There is no mention of the possibility of erroneous light signals displayed by the PAPI under the high moisture conditions described in the report. This is a well known phenomena in all types of VASIS particularly those visual systems that use colour coded displays. There is a strong suspicion in some circles that a fatal accident to a RFDS aircraft flown as single pilot, may have been caused by the pilot following erroneous fly-down light signals, during a dark night poor visibility approach into Mount Gambier. That aircraft - a Kingair 200 was flown by a 13,000 pilot highly experienced in black hole approaches.
Later, ERSA was amended to warn pilots of erroneous T-VASIS indications that could occur under certain weather conditions at Mt Gambier.
In the Christchurch case, although it appears that the pilot's flying was sloppy on the ILS glide path, there is significantly no discussion on whether he may have seen the PAPI approaching the ILS minima and attempted to follow its indications.
There is no proof - -only supposition - that the pilot did not become partially visual with the runway in the last few seconds of the flight. Conditions were ideal for erroneous VASIS light signals - there is plenty of documented evidence of this shortcoming in VASIS/PAPI design. Low fog amd mist over the VASIS can cause significant light bending resulting in erroneous signals as seen by the pilot.
The magazine Australian Aviation recently ran an excellent and thought provoking article on VASIS errors in high moisture laden air conditions. Virtually, one cannot trust what one sees just when you need to rely on the system for safe glide path guidance.
Certainly in the ATSB report of the Mount Gambier night accident where the Kingair flew into the deck in line with the runway and 3.1 miles from the threshold, there was no mention at all of the possibility of erroneous VASIS light signals in foggy conditions. Simply, the investigators didn't think of it unti lafter the report was published after local pilots described the Mt Gambier VASIS as well known unreliable in fog and mist - exactly the same as the Christchurch weather.