What is mast bumping?

Mast bumping refers specifically to a situation where the main rotor hub of a helicopter comes into contact with the mast, particularly during low-G flight conditions. This occurrence is a result of a sudden change in loading conditions on the rotor system, often experienced during abrupt maneuvers or turbulence when the helicopter experiences reduced rotor loading and weight on the rotor blades.

In low-G situations, the rotor blades can rise excessively, causing the rotor system to alter its alignment relative to the mast. If this misalignment becomes severe, it can lead to the rotor hub contacting the mast. This is a critical consideration for pilots, as mast bumping can lead to catastrophic rotor system failure and loss of control of the helicopter. Understanding this phenomenon is vital for ensuring safe flight operations, as it emphasizes the importance of managing G-load and maintaining proper flight attitudes.

The other choices describe different situations that do not accurately define mast bumping. They range from general flight instability to oscillations caused by turbulence, none of which captures the specific dynamics and risks associated with the rotor hub coming into contact with the mast during low-G conditions.