Originally Posted by Le Pingouin
The "entire separation schemes, fuel cost savings from reduced separations, direct routings, etc., etc" doesn't break down if there is an aircraft with broken ADS-B. We just have to resort to using procedural separation between that aircraft and any others it crosses paths with. A 1000ft works quite well.
I don't think Sunfish was talking about broken ADS-B insofar as failure to transmit data to ATC, so much as transmitting
bad data to ATC who has no way to prove if the displayed return is actually where the system says he is.
Given that the majority of navigation these days is by GPS, it can reasonably be assumed that the navigation source is the ADS-B source, however this is not always the case, particularly as the 'all IFR traffic' mandate approaches. It is quite possible to have one GPS driving the needles with another telling ATC where you are. If they disagree, which is trustworthy, and how does ATC know?
For systems that are supposedly "failsafe" in such a critical role, I would really like more security in a technology that can easily be spoofed or jammed.