In response to the comments by
SixDelta, I was nearly going to say that there are some places around the world where ILS alarms are not always all that they should be. Of course, in such places, the calibration of a PAPI, VASI or VASIS would probably be even more suspect!
However, I find myself in general agreement with the concept of using the ILS GS for guidance in preference to a PAPI/VASI/etc. Having been extensively involved in calibration (in a previous life), I can tell you that harmonisation of a PAPI (etc) with an ILS GS isn't always highly successful.
