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Urgent: Isolate DEF Additive from Operations

The FBO industry should be on alert for accidental Jet A fuel contamination from the misuse of diesel exhaust fluid (DEF).

We can all learn from a recent aircraft incident involving an aircraft that was forced to make an emergency landing after experiencing engine problems. The culprit turned out to be fuel contamination from DEF, an additive used to lower diesel engine exhaust emissions, which was accidentally introduced into the fuel by an FBO refueling the aircraft.

According to reports, the DEF contamination came from a refueler-mounted tank used to dispense fuel system icing inhibitor (FSII), which is sometimes referred to as Fizzy and includes products such as PRIST and Di-EGME.

Because many FBOs have diesel-powered GSE, particularly refuelers manufactured after 2009, they have DEF on the premises. DEF and FSII products are often stored near each other and may confuse employees because both products are clear and dispensed from similar containers, usually 55-gal. barrels.

DEF and FSII products are not interchangeable. If DEF is mixed with Jet A fuel, it will start to thicken or crystallize when an aircraft reaches cooler altitudes. The result can be catastrophic. Fuel lines can clog, and engine shutdown is possible. The cost to repair an aircraft after DEF contamination can be significant.

Best Practice

As a best practice, we strongly recommend that you immediately separate the storage of DEF from your FSII products as well as other fluids, chemicals and lubricants. We also suggest you place a lock on the storage area where you keep the DEF and restrict access to only supervisors and managers.

In addition, we recommend that you develop a standard operating procedure (SOP) for the handling and storage of DEF. Add this procedure to your SOP manual, and conduct appropriate training of your personnel.

As a guide, here are some best practice ideas sparked by NATA’s Safety 1st Program:

  1. FSII should be stored in a separate location from DEF and other fluids
  2. Only trained and approved personnel should handle DEF
  3. Record training in employee records
  4. Training should include the location of DEF and FSII and packaging and labeling differences
  5. Keep a log of all FSII transfers from storage to refueling equipment

We also suggest that employees be trained to be vigilant about possible fuel contamination. If in doubt, the employee should not proceed and report any concerns about possible fuel contamination to a supervisor.

Free Training Available from NATA

NATA Safety 1st has created a DEF Contamination Prevention course available to anyone in the industry free of charge. Current Safety 1st users have the ability to assign the course to their employees in their Safety 1st training accounts. (Click here for help on assigning a course.) Companies that are not current Safety 1st users should contact for complimentary access to the DEF Contamination Prevention course.

Please leave any comments you have about this blog post below. If you have any questions, please give us a call or send us an email:, 404-867-5518;, 972-979-6566.


John Enticknap has more than 35 years of aviation fueling and FBO services industry experience and is an IS-BAH Accredited auditor. Ron Jackson is co-founder of Aviation Business Strategies Group and president of The Jackson Group, a PR agency specializing in FBO marketing and customer service training. Visit the biography page or for more background.


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