An interesting read, especially how both aircraft determine (and communicate) if they are in the air. That, coupled with the decision thresholds and hysteresis present in all of the relevant systems, leads to an interesting set of circumstance where the information being presented (or not, as the case may be) to controllers has a non-zero probability of being very wrong.

If the 777 pilots had not followed procedure, this could of gone another way. But they did and now we get to read about an incident, not an accident.