I want to know about the Details of Enhanced ground proximity warning system or(EGPWS). Now it's Manadatory Device from 01 Feb 2005. Why it is so required in flight? Please reply me briefly.

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Zahiruddin Md. Imrul Quayes
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All aviation mishap categories have gone down EXCEPT "controlled flight into terrain". Radar, air traffic controllers, transponders, mode C transponders, TCAS and other systems prevent collisions with other aircraft, but they do not prevent collisions with the terrain. An EGPWS does that. Or tries to.

EGPWS provides pilots with situation awareness in a graphic map-like format when descending into airports surrounded by high terrain. Unlike the old dumb GPWS which reacts at the last moment and gives no clear indication which way to turn to get out of trouble, EGPWS gives an almost preventative picture of potential problems before it's too late.

There was the case of an American Airlines 727 which descended to the runway at Chicago O'hare in 1993 with it's wheels up. because the old Sunstrand GPWS did not perceive the wheels up as a descent to land, it did not give the appropriate warning and the 727 scraped it's belly along the runway, struggled back to altitude and finally made a safe landing. GPWS also failed to warn pilots in a 1995 CFIT crash of a Dash 8 in NZ for similar reasons. (ie wheels up)

If you want to understand what happened, download the tape.