TIS is sporadic/hit miss. With altitudes as low as the Hudson river and the PHX choppers, you routinely hear the lady's "TIS not available" as you go below coverage altitude for where your aircraft is.
The PHX choppers are an exception because both pilots were flying and reporting what they were seeing which means much less room to look for another chopper. The Hudson river one was terrible, and I don't know if they proved that TIS indeed was working and showed them the yellow dot on their screen.
Which was indeed a problem in the PHX accident, that of both pilots being "pilot/reporters", ie- distracted with doing the live news reports while still being the only pilot onboard. The other crewman in both helos was a cameraman filming, so essentially, no one was looking outside for other traffic, all eyes were at the ground at the police situation going on.
A very specific set of dynamics indeed, but one where even a traffic awareness device such as TIS was no guarantee of protection, due to its own inherent sensor limitations, especially for rotary wing. And this was in addition to the fact that the two helicopters were talking to one another on helo common freq.
In the Hudson accident, it was known that TIS info was being received; it's now known what each pilot had displayed though.
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