What does the estimated ground speed refer to in a flight progress strip?

The estimated ground speed refers to the speed at which an aircraft is expected to travel over the ground, which is specifically indicated on a flight progress strip. This measurement is crucial for air traffic controllers as it helps them determine the aircraft's movement relative to the Earth’s surface, allowing for better scheduling and separation of flights. Ground speed can be affected by various factors, including wind conditions and the aircraft's performance characteristics, which is why it is important to monitor this figure closely.

The other options relate to different aspects of flight parameters. The projected altitude pertains to how high the aircraft is expected to fly, the time to cruise altitude focuses on climb times, and wind speed at cruising altitude deals with atmospheric conditions rather than the aircraft’s speed relative to the ground. Recognizing these distinctions is essential for understanding the operation and regulation of air traffic.