I cut my Ops teeth out on the airfield at Heathrow, over 25 years ago. At that time, we had VASIS installed on 5 out of 6 approaches. We had a weekly routine with the engineers, calibrating each box of each set. This took a crew of 5 or 6 people a complete morning. The results were less than satisfactory from an accuracy point of view; the first 747 movement would blast the boxes and we'd have to go and check them again, if anyone complained. Far from satisfactory! In the early eighties, a PAPI replacement programme was started. The units are much more blast-proof and stay in calibration very well. We also had mega problems with pink emissions from the units and went to 30 min warm-up periods then eventually permanent heaters being fitted to alleviate this problem. The units now are very reliable and accurate and I for one wouldn't DREAM of going back to VASIS.
You pilots want us Ops types to give you the best, most reliable, fail-safe aids that we can. It isn't just a money thing- from my point of view anyway.
The only downside for me with PAPI is the aforementioned business with B747 eye-height; it does mean that everyone else touches further down the runway than necessary. I've advocated a 5-light setup in the past, so you can choose a nearer or further aiming point, but someone's bound to choose the wrong one!
Incidentally, each 'light' consists of several lamps so that some lamp failures can occur but the system remains usable - not always the case with VASI.
Stick with it - it's worth the hassle!
Cheers,
The Odd One