Wind?

[littlejet]

If we are applying 1/2 HWC plus the entire gust value to Vref (in my company), why shouldn't we do it to V1, VR or V2 since those speeds are also IAS.
Imagine T/O wit MTOW with HWC 30 kt/gusting up to 45. What will happen to V2 if that wind suddenly drops?

L.

[Gary Lager]

JAR regs say that you can only take account of 50% of any HW component. That correction is already likely to be incorporated in your company Takeoff Perf procedures - TW must be considered as 150% of reported.

THis doesn't mean that you have to do a correction, more usually that the '10kts Headwind' figures you use have actually been calculated for 5kts headwind, and for with 10kts TW, the figures are calculated with 15kts etc.

I certainly wouldn't use any reported gust factor when calulating my RTOW, so any gust you do experience is a bonus in your favour, the absece of which should not affect your performance calculations.

Gusty conditions and knowing when to 'call' V1/VR can be tricky - use your common sense and exercise good airmanship when operating in these conditions. Making corrections to the speeds without a proscribed procedure for doing so could have all kinds of other ramifications (Vmca, Vmbe, etc) so be very wary of doing so.

Actually ,in your example (being pedantic) your V2 will stay exactly the same, but your current airspeed relative to that V2 will fall - that's called windshear. There are certain techniques which can and should be applied when those circumstances are expected, some prior to takeoff, precisely for the reasons you suggest (e.g. using full rated thrust instead of reduced/derate, not considering all the headwind component as usable when calculating RTOW etc. etc.).

[DC-Mainliner]

...What will happen to V2 if that wind suddenly drops?
L.

Exactly as Gary syas, if V2 drops significantly, you have winshear and a recovery process to initiate.

Remeber however, you may fly V2 to V2 plus a speed factor additive if you are already there, to a maximum of fifteen knots in a OEI scenario. If you have a windshear event OEI, then you are having a bad day, but you still have to fly the airplane and do the best you can.

As far as V1 goes, this is a ground distance issue for rejected takeoffs and continued takoffs with OEI. No gust factor, no additive, nothing like this at all! If V1 is adjusted it must be done only per procedure, not on a whim, or it could add unscheduled, spectacular light and smoke shows to the nearby airport residents. :ouch:

[PEI_3721]

A wind gust correct normally applies to the approach and then only before the threshold. Remember that the wind profile and gust characteristics vary with altitude, generally reducing the closer you are to the ground.
Takeoff V speeds are performance speeds which must be followed accurately in the event of an engine failure. There are safety margins within these speeds but not as great as the margin on Vref for landing (never more than +15 at the threshold, and then only with an accurate touchdown point). The takeoff speeds safety margin is to cover your flying errors and stall protection, not for additives.

[411A]

On one approach to GQNN not all that long ago, the First Officer was flying.
The reported wind was 'calm' but clearly there was an active windshear area on approach, as the airplane was well below the glidepath at 1000AGL, then high at 500AGL.
Yet, the young lad was flying....Vref.
Hmmm, me thinks, this should be interesting.
Approaching the threshold, clearly we are too high, so he goes around.
A proper decision.
Full marks for him.
I then suggest an automatic approach/land, as the landing runway was served by an ILS.
Sliding down the glidepath on the second approach, he notes the airspeed is Vref +40, decreasing to Vref+20 across the fence.
He wonders why...why so much airspeed at 500AGL?
Why indeed.
Simply because...the aeroplane is the superb Lockheed TriStar, and with its (IIRC) 16 accelerometers in the autothrust system, it absolutely does a better job.
And...another convert to the very best that there is...Lockheed TriStar.

He flies the next two sectors as well, and finds that he is no match for the Lockheed automatics.

When the chips are down, couple it up and watch PFM at work.
Takeoff?
See previous comments.
No additives are needed, nor necessary.

Lockheed...simply superb:D
It doesn't get any better.

[galaxy flyer]

411A:

The TriStar might be the greatest kite ever, but you need to speak with your employer about some of the places you're going? Yuck!!

At the other Lockheed widebody, we added the gust increment to V1 up to refusal speed. Made for a huge penalty in critical field length, not infrequently to make CFL = TORA. We also added gust to V2. No, I don't know why; yes, it was penalizing on perf.; no, they didn't need to make a profit. So there!

GF

[gearpins]

speed corr to Vref is to ensure a minimum energy level ( grd.spd) to take you to touch down, so that when thrust is removed and flared the a/c does not fall off the sky.
V2 is IAS with a minimum of 20% margin on Vs.(effect of wind/gust is on grd spd ).hence such a correction is not required