Abstract: In an aircraft terrain warning system utilizing a radar altimeter wherein the rate of closure to the terrain is compared with the aircraft's altitude above the terrain to generate a warning signal when the closure rate is excessive for a particular altitude, the closure rate signal is limited and biased depending upon the aircraft's closure rate and configuration in order to significantly increase the time response of the system while at the same time reducing nuisance warnings. The amplitude limit on the closure rate signal, is varied, above a predefined altitude, as a function of the closure rate signal in oreder to provide increased warning times at greater closure rates. Circuitry, responsive to the aircraft's flap positions, is also provided to alter the characteristics of rate limiter so as to provide warning parameters that more accurately reflect operating conditions at lower aircraft speeds.

Abstract: In a terrain warning system wherein the rate of the aircraft's closure to the terrain is compared to the aircraft's altitude above the terrain in order to generate a warning signal for excessive closure rates, a circuit is provided to inhibit the warning signal when the aircraft begins to climb in response to the warning signal and to measure the altitude gained by the aircraft resulting in the reactivation of the warning signal if the aircraft has leveled off before gaining a predetermined amount of altitude. The circuit includes: a memory element to indicate that a warning signal has been generated; a circuit to generate a climb signal in response to a barometric rate of change signal indicating the aircraft is climbing; and an integrating circuit responsive to the barometric rate signal to determine the amount of altitude the aircraft has gained while climbing.