The NTSB has issued a Safety Alert asking jet fuel providers to take measures to prevent fuel contamination by diesel exhaust fluid (DEF). The board warned that the addition of DEF to jet fuel can cause a chemical reaction that forms crystalline deposits in the fuel system, increasing the risk of engine failure due to deposit accumulation on filters, engine fuel nozzles and fuel metering components.
DEF is a clear, colorless liquid commonly added to the emissions systems of ground vehicles, including airport refueling trucks, to reduce nitrogen oxide (NOx) emissions. “DEF can be mistaken for other clear, colorless liquids, such as fuel system icing inhibitors (FSII),” the NTSB said in the Safety Alert (PDF). “Both products can be purchased in bulk and transferred to smaller containers for ease of use. Both are usually stored in milky white containers. Also, airport refueling trucks are serviced with both products.”
According to the NTSB, it is aware of two incidents in which DEF-contaminated fuel has been distributed to aircraft. The first occurred in November 2017 at Eppley Airfield (OMA) in Omaha, Nebraska, and the second in August 2018 at Miami-Opa Locka Executive Airport (OPF) in Opa-locka, Florida. Both incidents were the result of “inadvertent introduction of DEF into aircraft fuel tanks by way of a refueling truck FSII reservoir.” The board is also investigating a May 2019 incident involving a Cessna C550 that experienced a total loss of engine power to both engines likely related to DEF-contaminated fuel.
The NTSB says jet fuel providers should take measures to avoid putting chemicals into unlabeled containers, ensure containers are marked with 4-inch or larger stenciled letters visible from all sides, label DEF containers “NOT FOR AVIATION USE” and avoid storing DEF and FSII close to each other. The NTSB also suggested training staff on DEF contamination hazards, storage locations and labeling practices and asked that operators ensure any fuel or FSII suspected of DEF contamination be discarded.