Which instrument is NOT required for VFR day flight?

For VFR (Visual Flight Rules) day flight, certain instruments are required for safe operation, while others are not mandated by regulations. The correct answer highlights an instrument that is not a requirement for VFR operations during the daytime.

Landing lights are not a legal requirement for VFR flight in day conditions. While they can enhance safety and visibility, particularly for operations such as flying in proximity to other aircraft or during takeoff and landing, they are not listed among the essential equipment a pilot must have for VFR day flight under the regulations.

In contrast, an altimeter, oil pressure gauge, and airspeed indicator are essential instruments for any aircraft, regardless of the flight rules being followed. The altimeter is critical for maintaining proper altitude and awareness of air pressure changes. The oil pressure gauge is vital for monitoring engine health and ensuring proper lubrication—important for engine performance and safety. The airspeed indicator is crucial for understanding the aircraft's speed, which is fundamental for flight safety and performance management. Thus, these instruments are integral to a VFR day's flying requirements, whereas the landing lights serve a supplementary role.