Just to clear something up Sandal boy
; from the report:
1.6.10 The aircraft was equipped and approved for single-pilot IFR operations. Standard flight instruments were fitted to both the pilot and co-pilot panels. Avionics items were Bendix or King equipment, and consisted of 3 very high frequency (VHF) communications radios, 2 VHF navigation receivers (NAV 1 and 2), marker beacon receiver, one distance measuring equipment (DME) system, 2 automatic direction finder (ADF) receivers, audio and intercom systems, one radio altimeter, one global positioning system (GPS) and one ELT. VHF navigation information was presented to the pilot on a horizontal situation indicator (HSI), by a flight director on the attitude director indicator, and by a secondary course deviation indicator (CDI). ADF or VOR bearings were presented on a radio magnetic indicator (RMI). A Bendix Altimatic V autopilot was fitted, with altitude hold, heading, navigation, approach and go-around modes available. The pilot also had a portable Garmin Pilot III GPS mounted on the instrument panel.
Unlikely that by monitoring GPS distance you would get low because unless he had put in a user defined waypoint on the threshold of runway 20, then the active waypoint would most likely have been CH, i.e. the co-located VOR and DME. This would give you almost identical distance information (slant range not an issue at low level). It is conceivable he had the aerodrome reference point (NZCH) as the active waypoint and was using distance information from that, but that would make him an idiot.
If you have any doubt about the lunacy of doing approaches using user defined waypoints, take a gander at this little ripper.
(You might have to sign up to the free site).
http://www.flightsafety.org/members/.../ap_june02.pdf