anyone know why NAT track altitudes are opposite to normal direction of flight altitudes? Today I'm westbound on NAT A and valid altitudes for the track are 35,37 and 39 -- all normally eastbound altitudes
The real reason behind it is traffic load. The majority of traffic across the Atlantic happens in two waves, eastbound in the evening hours for North America, and westbound in North America's morning/afternoon.
The volume of traffic going in one direction is so great that the tracks are not able to handle the volume of traffic unless addition altitudes are given to the tracks, even wrong way altitudes. Since there is so little counter-direction traffic, this makes more efficient use of airspace that would otherwise be vacant.
