What indicates a possible windshear condition during landing?

A difference between actual and reference ground speeds is indicative of a possible windshear condition during landing because windshear involves sudden changes in wind speed or direction. This can significantly affect the aircraft's ground speed during approach and landing phases.

When an aircraft experiences windshear, it may encounter increased headwinds or tailwinds unexpectedly. This leads to discrepancies between what the pilots expect (the reference ground speed) and what the instruments are showing (actual ground speed). For example, if there is a strong headwind that suddenly shifts or diminishes, the aircraft may experience an increased ground speed, while conversely, a sudden tailwind can lead to a reduced ground speed.

This phenomenon is crucial for pilots to recognize, as it can affect the aircraft's performance and stability during the critical landing phase, potentially leading to dangerous situations if not managed promptly. Understanding and identifying changes in ground speed relative to expectations can help aircrew prepare for and respond to these challenging atmospheric conditions.