CAP 697 MRJT FIG 4.4
FINAL RESERVE fuel is
calculated (for a turbojet) as 30 mins fuel at 1500ft above DESTINATION
ALTERNATE....hence your calculation is correct...destination alternate is at
30ft amsl, so you need 30 mins fuel at 1530ft (mass 50000kgs).
From the table – fuel
flow 2280 kg/hr, so FINAL RESERVE = 1180 kgs
They have offered
destination airfield elevation as a distraction - its irrelevant!