The frequency of aircraft accidents due to fuel mismanagement–which includes fuel starvation, fuel exhaustion, misfueling, or contamination–has declined substantially over the past eight years, according to the AOPA. While fuel mismanagement led to 101 accidents in 2011, there were just 29 in 2018, and fortunately, none of these were fatal.
Despite that positive news, challenges of misfueling continue to have an impact on the general aviation industry. Misfueling, or delivering the wrong type or grade of fuel to an aircraft, nearly always leads to a complete loss of engine power.
Which fuel is which?
It may be helpful to have a quick review of the types of aircraft fuels that can be mishandled to better understand the issue.
Avgas 100LL is a gas-based fuel most commonly used in piston engines within the general aviation community. It is dyed blue.
Jet fuel is a clear to straw-colored kerosene-based fuel and can be used in compression-ignition or turbine engines. It requires significantly higher temperatures than avgas to ignite.
While most commercial turbine engines can run on avgas within certain limitations, piston engines cannot run on jet fuel. With its extremely high flash point, jet fuel, in essence, creates a detonation that will cause a gas-based engine to misfire and eventually fail.
Unfortunately, even if misfueled, a piston engine will start and can operate correctly for a while, giving no warning that something might be amiss until it’s too late.
What are the causes of misfueling?
While there may be other, incidental origins of misfueling, some of most prominent reasons for misfueling include:
Miscommunication. Establishing a clear line of communication with FBO personnel is crucial to preventing misfueling situations. Be sure to communicate three key pieces of information: the fuel grade, the amount of fuel you need, and your aircraft’s tail number. Don’t become complacent and leave out information.
Modified fuel nozzles. The fuel nozzles for avgas and jet fuel are very different, and for good reason: to prevent mixing them up. Avgas nozzles are small and round to fit into the smaller filler ports of piston engine tanks. By contrast, jet fuel nozzles (often called J-Spout nozzles) are bigger and flattened, frequently compared to a duck’s bill. Thus, a jet fuel nozzle should never be able to fit in an avgas aircraft.
The problem here occurs when the standard J-Spout jet fuel nozzle is fitted with a round jet fuel nozzle, sometimes called a “rogue” nozzle. According to a NATA (National Air Transportation Association) safety briefing, one reason some line personnel might do this is because the J-Spout is not compatible with the ports of some helicopters. Instead of only using the rogue nozzle when needed, they leave it on. This practice is unsafe and increases the risk of misfueling accidents. Be sure the FBOs you choose are reputable and follow standard safety procedures.
Older or modified aircraft. While most of today’s aircraft have narrow, restricted filler port openings so the larger jet fuel nozzles cannot fit, some older aircraft may still have the larger openings. Likewise, when an aircraft engine is modified from a piston engine to a turbine one, some STCs do not require that the fuel filler port be changed to match the new type. Be aware if this is the case with your airplane and always give the line personnel clear instructions to avoid a misfueling situation.
What can pilots do to protect themselves?
One of the most basic safety measures is to be present every time your aircraft is fueled and follow these guidelines:
Fuel mismanagement may be rare these days, but we owe it to ourselves to remain vigilant every single time we fuel up to take to the skies.