on final approach

[AVIATROZ]

Q. on final approach ATC will inform crew of a change in wind velocity.
in case of a tailwind what change do they inform?

ans-
a. 4 kts
b. 5kts
c. 2 kts
d. 3 kts

ans is C. 2kts

plz explain what is the reason behind 2kts....

if the change in tailwind is of more than or less then 2 kts then...what they do

thanks for the help

[welliewanger]

Any tailwind will affect any landing significantly. Headwind has a similar effect but tailwind is more detrimental, causing the groundspeed to be higher, resulting in a longer landing distance.

Performance calculations should have been completed well before the approach and (in most public transport operations) there are significant safety margins. The reason for needing to know the wind moments before touchdown is that it changes the length (distance) of the flare. With slightly more tailwind, the flare is much longer. Without knowing of the increased tailwind the pilot may think he has overdone the flare and try to "put the aircraft down" resulting in an abrupt arrival.

HTH.

[fireflybob]

Kinetic energy is proportional to Speed squared!

In simple language, double the touchdown speed and you quadruple the energy you need to dissipate before stopping.

Small additions to the approach/touchdown speed have a large effect on landing performance.

[BOAC]

If the tailwind is very strong it can blow your flaps down.

[AVIATROZ]

firstly thanks for the reply fellow aviators...

i completely understand the effect of tailwind on our landing......firstly according to CARS we r nt suppose to land in direction where we get tailwind.....as it will increase our landing distance.....if winds r strong could even result in fatal consequences..

anyways....my doubt is with respect to the Question.......as in the question ..why the answer is 2KTS... why the other options are incorrect....

what happen if tailwind more than or less than 2 kts....then will atc inform abt it..

hope i was able to clear out what i wanted to ask

thanks

[welliewanger]

I'm pretty sure they'll inform you if the tailwind component changes by anything more than 2 knots.

[Spitoon]

In the UK ATC will give you the surface wind velocity (in most cases in the vicinity of the TDZ and averaged over 2 minutes) at some point - typically with the landing clearance if it issued while you are at a 'normal' range from touchdown - and any significant changes after that. Although there is a definition of what significant change is, controllers are generally quite aware when there is a tailwind on the approach or landing (or is important for some other reason) and will often pass windchecks when it may be useful for the crew. There is generally no obligation to report the tailwind component....or even to calculate it...and so an increase of 2kts or whatever will not necessarily be reported by ATC.

[Honey Monster]

If the tailwind is very strong it can blow your flaps down.

How? If an aircraft is in flight, it is moving forwards through the air mass.

I agree that when on the ground a strong tailwind can damage control surfaces, but the question was about an aircraft on final approach