WPR23LA167

The fueler’s inadvertent addition of diesel exhaust fluid (DEF) to the FSII reservoir on the fuel truck, and its subsequent mixture with the JET A that was used to fuel the airplane, resulting in a total loss of power to the right engine and a partial loss of power to the left engine.

The flight crew requested the airplane be topped off with fuel that included a fuel system icing inhibitor additive (FSII/PRIST). The fixed-base operator serviced the airplane with 674 gallons of Jet A and FSII that had inadvertently been mixed with diesel exhaust fluid (DEF). The airplane then departed on a repositioning flight. About 30 minutes after departure, while level at flight level (FL) 350, the captain observed erratic temperature indications on the left engine inlet turbine temperature (ITT) gauge. The right engine indications were normal at the time. Shortly thereafter, he observed noticeable variations in fuel flow accompanied by small variations in the right engine N1 (fan rotational speed) and N2 (turbine rotational speed). The captain reported that the right engine variations became significant and resulted in “yaw issues”; according to the first officer, the right engine was “pulsing.” The flight crew informed air traffic control (ATC) that they wanted to return to the departure airport. During this time the right engine power decreased to idle. The captain stated that about this time the right engine fuel flow indicator indicated 0 lbs/hr, indicating the engine flamed out. They declared an emergency and informed ATC they were unable to maintain altitude and would have to descend. The controller gave them an immediate clearance to descend. The captain stated they did not try to restart the right engine at this time because their altitude was above the restart envelope. He stated that as they descended the variations in parameters for the left engine were increasing and, after descending through FL300, they unsuccessfully attempted to restart the right engine. The variations in the left engine parameters continued to increase along with a decay in the max N1 and the engine was unresponsive to thrust lever movements. The crew then informed ATC that they needed to land at the nearest airport. The flight crew completed a successful emergency landing to a nearby airport, which resulted in no damage to the airplane and no injuries to the crew. The investigation found that the refueler had erroneously deposited diesel exhaust fluid into the FSII tank of his fuel truck, which he subsequently used to refuel 5 airplanes, including the incident airplane. Crystalline deposits were discovered in the fuel tank. Postaccident examination of the airframe and engines did not reveal contamination of the airframe filter elements; however, crystalline deposits began to appear on the elements about 5 months later. The reason for the latency was not determined. The rest of the fuel systems exhibited various quantities of crystalline deposits, with extensive formation at the fuel nozzles of both engines. The contamination at the nozzles would have interfered with the spray pattern of the affected nozzles, inhibiting their ability to atomize the fuel and resulting in the loss of power to both engines.

According to Safety Alert for Operators No. 18015, published November 13, 2018, by the Federal Aviation Administration: “DEF forms crystalline deposits that are not soluble in fuel, so they cannot be removed by flushing the aircraft fuel systems with jet fuel. Although the deposits are soluble in water and other polar solvents, use of these chemicals may have adverse consequences on aircraft and engine fuel system materials. Operators should contact Original Equipment Manufacturers (OEM) to develop inspection techniques and maintenance actions appropriate for each specific aircraft model type and its level of exposure.” Fueler Investigation According to the company that fueled the airplane, the fueling truck was quarantined immediately after the company was notified of the emergency landing. An immediate inspection of the quality records and analysis of JET A samples revealed that the fuel from the truck’s tank was clean and met industry standards. A field test of the fluid within the truck’s FSII reservoir showed a 30% concentration of DEF within the sample. According to the company, a laboratory test of a sample taken from the nozzle of the FSII tank showed a nitrogen content that exceeded 1.0, which suggests the presence of DEF. The fueler reported that a line service technician informed them that he was trying to be productive during a busy day and decided to make sure his truck had DEF. He located a container and inadvertently poured about 1 gallon of DEF into the FSII reservoir, which contained 1 gallon of FSII already inside the reservoir. The fueler stated that he was unfamiliar with DEF servicing as he had never serviced a truck with DEF before. The company’s investigation also discovered that the fueler had not seen the company’s internal bulletin on DEF contamination prevention and that he did not notice the label that showed the contents of the FSII tank. The fueler also noted that the position of the location of the FSII and DEF tanks on this truck were in opposite positions on another truck. A total of five airplanes were refueled with FSII (PRIST) from the contaminated fuel truck; however, none of the other affected airplanes were inspected as the refueler did not disclose their contact information. The incident airplane was the only airplane that was supplied with the contaminated fuel that reported a loss of power. Three of the operators confirmed to the refueler that they drained their fuel tanks and engine filters to remove the fuel. One operator removed approximately 200 gallons of the contaminated fuel and discovered crystalline contaminates within the filter vessels. Fuel System and Component Examinations The airplane was equipped with two tip tanks (357 gallons total), two wing tanks (374 gallons total), and a 200-gallon fuselage tank. Fuel was driven to the engine fuel nozzles via a low-pressure airframe fuel pump that directed fuel through a fuel filter (the low-pressure filter), a high-pressure fuel pump, a fuel control unit, and then a flow divider. Fuel Filters, Fuel Control Units, and Flow Dividers The left and right airframe and engine fuel filter elements were void of any debris. The airframe and engine filters were subsequently shipped to a secure facility where they were stored for a period of about 5 months, during which time there was extensive formation of crystalline deposits on all of the filters. An examination of the left engine’s fuel control unit (FCU), the left-engine fuel pump, and right- and left-engine flow dividers was completed 10 months after the incident. The left engine’s FCU plate valve inlet screen associated with the main fuel flow metering valve was mostly obstructed. The inlet screen associated with the main fuel flow metering valve and the fuel flow divider screen exhibited trace amounts of a substance that was hard, brittle, and mixed with jet fuel, giving it a gelatinous appearance. The right engine’s fuel flow divider inlet screen was mostly obstructed by the same substance. A bench test of the right engine’s FCU and fuel pump assembly showed that it was able to produce a fuel flow from 135 pph to 1985 pph. According to the engine manufacturer, max cruise flight requires a fuel flow of 615 pph. Fuel Nozzles According to the engine manufacturer, within each fuel nozzle there are two separate paths of fuel flow. The secondary fuel flows through the center of the fuel nozzle body while the primary fuel flows through a concentric path surrounding the center of the secondary fuel flow path. Both fuel flow paths contain a “last chance screen” for fuel to pass through before being introduced into the combustion chamber. During engine operation the primary and secondary fuel flows are directed to the 12 fuel nozzles. When the engine is started, fuel is directed through the primary fuel path, after which the secondary flow path is energized for engine acceleration. The primary and secondary flow paths, together, are used during all other times of engine operation. Both the left- and right-engine fuel nozzle assemblies were flow tested under 100 psi with the primary and secondary flow paths tested separately. A flow test and inspection of the right engine fuel nozzle assembly revealed that, during the primary flow test, nozzles 1, 3, 4 and 12 did not exhibit spray from either of the nozzle heads. Nozzles 5 and 6 dripped when tested. The secondary flow test revealed that nozzles 1, 3, and 11 did not spray, nozzles 2 and 12 exhibited an intermittent spray, nozzle 9 dripped, and nozzle 10 displayed as a stream. Four of the fuel nozzles were chosen for disassembly and further examination. All four fuel nozzles showed varying degrees of crystalline contaminates. According to the engine manufacturer, “functional flow testing of the [right-engine] fuel manifolds showed limited to no flow in all the primary and secondary fuel nozzles. Functional flow testing of the fuel manifolds showed limited to no flow in all the primary and secondary fuel nozzles. The fuel flow blockages observed would have prevented normal engine operation. Disassembly of 4 of the 10 fuel nozzles displayed crystalline contaminates in the primary and secondary fuel circuits.” The primary flow test of the left engine fuel nozzles showed that nozzles 1, 2, 4, 5, 6, and 12 exhibited no spray. Nozzles 3 and 10 displayed a “fair” spray quality and nozzle 9 was “dripping.” The secondary flow test revealed a “fair” spray quality from nozzles 2, 3, 4, 5, 9. Nozzles 1, 10, 11, and 12 exhibited “poor” spray quality. Only one of the 12 fuel nozzles met the specification requirements during testing. Four of the fuel nozzles were chosen for disassembly and further examination. All four fuel nozzles displayed crystalline contaminants in the primary and secondary fuel circuits. In their evaluation of the left engine’s fuel nozzles, the engine manufacturer noted, “Functional flow testing of the fuel manifolds from the left engine showed limited to no flow in all the primary and secondary fuel nozzles. The measured fuel flow and spray patterns observed would have prevented normal engine operation. Disassembly of 4 of the 10 fuel nozzles displayed crystalline contaminates in the primary and secondary fuel circuits.” On April 23, 2023, about 1729 Pacific daylight time, a Learjet 35A, N135SH, sustained an uncommanded decrease in power on both engines near Page, Arizona. The captain, first officer, and two medical crewmembers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight. According to the captain, the flight was a non-patient MEDEVAC flight destined for Chicago, Illinois. The captain placed a fuel order before the flight with Signature Aviation at Harry Reid International Airport (LAS), Las Vegas, Nevada, that included PRIST, a FSII; he observed the attendant write “T/O +” on the paperwork that pertained