BOAC do you understand the difference between what a T-VASIS tells you and a PAPI? One is angle of decent, the other is decent path to varying TCH based on cockpit eye position. Flying 2 reds 2 whites on a PAPI maintains a descent angle to the PAPI, good luck calculating TCH. Flying any other combination leads you to the same point at a different angle. Flying different lights on the T-Vasis maintains the same glide slope angle but adjusts the TCH, a very easy calculation. You just have to adjust for eye-position or cockpit level something manufacturers can do easily. Wouldn't it be great to come out the bottom of an ILS and say 1 dot low thats what i expected rather than its all red lets fly up to the PAPI.