Aviation Fuel Grades (AvGas & Jet-A)

Aviation fuels divide into two fundamentally different families, and the FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), Chapter 7, stresses that they are not interchangeable. Piston engines burn aviation gasoline, or AvGas, a high-octane, volatile gasoline. Turbine and turboprop engines, and aircraft diesels, burn a kerosene-based jet fuel. The two behave completely differently in an engine, and using the wrong one is a serious hazard.

AvGas is graded by its antidetonation performance, expressed as an octane or performance number, and each grade is dyed a distinctive color so it can be identified by sight. The historical grades are AvGas 80, dyed red; AvGas 100, dyed green; and AvGas 100LL, dyed blue. The letters LL stand for low lead. Today 100LL is by far the most widely available piston fuel and is the practical standard for the general-aviation training fleet, even though it still contains a small amount of tetraethyl lead, which higher-compression engines need to prevent detonation. The octane number matters because a fuel with too low a grade can allow detonation and destroy an engine, so an aircraft must be fueled with the minimum grade specified in its POH or a higher approved grade — never a lower one.

Jet fuel is a different product entirely. Jet-A, the standard grade in the United States, and Jet-A-1, common internationally with a lower freeze point, are kerosene-type fuels that are clear to straw or pale-yellow in color and are not dyed the way AvGas is. Jet-B is a wide-cut blend used in very cold climates. Jet fuel has a much higher flash point and lower volatility than AvGas and is meant for turbine combustion, not spark ignition. Because color alone can be ambiguous between straw-colored jet fuel and some contaminated or mixed products, airports use additional safeguards: fuel is labeled, and the industry uses differently sized and colored nozzles and placards, with AvGas dispensing equipment marked in one convention and jet fuel in another, to make cross-fueling physically and visually harder.

Lead in AvGas is being phased out, and several unleaded high-octane replacements have emerged to serve piston aircraft. Lower-octane unleaded grades such as UL91 and UL94 already serve many lower-compression engines, and higher-octane unleaded fuels intended as a full 100-octane, drop-in replacement for 100LL have been approved for fleetwide use through the supplemental type certificate process and industry initiatives, with the goal of an eventual transition away from leaded AvGas. Operators should confirm which fuels a given engine and airframe are approved to burn before adopting an alternative.

Misfueling — putting jet fuel into a piston aircraft, or the wrong grade of AvGas into any aircraft — is one of the more dangerous ground errors in aviation. A piston engine fed jet fuel may start and run briefly on residual AvGas, then lose power catastrophically after takeoff. This is why fuel type and grade are verified during preflight, why the fuel is sampled and checked for the correct color and for contamination, and why line-service procedures, placards, and nozzle standards all exist to prevent the wrong fuel reaching the wrong tank.

For a flight school or flying club, fuel is both a major recurring cost and a live safety issue, and both sides run through the operation daily. On the cost side, AvGas price movements feed straight into aircraft operating cost and rental rates, and a school that self-fuels or manages fuel accounts has to reconcile fuel purchased against fuel burned across the fleet. On the safety side, misfueling is a low-probability, high-consequence event that student pilots, renters, and line staff must be trained to guard against, especially at fields that dispense both AvGas and jet fuel or where self-service and full-service pumps sit side by side.

The leaded-to-unleaded transition adds a current, practical dimension. As unleaded grades become available, a school must know exactly which of its engines and airframes are approved for which fuel, keep those approvals on record, and brief instructors and renters accordingly, because putting an unapproved grade in an engine is the same category of error as any other misfueling. Clear per-aircraft fuel records and consistent preflight fuel checks are the defenses.

Aviatize's Digital Data & Records module keeps each airframe's approved fuel grades and any unleaded-fuel supplemental type certificates on file alongside the aircraft's other documents, so instructors, renters, and line staff can confirm the correct fuel for a specific tail number rather than relying on memory during a busy turnaround.

Aviatize's Billing & Payments and KPI Reporting & Dashboards modules tie fuel cost into aircraft operating cost and rental rates, so an operator can see fuel burn and cost per hour across the fleet, reconcile fuel accounts, and reflect fuel-price movements in pricing, while Training Management can carry fuel-verification and misfueling-awareness items in the syllabus.