EGPWS – is a GPS based Ground Proximity Warning System that alerts the A/c of a dangerous proximity to ground closure.
The system has a digitalized information of topographical map of the Earth’s Terrain fed in its database and this is constantly compared with the A/c flying over the ground, calculated by the GPS based position to alert the A/c if it is dangerously close to a terrain or an obstacle.
The visual as well as Aural alert is presented on a EFIS system.
It is a requirement by regulations to install EGPWS on all A/c having an All Up Weight more than 15,000 kg Or seating capacity more than 30 passengers.
The indications for the terrain clearance is as follows
Green– Clear Terrain. Terrain poses no threat to the A/c.
Yellow– Hazardous Terrain. Terrain is at or above the A/c altitude but is not on the flight path of the A/c path.
Red- Hazardous Terrain. Terrain is at or above the A/c altitude en route the flight path and is a significant threat to the A/c.
The Pilot has the authority to deny any ATC clearances like Radar Vectoring etc, if he feels that it will cause him to be in proximity to a Yellow or Red display to the Terrain in the cockpit as a dangerous situational awareness.
The EGPWS causes a Caution alert to be active Approximately one minute before the A/c enters the potential collision area, considering the A/c performance as it would have performed in the worst case scenario.
If A/c is flying too close to the terrain or an obstacle the EGPWS will provide a Caution Aural alert in the cockpit.
If A/c still continues to be in dangerously close proximity to a obstacle or a terrain the system will issue a Warning Aural alert in the cockpit, along with a safe maneuver guidance on the Flight Director bar to clear the obstacle which is only in vertical guidance.
Peak Mode – is a mode in which an A/c flying at any altitude can have a look at the information of the surrounding terrain in the operating area to increase situational awareness and is very useful in the case of a emergency.
Example – As in the case of an engine failure and diverting to a nearby airfield, flying in the mountainous regions.
The standard practice requires that any time the EGPWS warning Aural alert comes in the cockpit, the Pilot should immediately level the wings and increase full throttle to initiate a climb maneuver at a nose up of about 20° above the horizon.