On Tue, 21 Aug 2007 11:15:13 +0000, Larry Dighera wrote:

Doesn't it make more sense to have a few ground-based radar installations
for traffic separation rather than the hundreds of thousands of ADS/B
installations for it to work?

How would a few ground-based installations cover the entire nation? Or
are you speaking only of the LA area?

One advantage of ADS-B is that properly equiped aircraft can "see" each
other even outside of RADAR coverage. Being in RADAR coverage provides
additional "service" (more information is spread more widely), but the
system doesn't *require* that coverage to function.

However, outside of RADAR coverage full (and mutually compatible!) ADS-B
ubiquity is necessary. And since, at least last time I checked, ADS-B has
at least two (three?) mutually incompatible transceivers, even achieving
100% installation wouldn't be enough.

My opinion is that this is a good idea but (1) it'll take some time for
the full utility to be achieved and (2) it'll be completely screwed if the
compatibility issue is left unresolved.

As far as the GPS requirement, this is a separate issue. "Modern"
navigation devices should exploit a combination of space and ground based
systems. Why we have "GPS units" rather than more diverse "Navigation
units" is probably just a matter of cost. But, obviously, there's yet to
be much in the way of a call for these superior "Navigation units".

Perhaps I'm wrong, though. Perhaps it isn't cost, but the expectation
that ground based navaids are really going to be shut down. That would be
bad.

- Andrew