Having watched the video and read the report I agree with the comment made in the video - before this incident some “pilots” assumed the ILS was always accurate unless otherwise flagged. Therefore, despite the NOTAM, this crew assumed that because it appeared the glide slope had been captured, it had been captured. The doubts came from the unusual pitch change and the external visual clues, not the DME, but were in them selves not sufficient to provoke the crew to react immediately to the lack of correlation in the information available to them because they were convinced they had captured the glide slope, which, in their experience was “infallible”.
DFC suggests that what is to be learnt is the importance of cross checks - never relying on a single instrument. He is clearly correct.
I0540 suggests a moving map GPS may have helped. In this instance the primary cross check had to be of range. Whilst this information may have been provided by almost any GPS, in many cases would the information be presented clearly, and notwithstanding the integrity of the GPS, would the range be the required range? For example, the range might be that to the center of the airport not the threshold. In other words if the pilot were cross checking with his GPS in the “amateur” world of GA would he necessarily know precisely what the GPS was telling him? The aircrafts position on the moving map would have been of little help.
In this particular case the correlation between the glide slope and the DME provides the best instrument clues that something is wrong and in themselves are sufficient to provoke the procedure to be aborted.
It is of course suggested that the localiser can never be susceptible to this type of error. Does that mean the localiser can be relied upon without any other cross checks? Is there any scenario in which the localiser might provide incorrect information without the crew being given adequate warning? In this instance a cross check with a moving map would provoke similiar concern that all was not well. If it did, and the moving map GPS happened to be one of DFCs three and six boxes on which would you rely?
In light aircraft I am becoming a great devotee of the G1000 displays. However, even with these displays this emphasises the importance of understanding the information with which you are provided, and the source from which the systems are deriving the information.