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Misfueled!

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Jet fuel contamination of avgas remains a killer.

On March 2, 2008, a turbonormalized Cirrus SR22 was destroyed when it crashed shortly after takeoff in Rio de Janiero, 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 SFO. 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 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.”

Theoretically impossible

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 by 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 indicents and accidents were occuring in turbocharged aircraft. These aircraft typically were prominentaly 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 said 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.)

Jet-A nozzle vs. avgas nozzle

Jet fuel nozzles have a wide spade top that is theoretically incapable of being inserted in an avgas fuel filler equipped with a restrictor ring—but don’t count on it!

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 overitself 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 manger 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, 5 gallons of 100LL (donated gratis by the fueling company) was poured into the main tank, and then pumped through the system using the electric boost pump and drained from the disconnected fuel line into a 5-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 5 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 kerosine-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.

Restrictor filler & GATS jar

Be sure all your fuel filler ports have restrictor rings. The big GATS jar (available at Sportys, Aircraft Spruce, and elsewhere) does a far better job than the slim screwdriver-type testers.

Lessons learned

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 has 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 kerosine-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.

Nasty stuff

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 3 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.

Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 8,000-hour pilot and CFI, an aircraft owner for 50 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviation. Mike writes a monthly Savvy Maintenance column in AOPA PILOT magazine, and his book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions (112 pages). His second book titled Mike Busch on Engines was released on May 15, 2018, and is available from Amazon.com in paperback and Kindle versions. (508 pages).

6 Comments

  1. I did some cursory research a year or so ago and could not find anything that mandates the change-over of Jet A nozzles to the so-called Hoover nozzle, i.e., the spade-shaped nozzle that won’t fit in a standard avgas filler port. In other words, the airplanes may have the requirement; the fuel suppliers don’t. My research wasn’t complete by any means, but it emphasized to me that even those of us who drive simpler non-turbocharged piston singles need to watch the refueling process, to insure that the right stuff is pumped.

    Incidentally, the “Hoover nozzle” is named because it came into being after Bob Hoover’s Shrike was misfueled with Jet A, he suffered a pair of total engine failures at low altitude, but because of his skill, he and his passengers survived the subsequent crash landing.

    Another and equally good reason to watch the refueling process is to make sure it’s complete. “Complete” means that if the request was “top it off”, make sure that happened, and then make sure that the cap is properly secured. In this day of fuel flow monitors/totalizers, with many built in to glass panels, they can’t be accurate unless indeed they reflect the actual fuel on board, and they won’t be accurate at all if fuel is siphoned overboard because a cap disappeared enroute. Depending on the design of the fuel tank, the dihedral of the wing, and how careful the refueler is, it’s possible for a pilot to think a wing tank is full when it’s actually several gallons low. In 4 decades of flying small planes, not only have I had many refuelers not fully fill the airplane’s tanks, I’ve had at least half a dozen refuelers fail to properly secure the fuel caps.

  2. Great story. Mistakes happen. The point is to catch them before they get worse, and keep your cool so you can judge whether the plane is still airworthy. Then, pass on the experience to others so we all can learn from it!

  3. I recently saw a summary of several misfueling incidents that raised a critical point: in every case, the fuel receipt was accurate, reflecting the fuel that was actually put into the aircraft. It might be good to be in the habit of reading your receipt before starting up.

  4. Back in the 60’s I was a refueling dispatcher in the Airforce and one night we were really busy. The truck drivers were out on the line a long time and there were not enough night shift to relieve all the day shift. The trucks had big, big letters showing the type of fuel in them but one truck pulled up to the wrong fuel pit to refill. Neither the driver nor the pump house operator noticed the big letters on the side of the truck and the truck got filled with 4,000 gallons of the wrong fuel. The truck then went to service another aircraft. No damage was done due to an awake crew chief but the possibilities were great. I don’t know what precautions are taken now but the wrong fuel in the right truck is disaster.

    • Figured I’d share but I’m in POL now! So the Air Force converted fully to Jet A and solely puts the fuel in the R-11 tankers (6,000 gal). AVGAS, MOGAS, Diesel, etc go in the C-300 fuel trucks. Also now each truck has a fuel grade specific computer on board that must be physically connected to the fill stand (same as many civilian trucks) that will not let the wrong product enter the truck.

  5. One thing a lot of people don’t realize is that the GATS jar can tell if there is a mixture of Jet A in the tanks. When the fuel is poured back in to the tank through the screen and allowed to evaporate, the number of holes in the screen that don’t evaporate i.e. 10% will tell you that you have a 10% mixture of Jet A.

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