Which instrument is NOT required for VFR OTT flight?

In VFR OTT (Visual Flight Rules Over The Top) flight, the objective is to operate visually while being above a layer of clouds or poor weather, which requires specific instruments for maintaining spatial orientation and control. The Attitude Indicator, Heading Indicator, and Turn Coordinator are essential for providing information about the aircraft's orientation and maneuvering, especially when visibility is limited.

The Attitude Indicator displays the aircraft's pitch and roll attitude, helping the pilot maintain the right orientation relative to the horizon. The Heading Indicator is crucial for navigation, displaying the aircraft's current heading. The Turn Coordinator assists in monitoring the rate of turn and helps maintain coordinated flight, which is vital in IFR conditions.

The Vertical Speed Indicator, while useful in general flight operations, isn't required for VFR OTT. This instrument indicates the rate of altitude change, which is less critical in maintaining visual flight rules and isolating flight from clouds or poor conditions. VFR OTT rules prioritize visual cues and basic aircraft control instruments that directly impact safety and navigation, and therefore, the Vertical Speed Indicator is not mandated for these operations.