Originally Posted by 321XLR/FAA AIM
a PAPI provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 3.4 NM from the runway threshold.
I suspect that means OUT TO. All the action happens approaching and under 1000ft so it would be pretty pointless having a system that is only supposed to be used outside 3.4nm. And they are certainly useable close-in. A quick glance when over the threshold would tell me if Bloggs was going to land long.
