Sir - You published a letter of mine in November 1990, which proposed a system of radar surveillance to give visual warning of glideslope deviation on the controller's display, so that the controller could query the deviation with the aircraft concerned.
A second (unpublished) letter expanded this concept to include the terminal manoeuvring area and minimum safe-altitude data.
It is interesting to read that such a system was operating at the time of the recent Guam disaster, but, sadly, a software error suppressed the warning which could have saved so many lives at this time.
Peter Fitzwater
Ascot, Berkshire, UK
Source: Flight International
