Zero lift reserve occurs when either airspeed is so low or angle of attack so high that if airspeed is reduced or angle of attack increased the aircraft ceases to generate sufficient lift to sustain level flight. The aircraft begins to sink entering the region of full stall. Zero Lift Reserve is equal to one G.
The LRI is reliable under all conditions of weight, center of gravity, flap position, air density, turbulence and angle of bank. In windshear conditions the LRI immediately informs a pilot of loss of lift and possible impending stall. As angle of attack is reduced to compensate for sudden loss of aircraft performance, the LRI confirms recovery.