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Hot-Refueling - Is it safe?

With a piston engine - definitely not!!!! With a turbine engine, maybe.

More and more often I am seeing Robinson helicopters (not picking on Robinsons, they are just popular) being hot refueled at small airports. In most cases this happens at a self serve pump where the pilot lands, locks down the controls, and gets out and refuels himself. I was going to add herself, but I have never witnessed a female pilot doing this; perhaps they really are smarter. There is a HUGE difference between hot-refueling a turbine engine helicopter, and hot refueling a piston engine helicopter!! See below

What is the purpose of a hot refuel anyway? The pilots are in a hurry, plain and simple. Just this last week, a pilot was killed in east Tennessee while hot refueling a Bell 407; the rotor struck him in the head. Although this is a peculiar accident, accidents can and do occur. The fact of the matter is, you may get away with short-cutting safety procedures for a long time, then one day without warning, BANG! Without warning? NOT, you have been warned; you have common sense, that alone should prevent you from hot refueling a piston powered helicopter.

All piston engine helicopters have the fuel system located above the engine; why? Gravity, these engine are gravity fueled. No matter what, gravity will always do its thing when it comes to a spill. Some piston helicopters (Hughes/Schweizer/Bell 47) have a pan surrounding the fuel tank equipped with a drain spout with an outlet low on the airframe where if a leak develops the fuel will not spill onto the engine. After looking into this design and talking with some manufacturers, this pan is not intended to permit or encourage hot refueling. The Robinson R-44 has cowling surrounding the engine however the fuel source is still above the engine and hot refueling this aircraft is also extremely dangerous.

Argument in support of hot refueling has and will continue to come from some pilots. Regardless of these arguments, hot refueling is risky for many reasons and significantly more risky for piston helicopters than it is for turbines. The bottom line is that one must always weigh the risk against the gain. Even with these considerations, I doubt hot refueling a piston helicopter could ever be justified. Even in a turbine helicopter hot refueling should not occur unless there is a procedure in place which includes other support personnel for this operation. Some of the more significant differences between piston and turbine hot refueling are outlined below.

1. Turbine engines 'cycle out'. This means that unlike a piston engine which only times out, a turbine engine often requires overhauls based on the number of starts or 'cycles' as well as the time. This alone is not sufficient reason to hot refuel.

2. Turbine engines, unlike piston engines are positioned (in most cases) high above the fueling point with the exhaust stack pointing upwards and/or rearwards; consequently there is little danger of fuel being spilled onto the hot engine or exhaust stack (exception - MD helicopters). Piston engines are located low and usually below or inline with the fueling point which creates an extreme hazard when refueling due to the high probability of a spill and resulting fire/explosion.

3. Most turbine operators have a policy and procedure for 'Hot Refueling' if they permit it at all, which always includes more than one crew member. I am not aware of any operator who has a policy in writing permitting single pilot hot refueling. Most operators would fire a pilot for taking such a risk.

4. The flash point of AvGas is -20ºC while the flash point of Jet Fuel is 47-52ºC - A very important fact pointed out by a reader.

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Last modified: 01/19/08