Final answer:
Decreasing performance windshear is a weather phenomenon that can rapidly reduce aircraft lift during critical phases of flight. Pilots are alerted to its presence by auditory and visual annunciations in the cockpit, allowing them to take the necessary actions to maintain control and safety of the aircraft.
Step-by-step explanation:
Decreasing performance windshear is a dangerous weather phenomenon that pilots may encounter during takeoff or landing. It occurs when there is a sudden change in wind speed and/or direction that can lead to a rapid decrease in lift, making it difficult to control the airplane. The annunciations, or warnings, typically provided to the pilot in a modern aircraft when encountering this type of windshear include auditory alerts such as "Windshear, Windshear, Windshear," and visual alerts on the cockpit instruments. There may also be reactive guidance provided by the aircraft's flight systems to help the pilot navigate out of the windshear situation safely.
It is important for pilots to recognize these annunciations promptly and perform the appropriate windshear escape maneuver, which usually involves applying maximum thrust and pitching the aircraft to maintain or achieve a climb. The proper training for recognizing and responding to windshear is critical for flight safety.