Hold or Divert With Alternate Fuel Protected
You are commanding a twin-jet from Kuwait (OKBK) to Dammam (OEDF). Planned figures: taxi fuel 200 kg, trip fuel 2,400 kg, contingency 5% of trip, alternate fuel to Bahrain 700 kg, final reserve 30 min at 1,200 kg/h, additional fuel 100 kg. Takeoff fuel is 4,300 kg. Forty nautical miles before Dammam, ATC puts you in a hold at 7,000 ft. The destination forecast is marginal and the expected hold is 25 min. Fuel flow in the hold is 2,400 kg/h. The first officer computes that you have 'about 40 minutes' before reaching final reserve and proposes to hold for the forecast 25 min. The weather at Bahrain is currently suitable, but a line of thunderstorms is approaching from the northwest.
1. Calculate the minimum required takeoff fuel and the actual fuel margin over that minimum.
Read the worked answer
Contingency = 5% × 2,400 = 120 kg. Final reserve = 30 min × 1,200 kg/h = 600 kg.
Minimum takeoff fuel = taxi 200 + trip 2,400 + contingency 120 + alternate 700 + final reserve 600 + additional 100 = 4,120 kg.
Actual takeoff fuel is 4,300 kg, so the margin over the planned minimum is 4,300 − 4,120 = 180 kg. That margin is not available for a 25 min hold; it is the only discretionary buffer above the plan.
2. Calculate the maximum hold time that still protects alternate fuel and final reserve, and decide whether to hold for 25 min.
Read the worked answer
Fuel at destination before holding = 4,300 − 200 taxi − 2,400 trip = 1,700 kg.
To divert to Bahrain and land with final reserve intact you must keep 700 + 600 = 1,300 kg. Fuel available for holding = 1,700 − 1,300 = 400 kg.
At 2,400 kg/h, 400 kg lasts 400 ÷ 2,400 = 0.167 h = 10 min. Holding 25 min would burn 1,000 kg, leaving only 700 kg; after the 700 kg diversion you would arrive with zero fuel and no final reserve. The first officer's 40 min figure probably uses only final reserve (1,700 ÷ 2,400 ≈ 42 min) and ignores the alternate.
Decision: do not hold for 25 min. Divert now toward Bahrain while the weather is still suitable, or hold for no more than about 10 min if ATC can guarantee immediate onward clearance. Given the approaching thunderstorms, the safer judgement is to divert now rather than burn the protected alternate fuel.