Recent incidents involving diesel exhaust fluid (DEF) contamination underscore the “very real threat” such events pose and the need for increased training, the National Air Transportation Association said.

The latest contamination occurred earlier this month, resulting in loss of power in the engines of two Cessna Citation 550s. An FBO at Punta Gorda Airport in Florida had fueled the aircraft. Officials believe that an icing-inhibitor injective additive had possibly been cross-contaminated with DEF.

This was the third time in less than two years such an event has occurred, NATA noted, adding in all three cases multiple inflight engine failures occurred with possible significant damage to the fuel systems and engines.

After a 2017 contamination incident, NATA created a free DEF Contamination Prevention training course. “This most recent incident, however, highlights yet again, just how serious the DEF contamination risk is, and how it is still a very real threat,” the association said. “FBOs and aircraft operators must be diligent in ensuring that staffs are not only properly trained, but that company policies and procedures used to prevent DEF contamination are being followed.”

While a review of the most recent contamination is still ongoing, the earlier incidents involved an inadvertent addition of DEF into the fuel truck’s fuel system icing inhibitor (FSII) storage tank and then injected into the fuel.

DEF, a clear liquid, is used to reduce emissions of modern diesel engines, but is designed for use only in vehicles produced since 2010 and equipped with selective catalytic reduction systems. When combined with jet fuel, NATA said, DEF forms crystalline deposits in the fuel system. This puts the aircraft at risk for an in-flight engine failure.

NATA encouraged fuel providers to read the FAA’s guidance on the inadvertent use of DEF instead of FSII and undergo training for safe handling. NATA’s training course recommends storing DEF and FSII in separate, locked locations using separately marked keys. Staff members should be trained on their locations and differences between packaging and labeling, while only trained personnel should handle DEF, it said.