Runway centerline lights as seen from the flight deck begin to alternate white and red in the last what distance of runway?

Runway centerline lights serve as a critical visual aid for pilots during the landing phase, particularly when the visibility may be compromised. The specific function of alternating white and red lights is to signal that the aircraft is approaching the runway's end and to warn pilots of the remaining distance available for landing.

In this case, the correct answer indicates that the alternating pattern of white and red lights begins to appear at a distance of 3,000 feet remaining on the runway. This criterion is established to provide ample time for pilots to execute go-around procedures if necessary, or to adjust their approach if they find themselves too close to the runway threshold.

The choice of 3,000 feet is integral to runway operations because it aligns with safe landing practices, ensuring pilots have adequate visual cues to assess their approach. Thus, the specific threshold of distance remaining is not arbitrary but is based on standardized operational protocols designed for safety in aviation.