Quote Originally Posted by Mike View Post
As Oblivian wrote, the data need to be requested from a ground station. More information about Extended ModeS in this blog post
https://www.flightradar24.com/blog/u...flightradar24/
Yes it seems that an ATC ground station has to initiate the extended reporting, but from the mixed returns over the US seaboard, it also stays on unless told to stop. That would explain why aircraft into the US displayed it, but not outbound.

Reception of Extended Mode S data also requires that the air navigation service provider where the flight is operating is interrogating the aircraft’s transponder to request the data. While this is increasingly common, it is not yet universal.