Hot Fueling 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.
(In the photo, R66 engine positioned low and aft, the Hughes/MD and Bell 47 turbine installations are similar.) More and more I'm seeing piston helicopters, a lot of them Robinsons, being hot fueled 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 fuels himself which is even more foolish. I was going to add herself, but I haven't witnessed a female pilot doing this. There have been cases where the FBO staff were the ones actually conducted the hot fueling in piston aircraft such as is common practice at the Pahokee airport in Florida. Either they haven't considered the hazard, or pilots have snowed them into thinking that it's safe.
No FBO should permit its staff to hot fuel any aircraft without proper training, but more importantly they should never hot fuel any gas powered aircraft.
What is the purpose of a hot fuel anyway? The pilots are in a hurry, plain and simple. Sometimes it may be justifiable, and sometimes not. I have hot fueled a plenty on jobs such as ENG where you are under pressure to get back to a scene, or EMS where you have a critical paitent on board, etc. In my earlier and more foolish days, I may have even hot fueled a piston helicopter, but I don't recall it. If your life is worth that little, knock yourself out. Just don't take anyone else with you, and don't deceive those who don't know any better.
A pilot was killed in east Tennessee while hot fueling a Bell 407 where the rotor struck him in the head. Although this is a peculiar accident, accidents can and do occur. This was not the first and as long as people do stupid things, 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! You should have been born with some common sense and that alone should prevent you from hot fueling a piston powered helicopter. It takes 2-minutes or less to shut down, and less than 2-minutes to start any 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. This pan is not intended to permit nor encourage hot fueling. The Robinson R-44 has cowling surrounding the engine, however the fuel source is still above the engine and hot fueling this aircraft is also extremely dangerous. The fumes of gasoline spread very rapidly, are very explosive, and are invisible until they ignite.
Argument in support of hot fueling has and will continue to come from some pilots. Regardless of these arguments, hot fueling is unacceptable in piston powered helicopters for many reasons. The bottom line is that hot fueling a piston helicopter could never be justified. Even in a turbine helicopter hot fueling 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 fueling are outlined below.
- Turbine engines cycle out - Unlike a piston engine which only times out, a turbine engine often requires overhauls based on the number of starts (aka cycles) as well as the time. This alone is not a sufficient reason to hot fuel, 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.
- Turbine engines are positioned high - With some exceptions, most turbine engines are located 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 (exceptions - MD/Hughes, Bell 47, Robinson R66). Piston engines are located low and usually below or inline with the fueling point which creates an extreme hazard when fueling due to the high probability of a spill and/or fuel vapor drift which could result in a fire/explosion.
- Strict Procedures -Most turbine operators have a procedure in place for hotfueling 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 fueling. 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 fueling of a piston powered helicopter, period.
- The flash point of fuels - The flashpoint 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). Also, the ignition of jet fuel vapor is not likely to occur, while the ignition of gasoline vapors is extremely explosive and very likely to occur.
There is a HUGE difference between hot fueling a turbine engine helicopter if the engine is located above the fuel tank, and hot fueling a piston engine helicopter!! END Jump to Top