Squibbler
One should not land before any runway threshold - period ... but I am interested in why you quote PAPIs in this instance.
If a light single under VFR is making a typical 5-6 degree approach, they are surely irrelavent?
3 degrees works well with heavy metal speeds (and redundant power), but is rather on the shallow side for a light single, especially if there is obstruction creating a displaced threshold ... e.g. for a PA28-161 (source OATS expanded checklist) at vref +5 (70 kias) the profile would be circa 300' per NM.
Therefore an engine failure at say 1.5 miles out would not allow many options. 450 feet of energy wouldn't make the runway (best glide 75 kias, sink rate say 600 fpm = 480' per NM - if the pilot was very accurate and quick to react)and the best option may be very unpalatable.
Do many experienced PPLs fly the PAPIs with a in your experience?
Apologies to all for wandering off thread, but this matter does intrigue me.