I will not deny that the system could have been designed better but unfortunately without a major overhaul to exisiting system that would leave a lot of GNSS units incompatible with a new RNAV design we will no doubt be stuck with what we have for quite sometime to come.
Different TSOs and different manufacturers programming of their units result in them behaving one way or another. One example is a TSO-129 GNS430 will scale to CDI of 0.3 at the FAF, whereas a TSO-146 version of the same model will scale to 0.3 by the FAF and continue to reduce to a scale of 0.1 by the MAPT.
I will not defend the approach design we have for RNAVs, yes it could be better, maybe it was deemed to hard at the initial design phase of the TSO for the first GNSS that were to be RNAV capable to programme it differently and this has cascaded on to later designs, but at the end of the day a computer can be programmed to behave any way it is desired.
Another trap that have resulted from the waypoint designs is the failing of some people to compute in their minds that just because they are within 10/25nm of the IAF that they are tracking to does not necessarily mean they are within the 10/25nm MSA, however that is more so a situational awareness issue.
I suppose one benefit there has been from a FAF waypoint is to provide an easy direct to point for tracking to a 5 mile final when you are not conducting a RNAV approach, but yes, it wasn't designed for that and the potential for error that that waypoint provides whilst conducting an approach in trying conditions far outways the abovementioned benefit.
Last edited by Check_Thrust; 24th Aug 2013 at 11:06.