Originally Posted by
Katamarino
It seems to me that, as used by ATC today, Mode-S offers absolutely no advantage over Mode-C to us GA pilots - am I missing something?
Mode-S elementary (i.e. what we use) offers very little observable benefit to anyone vs. Mode C.
There is fact that Mode-S transponders reply less frequently than Mode -A/C when interrogated by an ACAS system or by compatible ground radar. This has reduces the RF traffic on the transponder frequency, and has a potential benefit that the level of interference on the transponder frequency would become a problem with the increasing use of transponders and ACAS.
There are some potential benefits (over the horizon at the moment) like replacing the squawk code with the aircraft identifier (helping to relieve the European shortage of codes) and support for ADS-B.
In the LTMA they have a nice tool to show the vertical profile of a stack (who is where) in addition to the traditional overlay of all of the targets in the stack painted on top of each other. It maybe Mode-S elementary transponders work in this environment (but it is unlikely that a PA28R is going to be in the LAM Stack!)
Mode-S enhanced does offer some advantages to ATC to help avoid level busts and communication errors (like a different speed or heading being selected vs cleared)