GPWS

Ground proximity warning system (GPWS) is a system designed in 1967 by Don Bateman Chief Engineer, Flight Safety Avionics, Honeywell to alert pilots if their aircraft is in immediate danger of flying into the ground. Another common name for such a system is ground-collision warning system (GCWS). The system monitors an aircraft's height above ground as determined by a radar altimeter. A computer then keeps track of these readings, calculates trends, and will warn the captain with visual and audio messages if the aircraft is in certain defined flying configurations ("modes").The modes are:Excessive descent rate ("PULL UP" "SINKRATE")Excessive terrain closure rate ("TERRAIN" "PULL UP")Altitude loss after take off ("DON'T SINK")Unsafe terrain clearance ("TOO LOW - TERRAIN" "TOO LOW - GEAR" "TOO LOW - FLAPS")Excessive deviation below glideslope ("GLIDESLOPE")Bank angle protection ("BANK ANGLE")Windshear protection ("WINDSHEAR")
See more at Wikipedia.org...

Ground Proximity Warning System