Abstract: Disclosed is a method of and apparatus for generating a signal representative of aircraft gear altitude after the flare maneuver is initiated in an automatic landing procedure. In accordance with the invention, the gear altitude signal is produced by complementary filtering of the aircraft gear altitude signal and the aircraft inertial vertical acceleration signal, with the complementary filter frequency being varied so that the aircraft filtered gear altitude signal primarily is produced on the basis of the vertical inertial acceleration signals prior to the time at which the aircraft reaches the runway threshold and is primarily produced on the basis of the aircraft gear altitude signal after the aircraft crosses runway threshold. The result is the reduction of the filtered gear altitude signal variation that can be caused by irregular terrain along the landing approach path while maintaining signal sensitivity to runway slope and runway slope variation.

Abstract: Disclosed is a method of and apparatus for determining the flare height at which the flare maneuver of an automatic landing procedure is initiated. The method includes the step of generating an adjusted approach sink rate signal, which depends on the ground speed of the aircraft during a landing approach and is compensated for short term deviations from the glideslope angle.