[Ref ACE The Technical Pilot Interview 152/348]

The GPWS (Ground proximity warning system) is mandatory required for public transport aircraft over 5700 kg. It is a important system provide two major functions: 1) alert and 2) warning system.

After reaching certain precomputerized active range, a central computer will then activate aural and visual alerts to warn the flight crew by using the following cockpit equipment:

1. Speakers – “Pull Up“
2. a pair of red warning lights with “Pull Up.”
3. inhibited amber (marker) advisory light (in a glide slope deviation)

The GPWS receives various data inputs (configuration, height/ altitude, and check if there is instrument landing system (ILS) glide slope deviation). It then calculates these inputs to detect if any of the potential dangerous:

1. Excessive descent rate
2. terrain closure
3. Height loss after takeoff
4. Flaps or gear not selected for landing
5. Too low on the ILS glide slope
6. Descending below approach minima

When (if) more than one alert or warning is triggered at the same time, the GPWS will give only the highest-priority alert or warning that has been triggered.