Abstract: In an excessive descent-rate warning systems particularly useful for helicopters, a descent-rate signal is produced corresponding to the rate of change of altitude, and is used for producing a warning signal whenever the descent-rate exceeds the maximum one for the respective altitude according to a predetermined relationship which relationship includes an offset value defining the maximum descent rate at "0" altitude. An increase in the forward-speed of the aircraft is used to reduce the offset in the above predetermined relationship, and thereby to decrease the maximum descent rate at "0" altitude producing the warning signal. A described system may be operated according to a "Take-Off Mode" effective upon take-off to cause a warning signal to be produced upon any descent of the aircraft until it reaches a preselected altitude, at which time the system is automatically actuated to operate according to the above-described Flight Mode.