Definition
Onboard avionics that monitor an aircraft's position and altitude relative to the ground and surrounding terrain, and provide aural and visual warnings to the flight crew when an unsafe proximity to terrain or obstacles is detected. The category includes Ground Proximity Warning Systems (GPWS), Enhanced Ground Proximity Warning Systems (EGPWS), and Terrain Awareness and Warning Systems (TAWS).
Plain English
Equipment in the cockpit that watches how close the aircraft is getting to the ground or to high terrain, and warns the pilot before it becomes dangerous.
Context Anchor
Seen in instrument flying, especially when discussing controlled flight into terrain prevention, glass cockpit alerts, and approach or departure safety.
Derivation
Terrain comes from the Latin terra, meaning 'earth' or 'ground.' Alerting comes from the Italian all'erta, meaning 'on the watch.' Together the name describes a system that keeps watch on the ground below and ahead of the aircraft.
Why Pilots Care
These systems help prevent controlled flight into terrain accidents, the leading cause of fatal general aviation crashes in instrument conditions.
Grounding Statement
If the aircraft is descending toward a ridge hidden by clouds, a terrain alerting system may warn the pilot before the ridge is visible.
Intuition Check
Do not assume a terrain alerting system flies the airplane away from danger. It warns the pilot; the pilot still has to understand the alert and take the correct action.
Example Sentence 1
During the night approach into mountainous terrain, the crew briefed the response procedure in case the terrain alerting system issued a warning.
Example Sentence 2
Before departure the pilot reviewed the terrain alerting system database coverage for the planned route over mountainous areas.