What is the difference between a PAPI and an APAPI?
And similarly, the difference between a VASI and a T-VASI.
I know a PAPI is a more advanced and more accurate development of the VASI system - does anyone know what year each system was introduced?
Also how does a PLASI unit have both flashing and steady lights visible, depending on the glidescope?
Hadn't heard of the PLASI before this evening - is it used much?