Definition
A cockpit warning system that monitors the aircraft's height above terrain using a radio altimeter and aircraft configuration data, and issues aural and visual alerts when it detects an unsafe relationship between the aircraft and the ground — such as excessive descent rate, excessive terrain closure rate, descent after takeoff, unsafe terrain clearance while not in landing configuration, or excessive deviation below the glideslope.
Plain English
A system that watches how close the aircraft is to the ground and shouts a warning if it looks like the aircraft is about to hit terrain.
Context Anchor
Seen in instrument flying, approach, and aircraft systems discussions, especially when learning about cockpit warning systems that protect against controlled flight into terrain.
Derivation
“Ground” means the earth’s surface, “proximity” means nearness, and “warning system” means equipment that alerts the crew. “Proximity” comes from a Latin word meaning “nearest,” which helps anchor the idea: GPWS is about unsafe nearness to the ground.
Why Pilots Care
Provides the last line of defense against controlled flight into terrain accidents, especially at night or in poor visibility.
Grounding Statement
GPWS is a last-chance cockpit warning that tells the crew, in effect, “You are too close to the ground for what the airplane is doing right now.”
Intuition Check
Do not think of GPWS as a system used only during landing. It can warn during other phases of flight whenever the aircraft’s path or height makes ground contact a danger.
Example Sentence 1
On final approach the GPWS called 'SINK RATE', and the pilot reduced the descent rate before continuing.
Example Sentence 2
During the non-precision approach, the crew relied on the GPWS to confirm safe terrain clearance.