Final answer:
When a mechanic taxiing an aircraft sees a flashing red light from the control tower, they must clear the runway immediately as it's a signal for potential danger or to prevent interference with operational procedures.
Step-by-step explanation:
A mechanic taxiing an aircraft on a runway who receives a flashing red light from the control tower is being instructed to clear the runway immediately. This light signal is part of standardized airfield driving procedures and is critical for maintaining safety on runways and taxiways. The mechanic must promptly acknowledge the signal and vacate the runway to avoid potential collisions or disruptions to airport operations.