Pilot, safety expert, consultant, and aviation journalist Stuart “Kipp” Lau writes about flight safety and airmanship for AIN.

Contributor - Safety

Stuart “Kipp” Lau

Fueling aircraft with the wrong type of fuel can lead to a complete loss of engine power causing serious injury or death. This is most critical when an aircraft powered by a reciprocating engine is fueled with kerosene-based jet-A fuel rather than aviation gasoline (avgas). According to the FAA, a reciprocating engine burning jet-A fuel at high power settings suffers detonations, rapid loss of power, and high cylinder head temperatures, quickly followed by a complete engine failure.
For a variety of reasons, according to investigators, reciprocating engine-powered aircraft continue to crash with the wrong type of fuel in their tanks. These crashes are often deadly since there is just enough avgas in the aircraft’s fuel system to take off and begin its initial climb. At a low altitude, the mixture of jet-A (versus avgas) can become great enough to cause an engine failure (or in the case of a multi-engine airplane, engine failures).
On Oct. 5, 2019, a Piper Aerostar 602P crashed less than four miles south of the Kokomo Municipal Airport (KOKK) in Kokomo, Indiana. The sole ATP-rated pilot was fatally injured in the crash. The National Transportation Safety Board (NTSB) reported the probable cause of the accident as “the pilot’s exceedance of the airplane’s critical angle of attack following a dual engine power loss caused by the line service technician fueling the airplane with the wrong fuel, which resulted in an aerodynamic stall and subsequent loss of control.” The report continued, saying, “Contributing (to the accident) was the pilot’s inadequate supervision of the fuel servicing.”
The line technician told investigators that when the aircraft arrived on the ramp in Kokomo, he parked the jet fuel truck in front of the Aerostar while the pilot was still inside the cockpit. The truck was marked with “JET-A” on both sides and on the rear of the vehicle.
New to the job and aviation, the line technician said, “The Aerostar looked like a jet airplane.” According to the line tech, the pilot was asked twice if he wanted jet fuel. The pilot responded “yes” and later ordered 163 gallons of fuel, according to the NTSB report. &nbsp;
Later that day, the accident pilot returned and prepped the aircraft for departure, started the engines, and began to taxi out to the runway for takeoff. Two witnesses said they heard the engines start up and they sounded “normal or typical.” Neither witness recalled seeing the aircraft takeoff.
Later, another witness told investigators she saw the Aerostar flying low and in a sharp turn to the left. At that point, both engines had failed, and the pilot faced a serious midair crisis. To land the aircraft, the pilot began to maneuver the aircraft, increased the bank angle, entered an accelerated stall, lost control, and crashed into a bean field. The aircraft was destroyed, and the pilot was killed.
Flared Peg, Round Hole
Beginning in the 1980s, industry began to develop and implement physical defenses (through service bulletins) to prevent “misfueling” events. Physical defenses included smaller fuel filler openings for aircraft requiring avgas and larger “flared” spouts on fueling equipment that dispenses jet-A fuel. The theory was these large fuel spouts could only fit in larger fuel filler openings on turbine-powered airplanes—those that required jet-A.
In the 1990s, size standards for fuel filler openings were incorporated into FAA Part 23 airworthiness standards. Airplanes with engines that require avgas must have openings no larger than 2.36 inches. Turbine-powered airplanes (not aircraft) could have an opening no smaller than 2.95 inches. At this time, the regulations also stated that each fuel filler opening must be placarded with the fuel type and minimum grade.
Again, this theory was sound; a big, flared jet-A fuel spout could not physically fit into the small fuel filler opening of an airplane requiring avgas.
However, these requirements did not apply to certain airplanes and rotorcraft powered by turbine engines that could not be fueled with the flared jet-A spout. This included aircraft manufactured before the new certification requirements or aircraft modified by replacing the reciprocating engine with a turbine engine (often retaining the smaller original fuel filler openings).
As a “workaround,” many jet-A fuel trucks and fixed fueling cabinets are equipped with a reduced-diameter spout that is intended to be used temporarily when the larger flared jet-A spout is impractical or unusable.
In the case of the inexperienced and unsupervised line technician in Kokomo, the jet-A truck had the appropriate flared nozzle and the aircraft had a smaller diameter filler opening. To “get the job” done, the line tech created his own workaround by positioning the “different shaped” spout at an angle over the wing fuel tank filler openings. According to the accident report, the line technician said he “initially spilled about one gallon of fuel during refueling and adjusted his technique so subsequent fuel spillage was minimal.”
Another problem, one that faced the line technician in Kokomo, is that many aircraft “look like a jet” with pointy noses and sleek lines. Adding to the confusion, many aircraft share the same or similar-looking fuselage but are powered by different engines—either reciprocating or turbine.
Examples include the single-engine Piper M-series and larger older twin Cessna and Piper aircraft. For the untrained eye, a piston-powered Piper M350 closely resembles a turbine-powered M500, a Cessna 421C Golden Eagle looks a lot like a Cessna 425 Conquest, and a Piper Navajo looks like a Cheyenne. In the same vein, a piston-powered Robinson R44 helicopter looks a lot like a turbine-powered R66.&nbsp;
For this reason, the FAA and some manufacturers encouraged operators to remove the words “turbo” or “turbo-charged” from the cowlings of turbocharged aircraft.
Inattention Blindness and Pilot Responsibilities
Pilots and fuel vendors have a shared responsibility to ensure that an aircraft is properly fueled. While the NTSB report on the Aerostar accident in Kokomo did not address the human factors issues that may have affected the pilot and influenced the accident, many of the “Dirty Dozen” human factors may be applicable.
The Dirty Dozen refers to the twelve most common human error preconditions (conditions that can act as precursors to accidents and incidents). From the NTSB report, several issues such as lack of communication, distraction, complacency, pressure, norms, and others may have been identified as precursors to this accident. It is difficult to determine since the pilot did not survive the accident.
A similar fueling accident occurred in 2015 near Thompson, Manitoba. This accident involved a scheduled flight in a Piper PA 31-350 Navajo that crashed shortly after takeoff. All eight occupants, including the pilots, survived with various serious injuries.
In this case, a new line technician fueled the aircraft with jet-A. The fueler had initially attempted to fuel the aircraft using the flared spout and switched to a smaller diameter spout to fit into the fuel filler opening. This defeated the defense to prevent jet-A from being used in a piston-powered aircraft.
During the fueling operation, both the captain and first officer were engaged in other duties. At one point, the first officer noticed the line technician having difficulties with the fuel filler openings. Accordingly, the first officer then “assisted the technician and asked for the required quantity.”
In its analysis of the accident, the Canadian Transportation Safety Board identified several factors that allowed a fueling error to go undetected. The report stated, “They included time pressure, the flight crew’s trust in the fuel dealer that was based on prior experience, and the direction of their attention to other work-related tasks at the time of fueling. These factors likely resulted in the inattention blindness that the crew members experienced toward the fuel truck signage that might have alerted them to the error of the fuel type.”
The FAA Airplane Flying Handbook (FAA-H-8083-38) recommends, “During refueling operations, it is advisable that the pilot remove all passengers from the aircraft during fueling operations and witness the refueling to ensure that the correct fuel and quantity is dispensed into the airplane and that any caps and cowls are properly secured after fueling.”
As a best practice, most large FBOs and fuel vendors incorporate several administrative defenses into fueling procedures to include, at a minimum, the following:
<ol>
<li>All orders shall include grade, volume and distribution, and aircraft registration.</li>
<li>The order shall be repeated back to the customer and recorded on the fuel order form.</li>
<li>All over-wing fueling requires a customer signature prior to fueling.</li>
<li>A requirement to log any removal and replacement of the flared jet-A spout with the smaller diameter spout.</li>
</ol>
According to the NTSB safety alert “Pilot: Fueling Mistakes,” a challenge for pilots is that it is difficult to identify that the wrong fuel has been pumped into an aircraft. Thus, it is important for pilots and line personnel to follow established best practices and maintain vigilance during fueling activities.
The NTSB alert also states, “Although jet-A fuel and avgas have distinct odors, colors, and evaporation properties, remember a visual check alone may not detect that jet-A and avgas have been mixed. The mixture can appear to be just avgas.”
Pilots should use caution and be alert to the fact that line technicians may not be aware of the fueling requirements of their specific aircraft. A line technician may be freshly trained. Often, this training can be completed in a week or two and consists of a series of videos, quizzes, and on-the-job training.
Fuel trucks should be clearly marked with the grade of fuel (jet-A or avgas) in their tank. Use caution if the truck is used to fuel smaller turbine-powered helicopters: it may have a smaller diameter spout installed rather than the larger flanged spout.
Pilots can use the fuel receipt as a final safety check to ensure that the aircraft was fueled properly. There have been several occasions where the accident pilot has signed a fuel receipt that clearly showed the wrong fuel was dispensed into the aircraft’s fuel tanks.
Finally, words matter. Pilots should listen up. If a line technician asks, “Do you want Prist with your jet,” this should be a red flag, and the pilot should request clarification. This was the case when an Alaska Division of Forestry Aero Commander 500S was fueled with jet-A. That aircraft crashed and seriously injured the pilot and three firefighters. &nbsp;
The opinions expressed in this column are those of the author and are not necessarily endorsed by AIN Media Group.

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