According to aviation regulations, what marking is mandatory for oil tank fillers on turbine engines?

The marking "Oil" is mandated for oil tank fillers on turbine engines for several critical reasons related to safety and operational efficiency. This clear designation helps to prevent any potential mix-ups with fuel, which could lead to catastrophic consequences if the incorrect substance is added to the engine. Since turbine engines operate with oil separate from the fuel system, labeling the filler specifically as "Oil" ensures that personnel can quickly and accurately identify the correct fluid for maintenance and servicing.

Additionally, regulations require that any systems and components must be clearly labeled to enhance safety protocols, reduce the risk of human error during fueling or servicing procedures, and ensure compliance with industry standards. This dedicated labeling fosters a safer operating environment by reinforcing proper maintenance practices, thus promoting the longevity and reliability of the engine.

The other choices, while relevant to different contexts, do not specifically denote oil in the context of turbine engine maintenance and servicing, which emphasizes the necessity of accurate and clear labeling.