How to understand that an aircraft is landing or taking off by analyzing MSG messages? According to this article we just need read GND field (22). I also heard that during landing the aircraft is sending MSG.2 with field 22 at 1.
I don't understand whether the aircraft is landing or taking off when the field is 1. It seems it just means the aircraft is on the ground, but there is no information about it's exact state.
How to actually detect that an aircraft is landing or taking off?