Which of the following is NOT a visual reference required for descent below MDA?

The correct answer is grounded in an understanding of the visual references that are essential for safely descending below the Minimum Descent Altitude (MDA) during an instrument approach. When flying under IFR and prepared to make a landing, pilots must confirm specific visual cues to ensure they are able to safely continue the approach and make a landing.

Runway end identification lights, PAPI (Precision Approach Path Indicator) or VASI (Visual Approach Slope Indicator) lights, and threshold markings all provide critical visual indications of lateral and vertical alignment with the runway. These references help pilots assess their position relative to the runway environment and confirm that it is safe to land.

In contrast, ground speed indication lights do not serve as a visual reference for descending below MDA. These indicators relate to the aircraft's speed over the ground, which, while important for overall operation and performance, does not provide direct information on the runway’s position or configuration. Ground speed is primarily a tool for managing approach and landing performance but does not fulfill the visual reference criteria necessary for descending safely below MDA. Thus, recognizing that ground speed indication lights are not a required visual reference is key to understanding the parameters set for a safe approach and landing.