Overweight at Density Altitude
A private pilot is planning a local flight with two friends in a balloon whose placard lists a maximum gross weight of 1,500 lb. The empty weight, including envelope, basket, burner, and empty tanks, is 760 lb. The pilot weighs 190 lb; passenger A weighs 220 lb; passenger B weighs 180 lb. Propane aboard is 60 lb, and equipment (instruments, fire extinguisher, anchor, miscellaneous gear) weighs 55 lb. The field elevation is 4,200 ft MSL, the temperature is 30°C, and the altimeter is 30.05. The pilot calculates a density altitude of approximately 6,800 ft. The manufacturer's performance chart in the balloon manual shows that, at that density altitude with the burner at its maximum continuous temperature, the envelope can lift 1,350 lb. The pilot plans a one-hour flight and wants a 30-minute reserve. Average propane consumption is 12 lb per hour. The pilot considers leaving passenger B behind or waiting until evening, when the temperature is forecast to be 18°C.
1. Compute the total loaded weight and compare it with the maximum gross weight and the lift available at the forecast density altitude. Is the flight legal and safe?
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Total weight = 760 + 190 + 220 + 180 + 60 + 55 = 1,465 lb. Maximum gross weight is 1,500 lb, so the balloon is 35 lb under the placarded limit. That does not make the flight safe or legal in the performance sense. The manufacturer's chart shows only 1,350 lb of lift at the calculated 6,800-ft density altitude with the burner at maximum continuous temperature. The load exceeds available lift by 1,465 − 1,350 = 115 lb. At that density altitude the balloon cannot lift the load without exceeding the burner's continuous limit, which is not an acceptable workaround. The controlling limit is performance, not just structural maximum gross weight. The pilot should not launch.
2. If the pilot offloads passenger B (180 lb), will the flight be within limits? Show the new weight and the margin.
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New total with passenger B off = 1,465 − 180 = 1,285 lb. Maximum gross margin = 1,500 − 1,285 = 215 lb under. Lift margin = 1,350 − 1,285 = 65 lb under the charted lift. That is a positive margin, so the flight is feasible at the planned density altitude, assuming the chart is accurate and the burner performs as expected. Propane check: 60 lb at 12 lb/hr gives 5 hours total; 1 hour flight + 0.5 hour reserve = 1.5 hours, requiring 18 lb. 60 lb is ample. The pilot should still confirm basket loading and balance, and use the actual temperature at launch rather than the forecast.
3. What if the pilot instead waits until evening at 18°C? Estimate qualitatively how density altitude and lift change, and whether that is a safer option than offloading a passenger.
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Waiting until 18°C lowers the density altitude. A rough estimate: pressure altitude is about 4,070 ft; at 18°C the temperature is about 11°C above ISA, which adds roughly 1,300 ft, giving a density altitude near 5,400 ft. Air density and lift increase, perhaps by 8–10%, so charted lift might rise to about 1,460–1,485 lb. That is only marginally above the 1,465-lb load, so the pilot would still need to verify with the chart and could be at the edge of performance. Offloading passenger B gives a clearer 65-lb lift margin and is the more predictable choice. Waiting also introduces evening wind and stability changes. The safer decision is to offload weight or use a larger envelope, not to rely on a temperature forecast.