I buy FlightDetent's explanation.... ONE runway being with only one landing direction available. Hence, very special circumstances and to prevent the operation to
routinely circumvent the dispatch requirement, by selecting 2 alternates, to an airport that basically can
never be used according to the dispatch criteria.
What is practical is another discussion (one landing direction or not). Our performance software naturally calculates dispatch and inflight distances. However, if the dispatch requirement can't be met, it outputs "Landing weight too high for LDA", and doesn't calculate inflight either.
So what to do?? Flying into e.g. a 1700 meter runway, in a 738, fully loaded and with wet runway: Dispatch requirement is 1900 meters, ALD is 1300 (approx. values from the top of my head, don't beat me up if the percentages don't add up).
Software refuses to make any calculations! Solution is to chose another airport, with a longer runway and with similar pressure altitude and slope. I presented this problem to my Director of Flight Ops, and his reply was: "if it is wet, when you arrive, I recommend you divert!". If he doesn't want to take the chance, why should I?
400 meter margin may sound like a lot, but is it? Those ALD performance figures are not real, they were never demonstrated properly. The aircraft manufacturer is allowed to combine the best segments from different flights: Best flare, best touch down, best braking - and add each up a combined ALD. The PERFECT (unachievable) landing, made by a test pilot, with no regard for pax comfort and probably with little fear of making a hard landing and damage to the aircraft. Probably they had perfect tires and brakes installed as well.
Do you really want to try replicate than?
Personally, I do not need to sh!t my pant, and max effort braking coming to a halt with the nose hanging over the opposite approach lights.
