Fuel

Worked Examples — Fuel

The concept lesson Fuel — Time and Quantity explains EASA NCO.OP.125. Here are four worked examples.

Exercise 1: Simple day VFR flight

Task: C172 (cruise consumption 9 USG/h). Planned flight 1

Solution:

• Trip fuel: 1.5 h × 9 = 13.5 USG
• Taxi/start: 0.5 USG
• Contingency 5 %: 0.675 USG → 1 USG
• Final reserve (30 min day VFR): 0.5 h × 9 = 4.5 USG
• Total = 13.5 + 0.5 + 1 + 4.5 = 19.5 USG

C172 tank: 53 USG (50 usable) → ample. After fuelling to 30 USG the reserve is > 10 USG = >1 h flight time.

Exercise 2: Night VFR with short leg

Task: Diamond DA-40 (cruise consumption 7.5 USG/h). Planned flight 45 min night VFR.

Solution:

• Trip fuel: 0.75 h × 7.5 = 5.6 USG
• Taxi: 0.5 USG
• Contingency 5 %: 0.28 USG → 0.5 USG
• Final reserve (45 min night VFR!): 0.75 h × 7.5 = 5.6 USG
• Total = 5.6 + 0.5 + 0.5 + 5.6 = 12.2 USG

DA-40 tank: 50 USG → ample. Noteworthy: night reserve alone is as much as the flight itself.

Exercise 3: Longer flight with alternate

Task: PA-28 Cherokee 180 (consumption 10 USG/h). Plan: 2

Solution:

• Trip fuel: 2.25 h × 10 = 22.5 USG
• Taxi: 0.8 USG
• Contingency 5 %: 1.1 USG → 1.5 USG
• Alternate fuel: 0.5 h × 10 = 5 USG
• Final reserve (30 min day): 0.5 h × 10 = 5 USG
• Total = 22.5 + 0.8 + 1.5 + 5 + 5 = 34.8 USG

PA-28-180 tank: 50 USG (48 usable) → tight, but feasible. With stronger headwind or over-plan burn, could become critical.

Exercise 4: Range question

Task: C172 has 30 USG usable fuel on board. Cruise speed 100 kt GS, consumption 9 USG/h. How far can I go with reserve for 45 min (night VFR)?

Solution:

• Final reserve (45 min): 0.75 × 9 = 6.75 USG
• Trip fuel = 30 − 6.75 = 23.25 USG
• Flight time = 23.25 / 9 = 2.58 h ≈ 2 h 35 min
• Distance = 100 × 2.58 = 258 NM

→ Max range about 258 NM. Note: contingency (5–10 %) and taxi/start not subtracted — in practice subtract them! Realistic range closer to 220–230 NM.

Bonus: power-dependence of consumption

POH C172 (typical):

• 75 % power: about 9–10 USG/h, TAS about 110 kt → specific range about 11 NM/USG.
• 65 % power: about 8 USG/h, TAS about 105 kt → about 13 NM/USG.
• 55 % power: about 7 USG/h, TAS about 95 kt → about 13.5 NM/USG.

→ Best range at 55–65 % power, best time at 75 %, best comfort in between. Consult the POH!