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In the wake of several incidents involving the contamination of jet fuel with diesel exhaust fluid (DEF), the National Transportation Safety Board (NTSB) is highlighting the dangers of such contamination with the release this week of a new safety alert (SA-079) and an accompanying poster. The safety alert warns jet fuel providers to take measures to prevent the possible contamination of DEF into jet fuel.
Required for all new on- and off-road diesel-powered vehicles, DEF is becoming more prevalent on airfields as refueling trucks are replaced, NTSB advised. The urea-based clear, colorless DEF reduces nitrogen oxide (NOx) emissions when injected into the diesel-powered vehicle’s exhaust stream, NTSB said.
However, the Safety Board added, “DEF is not designed, nor approved, for use in jet fuel. If it is inadvertently added to jet fuel, as has happened in several incidents over the last two years, DEF will react with certain chemical components to form crystalline deposits in the fuel system. The crystalline deposits can then accumulate on filters, engine fuel nozzles, and fuel metering components and result in a loss of engine power.”
Improperly stored in an unmarked container, DEF can be mistaken for other liquids such as fuel system icing inhibitors (FSII). Both DEF and FSII can be bought in bulk and transferred into smaller containers, increasing the chance of mixing them up.
“The NTSB wants fuel providers to ensure they store all chemicals in labeled containers and that they add a ‘NOT FOR AVIATION USE’ label to all DEF containers,” the safety agency added.
The most recent cases of such contamination involved two Cessna Citation 550s operated by air ambulance provider Air Trek that lost engine power in May. The crews diverted and safely landed. In this case, an airport lineman reported that prior to the incidents, he had combined two partially filled containers, one with the FSII and the other DEF, which he had mistaken for FSII. He added the combined fluid into the fuel truck’s FSII reservoir. Detailing the investigation of one of the Citations, NTSB said it had been filled the next day with 480 gallons of Jet A fuel with FSII additive mixed at the time of fueling. “Analysis of fuel samples, fuel system filters, and fuel screens from the airplane indicated the presence of urea, the primary chemical found in DEF,” NTSB said.
NTSB pointed to other incidents involving the introduction of DEF into aircraft fuel tanks, including cases in November 2017 in Omaha, Nebraska, and in August 2018 in Miami that led to the exposure of DEF to a combined 27 aircraft. DEF was directly injected into 12 of those aircraft, all of which experienced service difficulties and were forced to divert. They had clogged fuel filters and fuel nozzle deposits.
The Safety Board outlined a series of measures that can be taken to avoid such contamination, including:
- Avoid use of temporary containers; rather use containers and labels that meet OSHA requirements;
- Ensure that all containers are clearly marked with four-inch or larger letters visible from all sides, with the markings of “DIESEL EXHAUST FLUID (DEF)” or “JET FUEL SYSTEM ICING INHIBITOR;”
- Add a label to all DEF containers that says, “NOT FOR AVIATION USE;”
- Ensure DEF and FSII containers are not stored near each other, even if carefully marked;
- Train all staff on storage locations, packaging, and labeling of DEF and FSII, as well as the hazards of contamination;
- Discard any jet fuel or FSII suspected of contamination;
- And, review the recently released Aircraft Diesel Exhaust Fluid Contamination Working Group Report.