Fuel Reserve Decision at a Remote Launch Site
You plan a 90-minute recreational flight from a private field 40 km from your home base. The balloon has two 40-litre propane tanks; pre-flight dip-tube check suggests tank A is about 70% full and tank B about 30% full. Burner consumption in still air averages 1.6 kg per 15 minutes of flight, plus roughly 0.4 kg per 100 m of initial climb. Forecast winds are light, but the only two suitable landing areas within 20 km are a harvested field and a narrow farm track. Your retrieve crew is a single vehicle with no trailer and must drive 35 minutes to reach you. The pilot's operating handbook lists a minimum landing reserve of 10% of total usable fuel.
1. Using the figures given, estimate total fuel available and the fuel needed for the planned flight, then state whether the flight should proceed as planned.
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Propane density is roughly 0.51 kg/L, so 80 L total capacity gives about 41 kg if both tanks were full. Tank A at 70% of 40 L is 28 L (about 14 kg); tank B at 30% is 12 L (about 6 kg). Total usable is therefore about 40 L, or roughly 20 kg, not 41 kg. Planned burn: 90 minutes at 1.6 kg per 15 minutes is 6 × 1.6 = 9.6 kg, plus an initial climb of, say, 500 m at 0.4 kg per 100 m = 2 kg, so about 11.6 kg. A 10% reserve of 20 kg is 2 kg, leaving 18 kg usable, which covers 11.6 kg with margin. The flight is feasible on fuel alone, but the margin is thin because the estimate depends on dip-tube accuracy. Recommend confirming tank contents by weight or refuelling before launch.
2. Identify the operational and regulatory factors, beyond fuel quantity, that should influence the go/no-go decision.
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The single-vehicle retrieve crew without a trailer is a significant constraint: if the balloon lands on the narrow farm track, recovery may block the road or require the crew to return with equipment. The 35-minute drive means the pilot may wait on the ground well beyond the flight time, which matters in heat or cold. Only two landing areas within 20 km limits options if winds shift; light winds can still drift the balloon away from both. The pilot should check that the chosen landing field has permission and is not a restricted or congested area, and should confirm the site is outside any aerodrome traffic zone. A formal risk assessment should weigh the thin fuel margin, limited landing options, and slow retrieval, and the pilot should be prepared to shorten the flight or cancel if any factor worsens.