Avgas is gasoline fuel for reciprocating piston engine aircraft and is not to be confused with jet fuel. As with all gasoline’s, avgas is very volatile and is extremely flammable at normal operating temperatures. Procedures and equipment for safe handling of this product must therefore be of the highest order.
Avgas grades are defined primarily by their octane rating. Two ratings are applied to aviation gasolines (the lean mixture rating and the rich mixture rating) which results in a multiple numbering system e.g. Avgas 100/130 (in this case the lean mixture performance rating is 100 and the rich mixture rating is 130).
In the past, there were many different grades of aviation gasoline in general use e.g. 80/87, 91/96, 100/130,108/135 and 115/145. However, with decreasing demand these have been rationalized down to one principle grade, Avgas 100/130. (To avoid confusion and to attempt to eliminate errors in handling aviation gasoline, it is common practice to designate the grade by just the lean mixture performance, i.e. Avgas 100/130 becomes Avgas 100). More recently, an additional grade was introduced to allow one fuel to be used in engines originally designed for grades with lower lead contents: this grade is called Avgas 100LL, the LL standing for ´low lead´.
All equipment and facilities handling avgas are color coded and display prominently the API markings denoting the actual grade carried. Currently the two major grades in use internationally are Avgas 100LL and Avgas 100. To ease identification the fuels are dyed; for example Avgas 100LL is colored blue, while Avgas 100 is colored green.
Avgas fuelling nozzles for over wing dispensing are painted red. To help prevent the possibility of jet fuel being supplied to a piston engine aircraft, the nozzle of an Avgas fuller is limited to a maximum diameter of (internationally) 40 mm (49 mm in U.S.A) and the aperture on an aircraft Avgas tank to a maximum of 60 mm diameter. Nozzles for Jet A-1 are larger than 60 mm and thus cannot be placed into an aircraft´s Avgas tank.