Although it has been technologically possible for some years to give warning of ground collision hazards, the specialized radars for this purpose have been limited to military aircraft. Because of complex cost and installation problems, radar of this type have not been installed in civil aircraft.

This paper discusses possible developments in civil weather radar to enable it to give a warning of ground collision hazards. The paper was presented at an Ordinary Meeting of the Institute held in London on 19 November 1969 with the President in the Chair.

For the purpose of this paper, ground collision is defined as an error of navigation or height management, which results in a zero ground clearance. The error can, of course, be human or instrumental but the assumption is made that the aircraft was basically capable of avoiding the hazard. There has been a tendency to associate ground collisions, particularly hill and mountain collisions, with the older piston-engined aircraft. Its importance in terms of airlines operating modern jet aircraft is not always well appreciated. It is true that the normal operating altitude of jet aircraft almost eliminates ground collision hazards in the cruise phase, but in general they suffer from a longer response time and a higher approach speed, which makes them more vulnerable in the let-down and approach phase. Since in any event the let-down and approach phase accounted for about two-thirds of the accidents with piston-engined aircraft, ground collision hazards remain a serious problem with pure jet aircraft.