There are two air pressure ports, each on separate faces of the probe, which are piped to the instrument display. The differential pressure between the two ports yields lift reserve readouts. The LRI display consists of a single arc divided into three sectors. The Red sector of the arc indicates that the airplane is no longer generating sufficient lift to sustain level flight. At the top of the Red sector, just below where it meets the White sector, the airplane is sinking.
Sink is imperceptible.
Deeper into the Red sector the airplane approaches full stall. During takeoff when the LRI needle clears the Red sector and enters the White sector, the airplane has sufficient lift for takeoff. The White sector of the display is the slow speed region of the aircraft. It is the region just above zero lift reserve . During takeoff and climbout this sector of the display indicates Rotation Liftoff Maximum angle of climb During approach and descent, flying the airplane in the White sector of the gauge allows the aircraft to safely dissipate the kinetic energy of lift producing the slowest approach and shortest rollout.