A320 Flex temperature tailwind
 

Hello folks,

What influence has a 5 kts tailwind on the performance calculation. Any rule of thumbs like without tailwind 55 and with a tailwind of 5kt then 45. I want to know in case of short notice of the tailwind and we can take a formula to do a quick change.

Thanks!

Sw

There is no rule of thumb. Takeoff performance can be limited by any of several factors: TODA, ASDA, second segment climb performance, obstacle and so on... You really can`t use any rule of thumb to predict how the 5kt tailwind will influence the takeoff performance in any given case.

Use TOGA!?!? LOL!

Why not just write down the corrections on a piece a paper (from your OFP TLR) and keep it handy. If the tower informs you of a tailwind, just make the corrections on the PERF page. Shouldn't take more than 10 seconds...

What if your headwind decreased by 5kts? What if wind changed direction by 20-30 degrees? What if wind changes during the takeoff run? You can`t really take into account any wind variation. What is a chance that actual wind during takeoff will be exactly the same as given in ATIS?

That's why the performance calculation uses 50% the head wind or 150% of the tailwind in the maths.

Worst case is a calm wind in the maths, then you pick up a tailwind during the take off.

If conditions vary that much (variable winds on the ATIS, thunderstorms in the area etc), then surely, as an experienced pilot you would have calculated the takeoff with a tailwind!

If you're operating out of an airport with a long runway, sea level, no obstacles and so on, your 5 kt tailwind might not do too much for you. But if you're about to takeoff from a short runway, or a high elevation airport, or terrain is a concern, you either have a set of calculations previously done handy or you advise ATC you're not ready to depart and run a new calculation. It takes 30 secs on the FlySmart thingy.

Don't modify the performance numbers so arbitrarily, especially on a high performance aircraft. Too many factors contribute to a takeoff to "just add/subtract 5 kts for this or that"

I have just looked at our paper performance charts for Birmingham. At low weights flex stays the same, at medium weights 5kt tail reduces flex by 2 or 3 degrees and towards the upper end it reduces by 6 degrees until it becomes a performance limit. There is no rule though and you should compute performance from a chart or the flysmart app.

As Penko rightly says apply the KISS principle and, if variable conditions, just use a tailwind in the initial calcs.

If conditions change dramatically then stop and re do the calcs, it doesn't take that long even without the flysmart software.