A question about the dynamics of this incident, which shows something I've never experienced, but I haven't flown in all ATC jurisdictions.
Incident: Wizz A320 near Madrid on Nov 10th 2018, descent below cleared level causes near collision
Incident begins with two aircraft straight and level -
westbound - at FL310 and FL290. Usually I'd expect westbound aircraft to be at "even" flight levels 280, 300, or 320, for example. Although the primary rule in Class A is "what ATC assigns," of course.
Is this just because the aircraft are closing on 110nm to destination and for ATC purposes are in a preliminary descent? Would the RVSM floor of FL290 be a factor (as low as possible while still allowing RVSM-rules flexibility, regardless of direction)?