I'm currently in the process of refining a planning system for a couple of specialist users, who use an earlier Airbus type.
I note from the FCOM Vol. 2 that:
- No destination to alternate diversion fuel planning figures are published for diversion distances of less than 100nm.
- No corrections for head/tail wind component are published for diversion distances of less than 200nm.
- The flight profile assumes that the diversion to the alternate will be flown at long range cruise speed at not less than FL100.
- A VFR approach is assumed.
- Corrections must be made for deviation from reference landing weight, ISA deviation, use of anti-icing and use of 'normal' air conditioning.
Using the destination-to-alternate planning tables for a 150 nm diversion (roughly the same as Madrid to Valencia), the minimum fuel state at which to commence the go-around at destination in order to arrive at the alternate with final reserve only is 4589 kg, assuming landing at the alternate at the reference landing weight. However, Spain with summer thunderstorms? If you assume you're stuck down at FL100 and are given an extra 50 nm of vectoring, might well need engine anti-icing and normal air conditioning in ISA+15 conditions, plus an IFR approach at the alternate, the figure rises by another 1080 kg....
What assumptions are normally made for diversions to alternate aerodromes these days? I imagine that some flight dispatch organisation plans the fuel required, but do they take
everything into account, or just use the basic figure corresponding to the optimum diversion flight level and direct distance?