Helicopter Flight Information

Hot Refueling Helicopters - Is it safe?

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

Turbine aircraft with low mounted engines such as MD/Hughes helicopters, the new Robinson R66, and perhaps a few others fall under the definitely not category as well.  Interestingly enough, I have had a few emails requesting that I note that with proper procedures and training, hot refueling a piston engine helicopter is safe.  I can not make such note since there is no scenario which makes hot-refueling these aircraft safe, sensible, or worth the risk.

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 which is even more foolish and dangerous.  I was going to add herself, but I have never witnessed a female pilot doing this; perhaps they really are smarter.  There have however been cases where the FBO staff actually conducted the hot refuel in piston aircraft such as is common practice at the Pahokee airport in Florida.  Obviously they have not considered the hazard, or pilots have snowed them into thinking that it is safe.  No FBO should permit its staff to hot fuel any aircraft without proper training.

What is the purpose of a hot refuel anyway?  The pilots are in a hurry, plain and simple.  Recently 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, and this was not the first and it won't be the last.  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 should have been born with some common sense and 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 may not spill onto the engine.  This pan does not in anyway prevent the flow of fuel vapors which are far more explosive than liquid fuel.  After looking into this design and talking with some manufacturers, this pan is not intended to permit nor 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.  Fuel fumes spread very rapidly, are very explosive, and are invisible until they ignite.

Argument in support of hot refueling has and will continue to come from some pilots.  Regardless of these arguments, hot refueling is unacceptable in piston powered helicopters for many reasons.  The bottom line is that hot refueling a piston helicopter could never 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 the 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, and many pilots do not understand the cycle out count.  Generally speaking, if there are more cycles on the engine than hours, the engine will cycle out; if there are less cycles than hours, the engine will time out.  In the later case cycling out is then a mute point since it will not occur.

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/Hughes and the Robinson R66 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/or fuel vapor drift which could result in a fire/explosion.

3. Most turbine operators have a policy and/or procedure in place, 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 permitting single pilot hot refueling.  Most operators would fire a pilot for taking such a ridiculous risk.  There is no policy or procedure which could justify, or make safe, the hot refueling of a piston powered helicopter, period.

4. The flash point of AvGas/Gasoline is -46ºC (-51ºF) while the flash point of Jet Fuel is +38ºC (+100ºF) - Per the MSDS provided by Chevron Oil Company (100LL Jet Fuel); a very important fact pointed out by a reader.  Also, the ignition of jet fuel vapor is not likely to occur, while the ignition of gasoline vapors is extremely easy and very likely to occur.

There is a HUGE difference between hot-refueling a turbine engine helicopter if the engine is located above the fuel tank, and hot refueling a piston engine helicopter!!

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Last modified: 12/31/2011