Diesel Exhaust Fluid (DEF) Contamination Prevention

What is Diesel Exhaust Fluid (DEF)?

DEF is an aqueous solution containing 32.5% automotive grade Urea in de-ionized (purified) water. It is not toxic, not hazardous and it has no color. This last characteristic is really important to understand why DEF contamination occurs. DEF is not a fuel additive. In fact, it is stored in a separate tank on vehicles with an SCR system.

DEF use in aviation

DEF is mixed with diesel or jet fuel, crystalline deposits are formed in the fuel. These deposits can clog fuel filters, fuel system components and corrode materials and be potentially catastrophic.

Three examples of DEF contamination

Eppley Airfield (OMA) DEF Contamination Event

On November 18, 2017 an operator noticed a discrepancy. It appeared that the FSII container of a truck was accidentally filled, the day before, with 3.5 gallons of DEF. After several quality check controls on fuel trucks and farm, tests came back clean and the trucks were returned to service. On November 19, 2017, the FSII container was removed from the truck and replaced with a fresh undiluted FSII container. But, on November 20, 2017, another operator noticed again a discrepancy with the fuel. In fact, the FSII container, removed from the first truck, was 1/3 full with 60% DEF and installed on another truck. So, all the fuel was removed from the trucks and replaced with a clean fuel. All FSII containers were emptied and refilled with clean FSII on November 27, 2017. On November 30, 2017 the FBO was advised by the supplier that urea was found in a fuel sample but the source of the contamination was unknown. Then, the FBO started to identify and notify all operators fueled between November 17 and November 21.

In total, 13 aircraft and were contaminated with DEF either with contaminated fuel or fuel using equipment exposed to DEF.

Miami-Opa Locka Executive Airport (OPF) DEF Contamination Event

On August 14, 2018, the flight crew of a Dassault Falcon 900EX was forced to returned to OPF after several clogged fuel filter warnings and an engine failure on departure. While returning to OPF, a second engine became unresponsive to throttle inputs. Investigation showed there was a DEF contamination due to a FSII tank that had been removed from a fuel truck for repair and then accidentally filled with DEF to check the presence of leaks. To avoid cross-contamination, procedures had been provided, but they were based on the fact that the tank was kept on the truck.

In total, 14 aircraft were contaminated with DEF either with contaminated fuel or fuel using equipment exposed to DEF.

Punta Gorda (PGD)

On May 9, 2019 two Citation 550s experienced an engine flameout. Both aircraft were fueled at Punta Gorda Airport (PGD) and flew to Naples Airport (APF). Once arrived at APF, both were refueled. The first aircraft was headed to Chicago Executive Airport (PWK) when it experienced, at 35,000 feet, an engine flameout. While descending on approach to Savannah/Hilton Head Airport (SAV), it experienced a second engine flameout at 8,000 feet. Thankfully, it landed safely. The second aircraft was headed to Niagara Falls International Airport (IAG) when it experienced at, 36,000 feet, an engine flameout. Finally, it landed safely at Louisville International Airport (SDF) with one operative engine. It was confirmed that there was no contamination. But, investigation are still in progress as:

– It appeared a pail of unmarked DEF was mixed with a container of FSII.

– An Eclipse jet was fueled the same morning with FSII from the same truck and hadn’t experienced any problems.

It is highly recommended that all Fixed Based Operator (FBO) staff receive general Diesel Exhaust Fluid (DEF) Contamination Awareness training.