OK OK thanks for the inputs so far everyone.
I didn't want this thread to turn in to a PAPI vs T-VASIS debate but there you go it's happened.
For what it's worth I personally believe that the T-VASIS is superior to the PAPI because as has already been pointed out there is no colour perception required (which also eliminates the problem when the lights are dimmed for night operations), there can be multiple aiming points so that each set up can accommodate many different types of aircraft, and if you do see red lights? for goodness sake hit the TO/GA switch because you are about to hit mother earth!
For those of you who don't understand how T-VASIS works you can think of it this way (although it is not strictly correct but the concept works very well). Think of the four horizontal lights as the centre (and most commonly used) aiming point which is usually at the 1000' markers at an angle of 3 degrees.
If you see a lights sticking out closer or further down the runway than those four horizontal white lights (that appear from your perspective to be below or above the four horizontal lights), that simply means that if you were to fly a 3 degree path from your current position to the runway, your eyes will meet the runway abeam that light which sticks out the most. So if the dots appear to make a T, a three degree path from your present position will have you arriving abeam the bottom of the T. The longer the T is (one, two, or three lights), the further short of the 1000' aiming point you will land. If you see an inverted T, a 3 degree path from your present position will have you landing beyond the 1000' aiming point abeam the top of the inverted T. No thinking required.
But any way I am resigned to the fact that PAPI seem to be cheaper to own and operate and that they comply with the minimum specifications required. I just think that they can (and should) be improved with the use of xenon bulbs.
So I've gota ask, how many pilots does it take to change a light bulb?
