Originally Posted by
flight01
3. If unable to comply with point (2)(a) above for the destination aerodrome where the appropriate weather reports or forecasts indicate that the runway at the Estimated Time of Arrival may be dry or wet and where a landing depends upon a specific wind component, the aeroplane shall not be dispatched.
4. If unable to comply with point (2)(a) above for the destination aerodrome where the appropriate weather reports or forecasts indicate that the runway at the Estimated Time of Arrival may be contaminated and where a landing depends upon a specific wind component, the aeroplane shall only be dispatched if two alternate aerodromes are selected which permits full compliance with all landing requirements above.
My 2¢ on why this makes sense (and wholeheartedly agree OM-As should be written in plain English a la Mr. Croucher...)
(2)(a):
Firstly, land on the most favourable runway (normally the longest) in still air.
If you cannot comply with (2)(a) but can comply with (2)(b), you have taken advantage of a strong headwind in order to apply the dispatch planning factors and land at an airport whereby under still wind you wouldn't be able to access. If it was just a case of having a forecast tailwind on the probable runway, you could still comply with (2)(a) and dispatch. If you cannot comply with (2)(a) then you are gaining a performance advantage purely from a strong headwind onto a runway that is marginal for your type and the regulations prevent you from having a go. Imagine R09, wet, wind 090/35 and the runway has an LDA of 2000m, and you have a still wind LDR of 2100m. Taking into account half the headwind, you now have an LDR of 1900m. The only way you can land on that wet runway is because of the headwind - you cannot satisfy (2)(a), so you can't go.
With a contaminated runway, I would suggest that braking action has a much greater effect on landing distance than 50% of the forecast wind, and as it is usually derived from dry/wet runway data with considerable factorisation is therefore much more of a guidance where you should tread with caution. Therefore dispatch is permitted with two alternates, and on you go, brave commander.