What minimum required markings must be placed at or near each appropriate fuel filler cover for reciprocating engine-powered airplanes?

Reciprocating engine-powered airplanes specifically require markings that clearly indicate the type of fuel appropriate for that aircraft. The phrase "Avgas" is short for aviation gasoline, which is the correct designation for the fuel used in reciprocating engines. This is vital for safety, as using the wrong type of fuel could have catastrophic consequences.

Marking the fuel filler cover with "Avgas" along with the minimum fuel grade helps ensure that ground personnel and pilots can quickly and accurately identify the appropriate fuel. This is especially important in busy environments where multiple types of aircraft may be present, reducing the likelihood of fuel contamination or mis-fueling incidents.

The other terms associated with the other options do not apply to reciprocating engines; they refer to different types of fuels used in aviation and are therefore not relevant for these aircraft. The need for clear, specific identification of fuel types at filling points is paramount for the operational integrity and safety of the aircraft.