The Wrong Fuel — Misfueling and Fuel Contamination in General Aviation

PATTERN CARD. Piston aircraft engines detonate and quit on jet fuel, and the industry's physical guard — a fat "duck's bill" Jet A nozzle that cannot enter a small avgas filler port — keeps being defeated on the ramp: FBOs modify jet-fuel nozzles with smaller round spouts to service turbine helicopters, and turbine-conversion STCs leave avgas-sized filler ports on airplanes that now need Jet A (NTSB Safety Alert SA-050). In the anchor case, an air-ambulance Cessna 421C at Las Cruces was fueled with 20 gallons of Jet A per wing from a truck whose nozzle had been permanently modified to a round spout — past filler labels reading "AVGAS ONLY", with the pilot standing there helping replace the fuel caps. Both engines detonated and lost power on initial climb; the pilot, two medical crewmembers and one patient died. Water and sediment contamination belong to the same family: the wrong or dirty fluid delivered during servicing, invisible once the caps go back on.

The NTSB found the responsibility joint — the line technician who pumped it, the pilot who supervised it, and the FBO that modified the nozzle all contributed (NTSB CEN14FA462, probable cause). Misfueling is a servicing error that recurs often enough that the NTSB issued a standing Safety Alert with four investigations from 2009–2015 and traced its recommendations back to the 1980s (SA-050; recommendations A-82-140, A-82-141, A-86-135). A visual check of the tank may not catch it: a Jet A/avgas mixture can look like plain avgas (SA-050).

1. Confirm the aircraft registration, required fuel grade and which tanks to fill with the placards and the pilot before dispensing — never fuel from assumption or aircraft resemblance.
2. Match nozzle to port and respect the mismatch: a jet-fuel nozzle that slips into an avgas filler is the alarm itself. Never operate modified or reduced jet nozzles on avgas-capable ramps.
3. Know your STC traps: a converted airframe can look identical to its piston sibling — check the data plate and placards, not the silhouette.
4. Write the truth on the ticket and read it back: the fuel receipt names the fuel that actually went in, and pilots have signed receipts saying "Jet A" without noticing.
5. Treat post-fueling checks honestly — sump and smell, but remember a mixture can pass a visual check; the paperwork and the dispensing truck are the real trail.

Total frequency is not quantified in public sources — but the NTSB found the pattern recurrent enough for a standing Safety Alert citing four misfueling investigations between 2009 and 2015, two of them fatal, plus safety recommendations dating to the 1980s (NTSB Safety Alert SA-050, March 2016).

In the anchor case the misfueled Cessna 421C lost power in both engines on initial climb out of Las Cruces; it struck terrain upright and burned. All four aboard — pilot, two medical crewmembers, one patient — were killed. Investigators smelled jet fuel at the wreckage the next day, and post-accident engine examination showed internal damage and evidence of detonation (NTSB CEN14FA462).