Free safety module 5 of 7Flight Planning & Airmanship11 min readLast reviewed: 2026-09-13
Build a fuel plan that meets CASR Part 91, carry the correct final reserve, and run disciplined en-route fuel checks so a stronger-than-forecast headwind never becomes a fuel emergency.
Scenario
Headwind Stronger Than Forecast on a Marginal-Range Leg. You planned Bathurst (YBTH) to Coonabarabran (YCBB) then Moree (YMOR), about 2 h 50 min in total, in a Cessna 182 by day VFR, carrying trip fuel plus the 30-minute final reserve. Levelling at cruise you find a 25 kt headwind rather than the forecast 10 kt. At the first fuel check overhead Coonabarabran, fuel remaining is 15 minutes below plan and the gap is widening each leg.
Decisions and actions
Plan to land with the final reserve untouched (CASR Part 91 MOS chapter 19): 30 minutes for a piston or turboprop aeroplane of 5,700 kg or less by day VFR; 45 minutes by night VFR or IFR; 20 minutes for a helicopter by VFR.
Recalculate at the groundspeed you are actually achieving: fuel to destination at the observed headwind, compared with fuel remaining minus the final reserve.
Nominate an en-route aerodrome for a fuel diversion and set the trigger before you need it — "if fuel remaining reaches X litres at this point, divert".
Log a fuel check at every waypoint: time, fuel remaining, fuel used against plan, and revised endurance. A written trend makes the divert decision obvious.
Safety traps
Planning to "fuel on board" rather than "usable fuel above the final reserve".
Plan-continuation bias: treating the destination as fixed once airborne despite a widening fuel deficit.
Unusable fuel, tank imbalance and gauge error eroding the real margin.
A low-level diversion, richer mixture or carburettor heat increasing fuel burn above the planning figure.
Check your understanding
1. What final fuel reserve must a piston-engine aeroplane of 5,700 kg or less plan to land with on a day VFR flight?
45 minutes, remaining in the tanks on landing
30 minutes, remaining in the tanks on landing
10 per cent of the trip fuel
Enough fuel to return to the departure aerodrome
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B. The Part 91 MOS sets the final reserve for a piston or turboprop aeroplane of 5,700 kg or less at 30 minutes by day VFR and 45 minutes by night VFR or IFR. It is fuel you plan to land with, not fuel to use in flight.
2. Your en-route fuel checks show fuel remaining below plan, with the gap growing each leg. What is the safest response?
Lean the mixture aggressively and continue to the planned destination
Continue, and reassess when the low-fuel warning appears
Divert now to a nominated en-route aerodrome while fuel remaining still covers the diversion plus the final reserve
Increase cruise speed to arrive sooner
Show answer
C. Decide on the trend, not the warning light. Divert while the numbers still close with the final reserve intact. Flying faster usually increases total fuel burn.
Educational use only. This module does not replace current legislation, the AIP, ERSA, authorised weather briefings, the aircraft flight manual or instructor guidance. Verify operational information through official sources before flight.
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