Concerned about the “major” safety risk associated with potential diesel exhaust fluid (DEF) contamination in turbine aircraft, a government-industry safety evaluation team is recommending that the Environmental Protection Agency (EPA) exempt airport vehicles from mandatory use of the additive. The recommendation was among 15 that the FAA Safety Risk Management Team (SRM) developed after evaluating risks associated with on-airport DEF use.

Recommendations also surrounded training for DEF handling, communicating the associated risks, exploring the potential of dyes for identification of the additive, reaching out to manufacturers and suppliers on the potential damage, conducting further research of the reactions involved with DEF, and updating guidance and other safety information, among other suggestions.

The SRM, which comprised cross-section of FAA and industry representatives, was established following three events of jet fuel contamination with DEF. Since 2010, the EPA has required on-road diesel trucks to use DEF to reduce NOx emissions. That requirement expanded to other diesel trucks, including airport vehicles, in 2014. But when mixed with jet fuel, DEF clogs jet engines' fuel filters and nozzles, causing engine damage and in-flight shutdowns.

In each of the three events, FBO personnel inadvertently added DEF to fuel truck anti-icing injection (FSII) system reservoirs. Collectively 18 aircraft—including three military airplanes—were fueled with the contaminated fuel. As a result, six civilian and three military aircraft were forced to perform emergency landings.

The SRM concluded that contamination poses a high risk to both commercial and general aviation aircraft and identified several causes for such events.

While noting that a root cause is the EPA mandate itself, which has led to the increased use of DEF on airports, the SRM pointed to “confusion in the identification and differences between DEF and FSII by fueling personnel.” It added, “There are varying applications of training and inadequate awareness regarding the dangers of jet fuel contamination with DEF.” The team further cited inconsistent adoption of industry-wide standards and guidance, as well as gaps in regulatory oversight.

“The presence of DEF on airports creates the hazard of jet fuel being contaminated by DEF,” the report states. “The hazard primarily applies to Part 91 and 135 operations. Any refueling trucks with FSII containers have the potential to be contaminated with DEF, and any aircraft that requires FSII also has the potential to be contaminated with DEF.

Such a request for an exemption would come from industry. But many of the other initiatives are more collaborative and already underway. The FAA and industry have sounded the alarm in the general public about the risk, and NATA has issued decals to clearly identify DEF containers. Research on the possibilities of dyes is ongoing, as are discussions of using different-size containers or premixed fuels with FSII.