What are the lights perpendicular to the runway approach lights?

The correct answer identifies crossbar lights, which are specifically designed to assist pilots during the approach phase of landing. These lights typically provide additional visual guidance and help define the centerline of the runway, enhancing visibility as the aircraft descends.

Crossbar lights are strategically placed perpendicular to the runway approach lights, which aids pilots in aligning their approach properly while descending. Their positioning also helps to delineate the intended path of the aircraft, thereby contributing to greater safety during landings.

Other options do not fit this specific definition. For instance, beacon lights typically provide broader location illumination and may serve as warnings rather than directing approach paths. Approach lights extend in a line typically leading to the runway to assist with visual guidance for landing but are not perpendicular. Threshold lights are located at the beginning of the runway and indicate the runway’s usable length but do not serve the same function as crossbar lights in terms of alignment during the approach phase.