on it is arguably better to stick with it if the wind decreases. Who's to say the wind won't increase again? Performance figures (B737) tolerate this with the caveat of never exceeding Vref+20kts.
I'm not aware of anything published in this regard. Personally, and others may disagree, I use the TWR reported wind components. If the components increase during the approach, I might announce to my colleague that I am increasing the factor and ask him to re-bug the new Vapp (if I am flying manually). But, good CRM and practicality would dictate this is not something changed every few seconds during the approach. Once the factor is added on it is arguably better to stick with it if the wind decreases. Who's to say the wind won't increase again? Performance figures (B737) tolerate this with the caveat of never exceeding Vref+20kts.
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No it's just a crosswind. I can't see where the headwind he got came from. I guess technically there would be a tiny headwind I suppose as you turn into it to allow for drift but not practically speaking
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Boeing require the half the HW component is to be bled off on final so the aircraft crosses the threshold at Vref plus gust factor. Few operators actually do that in practice, which goes some way to explaining why the excess speed especially on a slippery runway, can lead to a long float and subsequent landing, and danger of running off the end.
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B717 FCOM, all gust, plus 1/2 steady state wind component above 20 kits, to a max 20 kg additive, with a min additive of 5 kits.
Eg, 30 kt wind gusting 45 kts would be 5 kts (30-20 = 10 & 1/2 of 10 = 5) plus 15 kts gust, for a total Vapp of +20.
Eg, 30 kt wind gusting 45 kts would be 5 kts (30-20 = 10 & 1/2 of 10 = 5) plus 15 kts gust, for a total Vapp of +20.
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A quick question whilst on this topic. Would you apply these corrections to the wind vector reported by tower whilst commencing approach or to the wind vector calculated by the onboard computer? In the latter, wouldn't it keep changing as you're approaching the ground so would need to constantly adjust your Vapp?
BTW, our company policy is either the full wind above 20 kts, OR 1/2 gust factor, whichever is HIGHER. Minimum Vref+5, maximum Vref+20.
G.
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Keep in mind that the protocol is a bit rubbery -
(a) the steady wind is presumed to reduce within the notional boundary layer so it probably will drop off approaching the runway - the half factor attempts to handle this in some sort of rational way
(b) the gust is presumed to be random so it might catch you out at any stage of the approach - better to allow for all of it through to the landing
(c) 20kt max tries to balance having too much against too little IAS approaching the runway
Nothing at all terribly scientific in this stuff - just an attempt to load the dice in the pilot's favour.
A few other threads on the subject have more description on the considerations for those interested in running a search.
(a) the steady wind is presumed to reduce within the notional boundary layer so it probably will drop off approaching the runway - the half factor attempts to handle this in some sort of rational way
(b) the gust is presumed to be random so it might catch you out at any stage of the approach - better to allow for all of it through to the landing
(c) 20kt max tries to balance having too much against too little IAS approaching the runway
Nothing at all terribly scientific in this stuff - just an attempt to load the dice in the pilot's favour.
A few other threads on the subject have more description on the considerations for those interested in running a search.
I have to say I've never been too worried about getting these additives exactly right, seeing as on many types if you've got the autothrottle in, you don't apply them. I feel most pilots can do a better job with the thrust than the autothrottle can, anyway...
For most landings, you have a good power-to-weight ratio (<MLW) and, *if you're stable*, can regain airspeed pretty quickly if necessary. The spread of speeds available is generally only 15kts, from Vref+5 to Vref+20. When Vref is 150kts+, I don't feel the need to add much more, especially if the runway is approaching limiting length. Overruns due to excess speed on T/D, prolonged flares, wet runways, tailwinds, etc. are right up there on the list of accidents that keep repeating themselves...
If it's a gusty day, keep on top of it!
For most landings, you have a good power-to-weight ratio (<MLW) and, *if you're stable*, can regain airspeed pretty quickly if necessary. The spread of speeds available is generally only 15kts, from Vref+5 to Vref+20. When Vref is 150kts+, I don't feel the need to add much more, especially if the runway is approaching limiting length. Overruns due to excess speed on T/D, prolonged flares, wet runways, tailwinds, etc. are right up there on the list of accidents that keep repeating themselves...
If it's a gusty day, keep on top of it!
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Right!
Hi full wings,
I generally agree. However, the computed Vappr values to me are max values.
Repeat: MAX!!!!
I've seen so many mates who do a great job in telling me what their Vappr would be; only to then add 5 for grandma, another five to "play it safe" and sometimes more for their inaptness. And they wonder why I would not let them fly when things get interesting and/or RWYlength is restricted...
Aside: yes, flying manually with autothrust engaged is calling for trouble.
To me it is a no-no.
Else: on many airports you have a windsock close to the touch down zone. To me this is providing the only true information- opposed to 10 min old TWR wind or IRS-derived erroneous winds. Use it! And your brain...
I generally agree. However, the computed Vappr values to me are max values.
Repeat: MAX!!!!
I've seen so many mates who do a great job in telling me what their Vappr would be; only to then add 5 for grandma, another five to "play it safe" and sometimes more for their inaptness. And they wonder why I would not let them fly when things get interesting and/or RWYlength is restricted...
Aside: yes, flying manually with autothrust engaged is calling for trouble.
To me it is a no-no.
Else: on many airports you have a windsock close to the touch down zone. To me this is providing the only true information- opposed to 10 min old TWR wind or IRS-derived erroneous winds. Use it! And your brain...
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Aside: yes, flying manually with autothrust engaged is calling for trouble.
Thanks in advance
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