The first generation of those systems was known as a ground proximity warning system (GPWS), which used a radar altimeter to assist in calculating terrain closure rates. That system was further improved with the addition of a GPS terrain database and is now known as an enhanced ground proximity warning system (EGPWS). When combined with mandatory pilot simulator training which emphasizes proper responses to any caution or warning event, the system has proved very effective in preventing further CFIT accidents.[8]