Aircraft Systems

Fuel Strainers, Sumps, and Drains performs the same as grade 100, the “LL” indicates it has After leaving the fuel tank and before it enters the carburetor, a low lead content. Fuel for aircraft with turbine engines is the fuel passes through a strainer that removes any moisture classified as JET A, JET A-1, and JET B. Jet fuel is basically and other sediments in the system. Since these contaminants kerosene and has a distinctive kerosene smell. Since use of are heavier than aviation fuel, they settle in a sump at the the correct fuel is critical, dyes are added to help identify the bottom of the strainer assembly. A sump is a low point in a fuel type and grade of fuel. [Figure 7-32] system and/or fuel tank. The fuel system may contain a sump, a fuel strainer, and fuel tank drains, which may be collocated. In addition to the color of the fuel itself, the color-coding system extends to decals and various airport fuel handling The fuel strainer should be drained before each flight. Fuel equipment. For example, all AVGAS is identified by name, samples should be drained and checked visually for water using white letters on a red background. In contrast, turbine and contaminants. fuels are identified by white letters on a black background. Water in the sump is hazardous because in cold weather the Special Airworthiness Information Bulleting (SAIB) water can freeze and block fuel lines. In warm weather, it NE-11-15 advises that grade 100VLL AVGAS is acceptable can flow into the carburetor and stop the engine. If water is for use on aircraft and engines. 100VLL meets all present in the sump, more water in the fuel tanks is probable, performance requirements of grades 80, 91, 100, and 100LL; and they should be drained until there is no evidence of water. meets the approved operating limitations for aircraft and Never take off until all water and contaminants have been engines certificated to operate with these other grades of removed from the engine fuel system. AVGAS; and is basically identical to 100LL AVGAS. The lead content of 100VLL is reduced by about 19 percent. Because of the variation in fuel systems, become thoroughly 100VLL is blue like 100LL and virtually indistinguishable. familiar with the systems that apply to the aircraft being flown. Consult the AFM/POH for specific operating procedures. Fuel Contamination Accidents attributed to powerplant failure from fuel Fuel Grades contamination have often been traced to: Aviation gasoline (AVGAS) is identified by an octane or • Inadequate preflight inspection by the pilot performance number (grade), which designates the antiknock • Servicing aircraft with improperly filtered fuel from value or knock resistance of the fuel mixture in the engine small tanks or drums cylinder. The higher the grade of gasoline, the more pressure the fuel can withstand without detonating. Lower grades of • Storing aircraft with partially filled fuel tanks fuel are used in lower-compression engines because these • Lack of proper maintenance fuels ignite at a lower temperature. Higher grades are used in higher-compression engines because they ignite at higher Fuel should be drained from the fuel strainer quick drain and temperatures, but not prematurely. If the proper grade of fuel from each fuel tank sump into a transparent container and is not available, use the next higher grade as a substitute. Never then checked for dirt and water. When the fuel strainer is use a grade lower than recommended. This can cause the being drained, water in the tank may not appear until all the cylinder head temperature and engine oil temperature to exceed fuel has been drained from the lines leading to the tank. This their normal operating ranges, which may result in detonation. indicates that water remains in the tank and is not forcing the fuel out of the fuel lines leading to the fuel strainer. Therefore, Several grades of AVGAS are available. Care must be drain enough fuel from the fuel strainer to be certain that exercised to ensure that the correct aviation grade is being fuel is being drained from the tank. The amount depends on used for the specific type of engine. The proper fuel grade is stated in the AFM/POH, on placards in the flight deck, and next to the filler caps. Automobile gas should NEVER be used in aircraft engines unless the aircraft has been modified 80 100 100LL JET AVGAS AVGAS AVGAS A with a Supplemental Type Certificate (STC) issued by the Federal Aviation Administration (FAA). COLORLESS RED GREEN BLUE OR STRAW The current method identifies AVGAS for aircraft with AVGAS AVGAS AVGAS reciprocating engines by the octane and performance number, JET A 80 100 100LL along with the abbreviation AVGAS. These aircraft use AVGAS 80, 100, and 100LL. Although AVGAS 100LL Figure 7-32. Aviation fuel color-coding system. 7-27