What consequence can result from experiencing windshear during flight?

Experiencing windshear during flight can lead to a sudden loss of airspeed and altitude due to the rapid changes in wind direction and speed that characterize this phenomenon. Windshear often occurs during takeoff or landing phases when an aircraft is operating at lower altitudes and speeds, making it particularly vulnerable. These abrupt changes can result in a dramatic increase in lift or a rapid loss of it, potentially causing the aircraft to stall or descend unexpectedly. Pilots must be vigilant and prepared for such conditions, as they can significantly affect the aircraft's performance and control.

The other options do not accurately reflect the effects of windshear. For example, a decrease in fuel efficiency might occur in various flight circumstances but is not a direct consequence of windshear. Similarly, an increase in engine performance or aircraft stability is not associated with windshear, as the issue is primarily related to fluctuating aerodynamic conditions rather than improved performance or stability. Therefore, the correct answer highlights the immediate and severe risks posed by windshear during flight operations.