On March 2, 2008, a turbonormalized Cirrus SR22 was destroyed when it crashed shortly after takeoff in Rio de Janeiro, Brazil, killing all four people aboard. Shortly after the aircraft departed from Runway 20, the airplane’s engine lost power, and the aircraft hit a building and exploded. Further investigation revealed that the aircraft had been refueled with Jet A instead of 100LL.This report reminded me of an incident 16 years earlier during which my own 1979 Cessna T310R was misfueled with Jet A at San Carlos (Calif.) Airport, a busy GA airport just south of San Francisco. Fortunately, I caught the (mis)fueler in the act, red handed. Had I not been lucky enough to do that, I probably wouldn’t be writing this column.Normally, I either fuel my aircraft myself (at a self-serve pump) or watch it being fueled (when avgas is supplied by truck). On this occasion, I’d radioed for the fuel truck and waited patiently for it to arrive. After 10 minutes of waiting, Mother Nature intervened and compelled me to walk into the terminal building in a rather urgent search of a loo. By the time I took care of my pressing business and returned to the ramp, there was a fuel truck parked by my airplane and a lineperson pumping fuel into my right main tank. As I approached the aircraft, I observed to my horror that the truck was labeled “JET A.”
At first, I was not too worried, because I believed that misfueling my airplane with Jet A was physically impossible. That’s because in 1987 (the year I purchased my T310R), all turbocharged twin Cessnas became subject to Airworthiness Directive AD 87-21-02, which mandated installation of restrictor ports on all fuel-filler openings. The restrictor ports were designed to make it impossible to insert an industry-standard Jet A nozzle, while accommodating the smaller diameter avgas nozzle.The AD was issued because the FAA became aware that a large number of misfueling incidents and accidents were occurring in turbocharged aircraft. These aircraft typically were prominently decorated by the factory with the word “Turbo” and apparently linepeople were confusing it with “Turbine” and pumping Jet A into the tanks.So the FAA mandated that jet-fuel trucks install a wide, spade-shaped fuel nozzle, and that vulnerable airplanes (like turbocharged twin Cessna) have restrictor ports installed into which the wide jet-fuel nozzle would not fit. This made misfueling of piston aircraft with jet fuel theoretically impossible. (They also say that it’s theoretically impossible for bumblebees to fly.)But as I arrived at my airplane, I discovered that, indeed, my left main tank had been topped with Jet A. How was this possible? A subsequent investigation by the local FSDO revealed that the Jet A fuel truck at San Carlos Airport had not been fitted with the correct spade-type nozzle. (I suspect they got in trouble for that.)
Undoing The Damage
I spent literally hours trying to find an A&P on the field that would assist me in purging the fuel system of its witches’ brew of 100LL and Jet A. That turned out to be surprisingly difficult. The fueling company was falling all over itself to be helpful (because I’m sure they feared a big lawsuit) but they had no mechanics or maintenance capabilities. There were several maintenance shops on the field, but none wanted to go near my contaminated airplane, clearly afraid of the potential liability exposure. Finally, I persuaded one maintenance manager to help me out after writing and signing an omnibus waiver absolving the shop and its mechanics of any liability in connection with their work on my aircraft.The purging process itself was quite an eye opener. We drained the tanks as completely as possible, putting the noxious effluent into a 55-gallon drum provided by the fueling company (who had agreed to deal with the costly disposal of the nasty stuff). We disconnected the fuel line going to the engine-driven fuel pump and drained all the fuel from that as well.Next, five gallons of 100LL (donated gratis by the fueling company) was poured into the main tank, pumped through the system using the electric boost pump, and drained from the disconnected fuel line into a five-gallon bucket. The fuel in the bucket was tested for Jet A contamination using the paper-towel test: A few drops are placed on a paper towel and allowed to evaporate completely. Pure 100LL will not leave an oily ring on the towel, but even small amounts of Jet A contamination will leave an obvious ring. The stuff in the bucket flunked the test.Another five gallons of 100LL were poured into the tank, and the process repeated. Once again, it flunked the paper-towel test. We had to repeat the procedure three more times before we were satisfied that the system was essentially kerosene-free. We reconnected the fuel line, cowled-up the engine, the fueling company then topped off the airplane (again gratis), and I was finally good to go … fully six hours after the misfueling incident.
I learned some important lessons that day. Perhaps the most important is that it’s impossible to distinguish pure avgas and a mixture of avgas and Jet A by color alone. My main tanks had been about half-full of avgas, so after the misfueling, they contained roughly a 50-50 mix. If you take a jar full of pure 100LL and another jar full of a 50-50 mix of 100LL and avgas, I guarantee you will not be able to see any difference in color or clarity between the two.I hadn’t realized that before. I had always been taught that you sump the tanks and observe the color — 100LL is blue and Jet A is straw color. What I was not taught is that a mixture of 100LL and Jet A is also blue and that you simply can’t tell the difference visually. In retrospect, I shudder to think what would have happened had I not caught that Jet A truck in front of my airplane.I was also taught that since Jet A is significantly heavier than avgas (6.7 lbs./gal. versus 5.85 lbs./gal.), the Jet A and 100LL will separate just like oil and water, with the Jet A at the bottom (where the sump drain is) and the 100LL at the top. That’s true, but only if the contaminated fuel is allowed to sit for hours and hours. It turns out that 100LL and Jet A mix quite well, and the mixture takes a surprisingly long time to separate.There are at least two good ways to distinguish pure 100LL from kerosene-contaminated 100LL. One is by odor: Jet A has a very distinctive odor that is detectable even in small concentrations. The other (and probably best) is by using the paper-towel test: Pour a sample on a paper towel (or even a sheet of white copy paper), let it evaporate and see if it leaves an oily ring.
What effect does Jet-A contamination have on a piston engine? Enough to ruin your day.You can think of Jet A as being fuel with a zero octane rating. Any piston engine that tries to run on pure Jet A will go into instant destructive detonation. However, in real life, we almost never encounter that situation because the tanks (at least the main tank used for takeoff) is almost never completely dry when the aircraft is misfueled.Therefore, the real-world problem is not running on pure Jet A, but on running on a mixture of 100LL and Jet A. Depending on the mixture-ratio of the two fuels, the effective octane rating can be anything between 0 and 100. A mixture with a lot of Jet A and just a little 100LL might be detectable during runup. A 50-50 mix might not start to detonate until full power is applied, and the engine might fail 30 seconds or three minutes after takeoff. Just a little Jet A contamination might produce only moderate detonation that might not be noticed for hours or even weeks. Like so many other things in aviation, “It all depends.”The Cirrus SR22 accident in Rio reminds us that the problem of misfueling is still with us, despite all the efforts of the FAA to eradicate it. We need to be vigilant. Always watch your airplane being fueled if you possibly can. Make sure its fuel filler ports are equipped with restrictor rings. Don’t just look at the fuel you drain from your sumps — sniff it, and when in doubt, pour it on a paper towel.See you next month.
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