Hello all! I have a query re landing charts and the wind to use.

In an exam, conditions at the destination could be provided in the form of a TAF or just "given". My understanding was that if in a TAF, any headwind should not be factored in when calculating landing distance (or max landing weight). However, if just "given" (ambient conditions, I suppose), then it can be.

Now I've been trying to find the reference for this... but no luck. So I'm wondering if someone can help me out. Is this indeed a requirement and what is the reference/authority, or am I mistaken.

Thanks!

OK, I think I've found it in CAO 20.7.4: If using a TAF, consider temperature and pressure (or approved declared conditions) but not wind

In an exam, therefore, if a TAF is provided we should assume nil wind, but if wind is given (say "120deg M at 20kt") then we should include head/tai-wind in calculating landing distances or max landing weight.

The main driver for incorporating wind in the calculations has always been that old buzzword "commonsense". There used to be words in the rules about some of this but, along with many things, a lot has gone out in the bathwater along with the baby.

General philosophy has always been to be conservative or, if you like, mitigate against inadvertently being non-conservative.

Hence, with a TAF which, after all is only a technically competent "best guess", one needs to make reasonable allowance for the TAF's not being the story when one gets to the destination. Accordingly, at the planning stage, usual practice is to

(a) check the numbers on the main (longest suitable) runway for nil wind but also, if the TAF suggests a crosswind in excess of the aircraft's maximum on the main runway,

(b) check the numbers on a suitable subsidiary runway with the forecast wind to provide a fallback in the event that the TAF wind does eventuate at the time of arrival. Clearly, if there is no suitable subsidiary runway, one would be a bit foolhardy not to carry either an alternate or sufficient holding fuel to cover the TAF periods of interest..

Hi John. Yes, that makes complete sense! Right now I'm wanting to make sure I've got my methodology precisely correct for the exam, in which case I need to be clear if the wind is provided in a TAF (follow CAO 20.7.4 - longest RWY and nil wind) or as given (use given wind).

I'm a tad out of touch with what the examiner's precise expectations might be .. Bob probably is the man of the day for that, I suggest.

"Given" wind, one presumes, is that provided by the local ATC/observer.

The crosswind consideration used to be prescribed but the memory cells are not up to recalling a reference .. which is dead now, in any case.

The way I interpret that one is that if the flight is landing weight limited, then you cannot take-off on a weight that will cause the aircraft to be above the landing weight when it arrives at the destination. You would have to establish the landing weight BEFORE you took off. In that case, you do not use the wind. It's asking too much to rely on a 15kt wind to be blowing when you cross the fence on final.

Note that this paragraph in the CAO is under TAKE-OFF WEIGHT considerations. On the other hand, if a question simply asked you to calculate the maximum landing weight under a specific set of environmental conditions, then you would use the wind.

You can always use the wind for determining take-off weight because you cannot take-off unless you are present. All take-offs are optional - you don't have to take off if you don't like the wind component....