1 — Fuel Is Time, and Fuel Is Mass
Fuel exhaustion is one of the most preventable causes of accidents — it is an arithmetic problem, not bad luck. Two ideas from earlier lessons meet here: fuel is time (litres ÷ fuel flow = hours, from Lesson 4) and fuel is mass (litres × density = kg, which you loaded in Lesson 6).
2 — What Are the Part-NCO Fuel Blocks?
Part-NCO builds your total — the block fuel — from named pieces. Everything except extra is the legal minimum to depart.
- Taxi — fuel to start, taxi and run up before takeoff.
- Trip — climb, cruise and descent to the destination.
- Contingency — a margin for the unexpected (winds, routing); commonly about 5% of trip fuel.
- Alternate — trip fuel on to an alternate aerodrome, when one is planned.
- Final reserve — the protected block you must still have on landing (next section).
- Extra — discretionary fuel the pilot-in-command adds on top.
3 — What Is the Final Reserve Fuel Rule?
The final reserve is the line you never plan to cross. Under EASA Part-NCO (NCO.OP.125) it depends on the flight — least for a local flight in sight of the field, most for night or IFR:
AMC1 NCO.OP.125(b). The 10-minute case applies only to a local VFR-day flight — take-off and landing at the same aerodrome, staying in sight of it. A normal cross-country needs 30 minutes by day, 45 by night or IFR (at holding speed, 1 500 ft above the destination).
4 — Plan Your Fuel
Every block comes from the same arithmetic: fuel = time × fuel flow. Set a trip and watch the blocks add up, against 120 L of usable fuel:
| Item | Litres |
|---|
Illustrative figures (taxi 3 L, 120 L usable). Real planning uses your aircraft’s POH and the current Part-NCO rules.
5 — Worked Example & the Golden Rules
Trip 80 min at 30 L/hr, 5% contingency, no alternate, VFR by day, taxi 3 L:
- Trip: 80 ÷ 60 × 30 = 40 L.
- Contingency: 5% × 40 = 2 L.
- Final reserve (day): 30 ÷ 60 × 30 = 15 L.
- Taxi: 3 L. Minimum block = 3 + 40 + 2 + 15 = 60 L (≈ 43 kg — carry that figure into your weight & balance).
6 — Fuel by Phase, and the Fuel Log
Treating the trip as one average flow is fine for a rough figure, but the POH actually gives a different fuel flow for each phase — and a careful plan writes them into the fuel section of the navigation plan, the fuel log:
| Phase / block | Basis | Fuel (L) |
|---|---|---|
| Engine start, taxi & run-up | fixed allowance | 3 |
| Climb | 10 min × 36 L/h | 5 |
| Cruise | 62 min × 30 L/h | 31 |
| Descent | 11 min × 22 L/h | 4 |
| Trip fuel | climb + cruise + descent | 40 |
| Contingency | 5% of trip | 2 |
| Final reserve | 30 min (VFR day) | 15 |
| Block fuel | minimum to depart | 60 |
The POH gives a fuel flow for each phase — climb runs richer (higher flow), descent leaner — so trip fuel is really climb + cruise + descent, not one average. Start/taxi/run-up is a fixed allowance the engine burns before trip fuel begins. Add contingency, alternate (if any) and the final reserve to reach block fuel — the figure you load and feed into mass & balance.
