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There are a number of clues that might prevent misfueling with jet fuel. I have read that certified aircraft are prevented by regulation from having the word "turbo" on the outside (see Tom's comment below). They also are required to have a filler neck too small for a jet fuel nozzle, and jet fuel nozzles are required to be larger. The fuel tank is supposed to be labeled. In testing the fuel one good reason to draw more than a token amount is to make sure you're not draining just the fuel that is right at the drain, but presumably the fuel in the tank will be mixed from the fueling process. This might not be true if you only top off with a small amount, but after refueling you should visually inspect the level, including a sniff at the filler and sticking a finger in the fuel. A mixture of jet fuel will be higher in viscosity than gasoline, so when you stir and dump it you should see a difference if there is a significant amount. The fuel will smell different and will evaporate slower. You should touch the fuel to see if it is cold and it shouldn't feel oily -it should evaporate leaving no residue. I believe you can buy fuel strainers designed to separate the two fuels. As for the original question about color, I'm not sure.
The bad news is that it only takes a small amount of jet fuel to lower the octane dramatically. The engine may start normally burning the gasoline that is in the lines and then could idle without a problem, especially if the engine is already warm. The problem may not be evident until the engine has been running at full throttle long enough for the cylinder temperatures to come up. Depending on the concentration of jet fuel in the gasoline the detonation could be light to severe, accompanied by pre-ignition and very high cylinder pressures, probably double normal. The smoke mentioned in the report is probably due to the slow evaporation of the fuel that results in rich pockets in the chamber, leaving the carbon. One could reduce the manifold pressure, leaving the rpm as high as possible, and hope then engine produces power long enough to get back. Left long enough (could be seconds or minutes) things start to break. How to detect it after starting the engine? There might be rough running and a stumble as throttle is applied. The exhaust temperatures will drop, probably erratically from cylinder to cylinder, and there should be audible detonation. Soon enough for an alert pilot to abort the takeoff? I have no idea. Hopefully the prevention and detection actions in the first paragraph will eliminate the final problem.
What color does 100LL turn if you mix in some Jet-A? Maybe we should add the "sniff test" to the preflight. We still take fuel samples as part of the preflight... right?
Mark S.
On Sat, May 3, 2008 at 11:13 PM, Tom Gourley < tom.gourley@verizon.net> wrote: isn't this the one the determined had been fueled with Jet-A instead of 100LL... apparently the FBO had also fueled a 421 at the same time with Jet-A, however it was caught prior to takeoff... I got this second hand so perhaps it is not correct? I don't know about the plane being misfueled, but this comment reminds me of something I read a while back. The pilot of a Turbo-Skylane was refueling while on a cross country trip and noticed the line guy was about to pump Jet-A into his plane. When the pilot stopped him from pumping the Jet-A the line guy, with a confused look on his face, said, "But it says Turbo on the side. Don't all these Turbos use Jet-A?" A good reminder that just because someone works around airplanes doesn't mean they know much about them. Keep a close eye on the fuel truck. And having the word "Turbo" prominently displayed on an airplane is not necessarily a good thing. Tom Gourley
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