DEF Contamination Causes Dead-Stick Landing, No Injuries


Despite a major awareness and training campaign, the National Air Transportation Association says diesel exhaust fluid (DEF) remains a potentially catastrophic hazard for aviation. In a news release, the organization said a business jet in the southeastern U.S. recently experienced a double flameout and glided to a dead stick landing 280 miles away. There were no injuries but the report didn’t say if the aircraft was damaged. It was the fifth such incident in five years and so far there have been no injuries, but aircraft engines and fuel systems were damaged.

DEF is not a fuel additive. Its use is mandated for diesel vehicle engines (including those in airport fuel trucks) where it is stored in a separate tank and injected into the exhaust to reduce emissions. When added to fuel, it forms crystals that quickly clog lines and filters and damage moving parts. In the previous cases, DEF was mistaken for fuel system icing inhibitor and added by the FBO. Both are clear fluids. It’s not clear if that’s what happened in the most recent mishap, but NATA is urging fuel handlers to ensure staff training on preventing this kind of contamination.

Russ Niles
Russ Niles is Editor-in-Chief of AVweb. He has been a pilot for 30 years and joined AVweb 22 years ago. He and his wife Marni live in southern British Columbia where they also operate a small winery.

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  1. If the FAA doesn’t get off their behind and exercise their exclusive aviation jurisdiction and eliminate DEF use on fueling trucks, there will be an eventual accident that involves fatalities. I’m surprised the NTSB hasn’t said anything about this as well. This issue would make a perfect hazard report for those with SMS. I wonder what the NTSB’s response to this would be.

    • Unfortunately I don’t think the FAA will be able to pass any rulings over the EPA, which is who requires the DEF solution to emissions. Not directly, but by their emissions standards. And if the FAA did force an exception for the fuelers, I’m not sure where you’d source an engine for a new fuel truck. All the manufacturers make are compliant engines now. Maybe an overseas market engine? Its a sticky wicket for sure. I know one of our local airports just bought a gas engine JET A truck just to avoid DEF.

      • Just asking….does the EPA have jurisdiction over the emissions of a non-roadable, non-registered airport (or farm) truck? Our truck is not tagged, nor registered. It never leaves the ramp.

        • The answer, I think, is yes. Diesel farm tractors are required to use DEF and I’m sure construction equipment too. There used to be a large aftermarket for deleting required diesel emission equipment (including DEF) from vehicles (mostly pickup trucks). These were sold as “for off road use only”. The EPA has ruled that it does not matter if is for “off road”, it is illegal to remove the equipment from vehicles that were certified with it. The EPA has fined and shut down lots of these businesses.

    • An easy solution to getting rid of DEF — switch to electric trucks. They do not go far or fast anyway and it would save money on fuel and maintenance.

      • Saving money on fuel is largely going to be a wash, I think. I hereby refer you to the growing body of evidence that it costs just as much or more to charge electric cars as it does to fuel gasoline cars. And keep in mind that this will get worse as there is more and more demand for electricity, and that it will probably get worse again as more and more of the available electricity is mandated to be produced by less efficient and more reliable “green” methods.

        Then, consider that the electric vehicles will cost more than the gas ones they are replacing to purchase. And then consider that the battery packs, when they inevitably fail, may not be cost effective to replace, and will cost far more than a few oil changes over those same years would have cost. Oh, and don’t forget that EV tires are more costly than tires for IC vehicles due to the extra weight of EVs.

        Basically, I’m not sure there is as much savings there as you might assume, if everything is properly accounted for. I personally think it would be far more effective to simply stop mandating costly “solutions”that seem to cause more problems than they solve, DEF included.

        • I don’t know what growing body of evidence you have, but we replaced my wife’s car (Chrysler 300) with a Tesla. I used to spend about $250 per month in gas for her daily commute. The Tesla only increased our home electric bill by about $70 per month. The electric car is definitely cheaper to operate than the gas car was. No, it’s not free. Yes, it costs far less.

  2. dan@ninjacowfarm has the present solution. Here is a case where electric might be worthwhile, all low speed short distance.

  3. Another case of mistaken fueling. Not paying attention and not reading placards. Simple as that. We cannot fix stupid.

    • How many turbo charged piston airplanes are in debris after being fueled with Jet-A thank to “Stimpy” the new lineman? Maybe they could color one of the fluids, since both are clear.

    • One of the reasons the FAA years ago mandated jet fuel dispensers have a wide nozzle so that it could not be dispensed in avgas powered planes that the FAA also mandated modifications to narrow the fuel entry points on those avgas fuel tanks.

  4. there were two jets flown out of opa locka…one landed with one engine out, the other landed with both engines out. the third was an Eclipse that got the word and did not fly but it was totaled due to fuel system crystalization.

    • They cannot mandate that. I’ve known the FAA to get off their ass many a time. Keyboard Cowboy Kent you do not help the matter.

  5. This is an informative article, and I didn’t realize DEF was carried on the fuel trucks. I think something is amiss, though, in the remark that the jet “experienced a double flameout and glided to a dead stick landing 280 miles away.” Assuming the flameout occurred at the highest possible altitude of 52,000′ (~10sm), that means the glide ratio was 28:1. If the glide was 280nm, the ratio was even higher. I don’t have any jet time and certainly no deadstick jet time, but do have some glider time (in Grob sailplanes) and of course simulated and even actual engine out time from flight training. 28:1 just seems high to me. I’d be interested in knowing if that’s possible in a smaller jet.

    • DEF isn’t carried on fuel trucks but ice inhibitor fluid is. The problem is that the ice inhibitor fluid is refilled from bulk containers. DEF is also stored on site in bulk containers. More than likely the ice inhibitor supply on the fuel truck was filled incorrectly from the DEF bulk container. It seems obvious that these two fluids should not be stored anywhere near each other.

      • DEF is carried in fuel trucks. I always supervise fueling of my airplane and I have seen DEF tanks along with Prist tanks on the same truck. Fortunately the plane I fly doesn’t need Prist. It would be easy to put the wrong chemical additive in the wrong tank. The FAA needs to ban DEF equipped fuel trucks from airports before someone gets killed because of an engine failure.

        • Interesting. Into what does an airport fuel truck dispense DEF? Assuming no aircraft requires DEF, I’m surprised that the truck would carry DEF around. It may have a supply on board for the fuel truck itself to use.

          • As far as I know aviation fuel trucks don’t dispense DEF. It still has a tank marked DEF that the truck uses. I think the only reason an airliner has not had any DEF added by mistake is that those planes don’t need Prist added to their fuel supply. I’ll bet if an airliner did have an engine quit because of DEF added by mistake, the bureaucrats at the FAA would act.

    • I can’t confirm the glide ratio mentioned but you would be amazed how far some jets do glide. I think that is the reason so many pilots get themselves in trouble with runway overshoots and excursions. It is also the reason jets have speed brakes ( the British call them air brakes). Since jets don’t slow down as fast as a prop plane they have the extra drag devices to help slow down when needed.

  6. Fueling folks really need to know about airplanes and how to service them. Training properly might help.

  7. DEF:
    Copied from Cummins:
    Small quantities of diesel exhaust fluid (DEF) are injected into the exhaust upstream of a catalyst, where it vaporizes and decomposes to form ammonia and carbon dioxide. The ammonia (NH3) is the desired product which in conjunction to the SCR catalyst, converts the NOx to harmless nitrogen (N2) and water (H2O).

    In our world of aviation a mistake made by some tired, end of shift, line person is deadly. Perhaps the NTSB could splain to the EPA the deadly hazard?

    Seems to me: DEF exhaust systems could be removed from a diesel powered fuel truck and revert to non-DEF operation. Wouldn’t need to replace the entire engine. Ditch the DEF exhaust system and revise engine computer programing.

    DEF has also been an expensive pain in the a$$ even in the world of trucking.
    Copied from
    Common issues surrounding diesel exhaust fluid (DEF) are inadvertently putting DEF into the diesel tank, DEF contamination and improper handling of DEF. Every day, technical support teams at construction equipment manufacturers and dealers get calls from customers covering any number of topics.

    Tom C.

  8. I agree with Karrpilot – you can’t fix stupid. Every DEF container that I’ve seen is clearly marked as such. Many users don’t even know that it stands for Diesel Exhaust Fluid, but every owner knows what DEF is. Synonymous with PIA. Ask any operator that has to pull over while the system regenerates. It began in 2008, much wider use in 2010, so even “older” engines are using it. Cummins says the fuel-to-DEF usage is about 50:1, so most fuel trucks won’t use a huge amount. That being said, at any airport with diesel-powered equipment, DEF should be stored in a separate, secured area, accessible by only trained and responsible individuals (read: The very few). And as the sales of DEF compared to de-icing chemicals is probably millions to one, have the de-icing containers changed in labeling/container shape/both to help prevent further incidents. But again, you can’t make anything idiot-proof, because when you think you have, along comes a better idiot.

    • DEF does not require a regeneration cycle. You may be thinking of the Diesel Particulate Filter (DPF) which periodically goes through a regeneration cycle to burn off the accumulated soot. This does not require you to “pull over”. In fact, the regeneration process works much better at highway speeds as it depends on a hot running engine.

  9. Can a coloring agent be added to the DEF just as diesel fuel that’s dyed red cannot be used in vehicles meant for public roads?

    • No, That has been tried and any dyes added were detrimental to the chemical reaction. All DEF is about 68% deionized water.

      SCR is going to get mandated for off road and marine applications. It is not going away. It i a cheap fix for the engine manufacturers and they profit handsomely for their clap trap SCR systems the end user ends up having to maintain.

  10. Um, so if diesel exhaust is so bad, what about diesel aircraft engines? There is a Part 141 school at my home airport that has a fleet of aircraft with diesel engines.

      • So what – there is really very little difference in Jet A Kerosene and the modern ULSD – Ultra Low Sulfer diesel. If Jet A was so much more cleaner to operate it would have been used as a primary fuel for the on road emissions solution. The only reason you do not need emissions reduction on the Jet A turbine and piston aircraft is the same FAA that everyone is complaining about.

        • There is quite a bit of difference between the two. And we work on lowering emissions all the time (I’m in jet engine certification.) The best way, of course, is to increase efficiency.

  11. This misguided push for clean emissions applied to ramp vehicles is probably going to get somebody killed before its all said and done.

  12. DEF just as Ethanol are solutions that cause more serious problems than the ones they were meant to mitigate.

    • So what do you do to prevent pollution? Because people will do things, companies will do things. I grew up in a very polluted area; the EPA’s regulations fixed that.

  13. Interesting read: 2019-08-30_Safety_Risk_Assessment_Report_DEF-Final.pdf
    From the FAA dating back to 2019 : Risk Assessment Report.

    Summary of Safety Issue: Between November 2017 and May 2019, there were three events
    of jet fuel contamination with diesel exhaust fluid (DEF). DEF is not a fuel additive; it is required
    by the Environmental Protection Agency (EPA) to be used on diesel trucks to reduce nitrogen
    oxide (NOx) emissions.

    Safety Recommendation Responsible Organization
    1. Update Advisory Circular (AC) 150/5230-4B to
    incorporate fuel additive training, to include DEF and
    FSII handling.
    2. Communicate risk level of jet fuel contamination with
    DEF to the EPA. AVS-1
    3. Request the EPA to issue permanent relief from
    emission control/system performance inducements
    (which require the use of DEF) for any non-road
    compression engine powered vehicles operating at/on
    4. Engage with National Association of State Aviation
    Officials (NASAO) on the risk of DEF to airports not
    certificated under Part 139 or receiving funds through
    the National Plan of Integrated Airport Systems
    5. Investigate adding dye to DEF to distinguish it from FSII
    or adding dye to FSII to distinguish it from DEF. AIR-20
    6. Investigate the creation of a required inspection item
    regarding DEF in the Program Tracking and Reporting
    Subsystem (PTRS) and Safety Assurance System