Every aviation fuel grade has a specific color, a specific octane or energy rating, and a specific set of engines it is designed to serve. These are not arbitrary marketing choices — they are a carefully engineered system of safeguards that begins at the refinery and ends at the fuel nozzle in your hand. For an Aviation Maintenance Technician (AMT) working on airframe fuel systems, understanding fuel grades and color-coding is a fundamental safety responsibility. A misfueling event — putting the wrong fuel in an aircraft — can cause detonation, engine failure, or a catastrophic in-flight emergency. Recognizing the correct fuel by its appearance, smell, and labeling is one of the most practical tools a technician, line worker, or pilot can use.
This article covers the grades of aviation gasoline (avgas) and aviation turbine fuel (jet fuel) used in civil aviation, how each is identified, what the color-coding standards mean, and why every person who touches an aircraft fuel system must know these facts cold.
Aviation Gasoline (Avgas) Grades and Colors
Avgas is designed for reciprocating (piston) aircraft engines. Its most critical specification is its antiknock rating, expressed as an octane or performance number, because piston engines are susceptible to detonation — uncontrolled combustion that can destroy pistons and cylinders in seconds. The higher the rating, the more resistant the fuel is to detonation under high compression and high manifold pressure.
Historically, several avgas grades existed (80, 100, 100LL, 115, and others), but the modern fleet has largely consolidated around two grades that remain in widespread use:
- Avgas 100LL (Low Lead) — Blue: This is by far the most common avgas in use today. The designation "100" refers to its lean-mixture octane rating of 100, and "LL" stands for low lead — it contains a reduced concentration of tetraethyllead (TEL) compared to the older Grade 100. Its standardized color is blue. Because it is so prevalent, student pilots and technicians sometimes assume all avgas is blue, which is a dangerous misconception.
- Avgas 100 (High Lead) — Green: The older Grade 100 avgas, sometimes still encountered, shares the same 100-octane lean rating as 100LL but contains a higher TEL concentration. Its standardized color is green. Many older high-performance radial and large reciprocating engines were certified for this grade, though its use has declined significantly.
- Avgas 80 — Red: Grade 80 is a lower-octane fuel with a lean-mixture rating of 80 and a rich-mixture rating of 87 (written as 80/87). It was designed for lower-compression reciprocating engines. Its standardized color is red. Grade 80 has become very rare in the United States, but technicians may still encounter it in legacy documentation and must know it is red and must never be placed in an engine certified for 100 or 100LL.
A critical rule: never use a lower-grade avgas in an engine certified for a higher grade. Using 80-octane fuel in a high-compression engine requiring 100LL invites immediate detonation. The reverse — using 100LL in an engine certified for 80 — is permissible in many cases per the aircraft's approved fuel list, but always verify the aircraft's Type Certificate Data Sheet (TCDS) and the engine manufacturer's approved fuel list before substituting grades.
Color is the first line of defense, but it is not infallible — fuel can be contaminated or mislabeled. Always verify fuel grade through labeling on sumped samples, fuel trucks, and bulk storage containers. The color of a properly drawn fuel sample in a clear sump cup should match the expected grade color when viewed in daylight.
Jet Fuel Grades and Colors
Aviation turbine fuel (jet fuel) is used in turbine-powered aircraft — jets, turboprops, and turbine helicopters. Turbine fuels are kerosene-based or kerosene/naphtha blends. They do not have an octane rating; instead, their specifications center on energy content, freeze point, flash point, viscosity, and thermal stability. The grades most relevant to civil aviation in the United States are:
- Jet-A — Colorless to straw/pale yellow: This is the standard turbine fuel used throughout the United States and most of the world. It is a kerosene-type fuel with a freeze point of -40°C or colder. Under most lighting conditions Jet-A appears clear to very light straw or pale yellow in a sump cup. It has no dye added in its base specification, so its nearly clear appearance is itself an identifier.
- Jet-A1 — Colorless to straw/pale yellow: Jet-A1 is the international standard turbine fuel, required outside the United States on most international routes. Its freeze point specification is colder (-47°C) than Jet-A, making it better suited for high-altitude, long-duration polar routes. In appearance, Jet-A1 is essentially identical to Jet-A — both are clear to pale straw — which means the labels on fuel trucks and storage tanks are critical for distinguishing them.
- Jet-B — Colorless to straw/pale yellow: Jet-B is a wide-cut turbine fuel (a blend of naphtha and kerosene) with a lower freeze point and higher volatility than Jet-A. It is primarily used in very cold climates (notably parts of Canada and Alaska) where Jet-A's cold-flow properties are insufficient. Its appearance is similar to Jet-A but its volatility makes it more hazardous to handle. Jet-B is rarely encountered in the contiguous United States.
Unlike avgas, most jet fuels rely on labeling and nozzle design rather than color coding to prevent misfueling. The fuel industry uses large-diameter (greater than 2.85 inches) nozzles for jet fuel and smaller nozzles for avgas, providing a physical interlock — a Jet-A nozzle will not fit into a typical avgas filler neck. However, this system is not foolproof, and a technician must always confirm fuel type through markings on the fuel truck, the storage tank placard, and the aircraft's approved fuel list.
Why Color-Coding Matters: Misfueling Prevention
Misfueling is one of aviation's most preventable — and most deadly — mistakes. Putting jet fuel into a piston aircraft is particularly dangerous: jet fuel (kerosene) has a much higher flash point and far lower volatility and antiknock quality than avgas, so a spark-ignition reciprocating engine fueled with jet fuel will struggle to vaporize and ignite the mixture properly and is highly prone to detonation and pre-ignition, typically resulting in rough running, loss of power, or engine failure shortly after or during takeoff. The reverse scenario — avgas loaded into a turbine engine — is actually the more commonly documented misfueling accident, since turbine engines will often start and run on avgas long enough for takeoff before the tetraethyllead fouls hot-section components and causes an in-flight failure, making it especially insidious. The color-coding system for avgas and the physical nozzle-sizing system for turbine fuels exist precisely to create multiple independent barriers against misfueling. As an AMT, part of your responsibility during a fuel system inspection or servicing operation is to:
- Confirm the fuel grade listed on the aircraft's TCDS and the approved airplane flight manual (AFM).
- Visually inspect the color of a sumped fuel sample and compare it against the expected color for the approved grade.
- Verify fuel truck and storage tank markings match the required fuel type before any fueling begins.
- Check that fuel caps are properly secured and fuel vent lines are unobstructed after servicing.
Key Numbers and Rules
- Avgas 100LL — Blue — lean octane 100, most common avgas worldwide.
- Avgas 100 (High Lead) — Green — lean octane 100, higher TEL content, declining in use.
- Avgas 80 (80/87) — Red — lean octane 80, low-compression engines, very rare today.
- Jet-A — clear to pale straw, freeze point -40°C, U.S. standard turbine fuel.
- Jet-A1 — clear to pale straw, freeze point -47°C, international standard.
- Jet-B — clear to pale straw, wide-cut, used in extreme cold climates.
- Avgas nozzle diameter is smaller than jet fuel nozzle diameter — a physical misfueling barrier.
- Always cross-reference the aircraft TCDS for the approved fuel grade before servicing.
- Never use a lower avgas grade than approved; confirm any upward substitution with the engine manufacturer and TCDS.
Common Test Traps
- Confusing 100 and 100LL colors: Both grades are rated at 100 octane (lean mixture), but 100LL is blue and Grade 100 is green. The LL designation means low lead, not a different octane. This distinction is a frequent test question.
- Assuming all jet fuel is color-coded: Unlike avgas, jet fuels are not distinctively dyed by grade. Jet-A, Jet-A1, and Jet-B all appear clear to pale straw. Identification depends on labels, not color alone.
- Mixing up Grade 80's color: Grade 80 is red — not to be confused with the red used on fire extinguishers or warning labels. Students sometimes guess orange or pink. It is definitively red.
- Believing nozzle sizing alone prevents misfueling: Physical nozzle interlock reduces but does not eliminate misfueling risk. Human error, non-standard equipment, and improper procedures can still result in the wrong fuel being loaded. Always verify labels and fuel sample color.
- Using a lower-grade avgas in a high-compression engine: Technicians sometimes assume any avgas will work in any piston engine. Using 80/87 in an engine requiring 100LL can cause immediate detonation and engine failure. Always consult the TCDS and AFM.