On May 9, two Cessna Citation 550s operated by air-ambulance operator Air Trek lost power—in both jets’ engines—due to fuel contamination by diesel exhaust fluid (DEF). The pilots were able to land safely. 

The jets were both fueled by the FBO at Punta Gorda Airport (PGD) in Florida, which is operated by Charlotte Country Airport Authority. According to a spokeswoman for the airport authority, “The incident was isolated to the operations of one fuel truck, but the fuel itself on the truck had not been (and is not) contaminated. However, the icing-inhibitor injective additive appears to have been cross-contaminated with DEF.”

According to information from AOPA, which was confirmed by the airport authority spokeswoman, one of the Air Trek Citations was flying to Niagara Falls, New York, and landed safely in Savannah, Georgia after the failure of both engines. On its way to Chicago, the other Citation “experienced an engine failure, and landed safely in Louisville, Kentucky,” AOPA said. 

In a preliminary accident report on the Citation that landed at Savannah, the NTSB said that the airplane flew to Naples, Florida after being fueled with 480 gallons of jet-A mixed with a fuel system icing inhibitor (FSII) additive. On the flight from Naples to Niagara Falls, at 35,000 feet and one hour, 20 minutes from takeoff, the left engine slowly started to spool down, and attempts to restore engine power proved futile. After requesting a lower altitude and descending, the pilot shut the left engine down after it showed no oil pressure.

At 8,000 feet while flying to Savannah, the right engine began losing power, and after declaring an emergency, the pilot was able to land on Runway 19. According to the NTSB, "The second-in-command noted that the left fuel filter bypass light did not illuminate but that the right fuel filter bypass light did illuminate."

DEF is required in certain diesel-engine-powered vehicles, typically those built after 2010, including airport fuel trucks. The fluid is indistinguishable from the typical FSII—usually Prist—that turbine engines without fuel preheaters require to prevent fuel icing at high altitudes. DEF is a urea-based solution that lowers nitrogen oxide pollutants in diesel exhaust and is not approved for use in jet fuel. When the two are accidentally mixed, crystals form, causing potentially catastrophic clogs throughout aircraft fuel systems.

Last year, a Falcon 900EX operated by Fair Wind Air Charter suffered failure of two of its three engines after departure from Miami Opa-Locka Airport. Luckily the pilots were able to land back at the airport using the remaining engine. 

Fair Wind COO and equity owner Alex Beringer said that the NBAA DEF task force, of which he is a member, was notified of the Punta Gorda event. “The accidental mixing of DEF into the Prist tank is likely what occurred,” he told AIN. “DEF is a risk and remains a risk as long as these fluids remain on airport property.” 

This is the third recent instance of DEF contamination, with, fortunately, no fatal accidents. Last November, seven turbine-powered aircraft at Omaha’s Eppley Airfield were serviced with jet fuel that had accidentally been treated with DEF. 

DEF Mitigation Efforts

The task force, which includes the FAA, industry groups, ground service operators, fuel providers, and operators, is working on mitigating the threat of DEF at airports. “My recommendation,” said Beringer, “is to get DEF off the airport property and exempt those on the airport property from DEF. That’s the fix for sure. Look at what happened to those two Citations. Luckily we had three motors and we lost only two of them. It’s only a matter of time before something happens and hurts people.”

The problem with DEF stems not only from the requirement that modern diesel-powered trucks require the fluid but that the trucks have to carry DEF tanks and icing-inhibitor tanks. If the fluids get mixed up, it is nearly impossible to tell them apart.

In the case of Fair Wind’s Falcon, the FBO had a good system, Beringer said, “but it fell apart.” There was no DEF stored at that facility, to help prevent accidental mis-filling. But the icing-inhibitor tank needed to be repaired, so a mechanic removed and welded the tank, then before reinstalling it back on the truck filled the tank with DEF instead of Prist.

After the incident, Beringer wrote to the Environmental Protection Agency, senators, members of Congress, the FAA, and the Department of Transportation. The bottom line is that states regulate the requirement for DEF, he explained. Lacking an effort to convince every U.S. state to exempt airport vehicles from the DEF requirement, a national regulation would be helpful, he said. “Until then FBOs have to get on top of their DEF policies. Until airport service vehicles are DEF-exempt and the DEF systems are not installed [on airport fuel trucks], there is a risk that requires mitigation, training, and auditing. The pilot is the last line of defense. It’s a big deal. I cannot stress how much of a problem this is.”

Beringer recommends that pilots who fly airplanes requiring icing inhibitor verify what is in the tank that is being mixed with their fuel, how that tank was serviced, and what safety precautions were taken to ensure that the proper fluid is added. 

“We keep getting lucky with these events,” he said, “and we haven’t killed anybody, yet. It’s just a matter of time.”

For its part, the Charlotte Country Airport Authority can’t provide details of how the two Air Trek Citations were contaminated, due to “an ongoing FAA investigation,” according to the spokeswoman. However, she told AIN, “The Charlotte County Airport Authority is working cooperatively with the FAA to ensure it has all the support and information they need. We have brought in a third party to review our procedures and make further recommendations.”

The airport authority’s fueling operation uses NATA’s Safety 1st training program; supervisors have all completed the supervisor-level training, while staff members all undergo Safety 1st PLST. The operation is also ACE certified by fuel supplier Eastern Aviation Fuels, with four supervisors certified in the ACE fuel quality control training program. As of now, the Airport Authority does not participate in a safety management system.

The airport authority’s fuel truck fleet includes two 1999 models that don’t need DEF and three trucks (one 2015 and one 2018) that require DEF. “Absolutely we support [exempting airport fuel trucks from the DEF mandate],” the spokeswoman said. 

Although it can’t comment in detail about how the DEF incident happened, she added, “We have isolated the issue, however, we’re reviewing all procedures to provide a comprehensive fix.”

The NTSB's report on the Air Trek Citation that landed in Savannah included these details about how the fuel was contaminated: 

"According to a lineman who worked for the fixed based operator at PGD, the evening before the incident, he noticed that the FSII was low on a fuel truck and he intended to refill it. He went to a shed where the FSII was located and noted that the FSII bottle was partially filled, and that there was another bottle next to it that was partially filled. He combined the two bottles and then refilled the fuel truck FSII reservoir. Several days after the incident, the lineman realized that he had inadvertently combined a 5-gallon FSII bucket and a 2.5-gallon diesel exhaust fluid (DEF) container instead of two partially-empty containers of FSII.

"Fuel samples, fuel system filters, and fuel screens from the airplane were obtained and sent for laboratory testing. Analysis of the fuel contaminants indicated the presence of urea, the primary chemical found in DEF."

According to NATA president Gary Dempsey, “DEF contamination is a serious safety concern. NATA is monitoring the issue and assisting with initiatives like participating in a working group comprised of government and industry stakeholders tasked with developing resources to mitigate DEF contamination incidents at airports.”

Air Trek released a statement about the engine-failures in its two Citations:

“Air Trek is extremely proud of the extraordinary professionalism of our pilots and medical team. Air Trek’s pilots are heroes of the day,” said Dana Carr, v-p and director of operations. “Air Trek has worked closely with [Punta Gorda] staff for 41 years. The [Punta Gorda] fueling meets standards of the NATA Safety 1st program and [the airport authority] is confident this is an isolated incident. Air Trek defers commenting on details related to the incident due to the ongoing investigation.”