Ongoing DEF Fuel Contamination Problem Sparks Safety Alert from NTSB
Wednesday, July 31, 2019 at 3:12PM
John L. Enticknap and Ron R. Jackson, ABSG in DEF, DEF Contamination Prevention, FBO Best Practices, FBO Best Practices, FSII, NATA, diesel exhaust fluid, fuel system icing inhibitor

After several incidents involving diesel exhaust fluid contamination of jet fuel, the National Transportation Safety Board has issued a Safety Alert and has created this poster. We recommend hanging it in the line service area of your FBO as well as chemical, fluid and lubricant storage locations. Courtesy: NTSB.In response to several incidents within a 19-month period, last week the National Transportation Safety Board (NTSB) issued a Safety Alert warning providers of jet fuel to take measures to prevent diesel exhaust fluid (DEF) contamination.

In a related news release, the Safety Board says it wants fuel providers to keep all chemicals in labeled containers and to add a label to all DEF containers that reads, “NOT FOR AVIATION USE.”

We also recommend that FBOs use this NTSB poster in their operations. Post it in the line service area as well as where any chemical, fluid or lubricant is stored.

More Recent Developments

The latest DEF contamination incident took place on May 9. Two Cessna Citation 550s lost power in both engines after being refueled at the same FBO.

A month later, the National Air Transportation Association (NATA) and other organizations issued “A Collaborative Industry Report on the Hazard of Diesel Exhaust Fluid Contamination of Aircraft Fuel.”

In August 2018, we urged FBOs to isolate DEF in their fueling operations, and we cannot stress enough the serious issue of maintaining clean and dry fuel for all aircraft. The industry has been very fortunate that these contamination incidents have not caused injuries or fatalities. FBOs must take concerted action immediately.

The following information reflects an update from our previous blog post on DEF contamination:

Because many FBOs have diesel-powered ground support equipment, particularly refuelers manufactured after 2009, they have DEF on the premises. DEF and fuel system icing inhibitor (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.


As a guide, here are some best practices ideas sparked by NATA’s Safety 1st program as well as the NTSB Safety Alert:

Eight Best Practices to Prevent Diesel Exhaust Fluid (DEF) Contamination of Jet Fuel
1. FSII should be stored in a separate location from DEF and other fluids.
2. Label DEF as “Not for Aviation Use.”
3. All chemicals, fluids and additives should be clearly labeled.
4. Only trained and approved personnel should handle DEF.
5. Train all personnel on the use of DEF, and record training in employee records. Recurrent training should be done, at a minimum, on an annual basis.
6. Training should include the location of DEF and FSII and packaging and labeling differences.
7. Keep a log of all FSII transfers from storage to refueling equipment.
8. Post the new NTSB poster/flyer in the line service area as well as where chemicals, fluids and lubricants are stored.


As a best practice, we strongly recommend that you immediately label all chemicals stored within your operation. DEF should be labeled, “Not for Aviation Use,” and isolated from other chemicals, fluids 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. A use log should be updated anytime the DEF storage area is accessed.

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.

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.

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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