What minimum markings must be placed at or near fuel filler covers for reciprocating engine-powered airplanes?

The correct answer identifies the requirement to label fuel filler covers with the word 'Avgas' along with the minimum fuel grade. This is essential for safety and operational integrity in aviation.

Reciprocating engine-powered airplanes primarily use aviation gasoline (Avgas), and clear labeling is crucial to prevent the potential misuse of incorrect fuels. By indicating 'Avgas' and specifying the minimum fuel grade, the markings ensure that pilots and ground crew can quickly and accurately identify the appropriate fuel to use. This is vital since using a fuel with a lower grade than required could lead to engine performance issues, knock, or even engine failure.

Effective labeling at fuel filler covers helps to promote safe fueling practices and minimizes the risk of accidents arising from fuel misidentification. Such measures are part of broader efforts to maintain safety standards in aviation operations, thereby protecting both the airframe and the lives of those onboard.