Fuel Load Decision on a Short Sector
A twin-engine transport is scheduled for a 95-minute sector. Its planned fuel is: trip fuel 2,400 kg, contingency 10% of trip fuel, alternate fuel 700 kg, final reserve 900 kg, and taxi fuel 120 kg. Total fuel on board at start-up is 5,000 kg. During taxi, a 40 kg spill-free burn occurs as planned, but the crew is then told the destination weather is at the edge of the alternate minima and they must hold for 15 minutes at 1,600 kg/hour. The aircraft's maximum landing weight permits a landing with no more than 4,600 kg remaining. The captain argues they can accept the hold because 'we still have contingency and final reserve untouched.'
1. Compute the minimum required fuel for the original plan and the fuel remaining after the unplanned 15-minute hold. Does the captain's argument hold?
Read the worked answer
Original minimum fuel:
- Trip = 2,400 kg
- Contingency = 10% × 2,400 = 240 kg
- Alternate = 700 kg
- Final reserve = 900 kg
- Taxi = 120 kg
- Total = 2,400 + 240 + 700 + 900 + 120 = 4,360 kg
Fuel on board 5,000 kg gives an extra 640 kg above minimum.
After taxi and hold:
- Taxi burn = 120 kg → 4,880 kg at take-off
- Trip burn = 2,400 kg → 2,480 kg at destination
- Hold = 15 min × 1,600 kg/h = 400 kg → 2,080 kg on arrival at the alternate decision point
Check against reserves: alternate (700) + final reserve (900) = 1,600 kg needed. Remaining 2,080 kg leaves only 480 kg above the protected reserves - i.e. contingency has already been eaten into (240 kg) plus 240 kg more.
Verdict: The captain's claim is wrong. The contingency is a planning buffer, not a hold allowance. The hold consumes 400 kg, of which only 240 kg was contingency; the rest comes out of the margin above final reserve. A 15-minute hold is legal only if the extra 400 kg is available above the 4,360 kg minimum - here the surplus is 640 kg, so the hold is just feasible, but any further delay, extra approach, or go-around would breach final reserve. The correct call is to reduce payload or add fuel before departure, or plan a diversion.
2. The maximum landing weight limits landing to 4,600 kg remaining. Recheck the landing weight after the hold and state the operational implication.
Read the worked answer
After hold, fuel remaining at destination = 2,080 kg (from previous task).
Landing weight = operating empty weight + payload + fuel remaining. The problem does not give OEW or payload, so we cannot compute absolute landing weight - but we can note that the fuel component is 2,080 kg, which is 480 kg above the protected reserve of 1,600 kg.
If the aircraft's landing weight with 2,080 kg of fuel is at or below 4,600 kg, the landing is legal. If it exceeds 4,600 kg, the crew must either burn fuel (hold longer) or divert to a closer airfield. This is a classic trap: the hold that protects reserves can push landing weight above MLW on a short sector with a heavy payload.
Implication: The crew should compute landing weight before accepting the hold, not after. If MLW is the binding limit, the correct action is to reduce payload or plan a diversion, not to rely on 'contingency and final reserve' as if they were free fuel.