what follows is something quoting an article in a south american newspaper...if true, it makes some sense
also, being granted such a large altitude for enroute is sometimes known as a "bock altitude" clearance. ie: maintain block Fl350-FL390.
read on.
ouch if true:
Rio de Janeiro - A lack of dialogue between two control towers was likely to blame for Brazil's worst ever plane crash last week in which 155 people died, the Brazilian daily O Globo reported Monday.
The mid-air collision between a Boeing 737-800 and a smaller twin- engine plane occurred because both machines flew into a so-called border region in the state of Para which was jointly controlled by two towers, O Globo reported citing an anonymous official in Brazilian air traffic control.
The two control towers did not speak to each other about the planes entering the same airspace and offered similar flight altitudes to their respective planes, thereby causing the crash, according to the report.
The US pilot of the smaller Embraer Legacy plane managed to make an emergency landing at a military landing site in Para.
Rescuers said there was no hope of finding survivors as they began the arduous task of removing bodies from the crash site of the Boeing plane, whose wreckage was discovered early Saturday in a remote, heavily forested area of the Amazon.
Brazilian President Luis Inacio Lula da Silva called for three days of mourning Saturday.
Air traffic control in Manaus allegedly suggested the Boeing maintain a flight altitude of between 35,000 and 39,000 feet, while the tower in Brasilia recommended an altitude of 37,000 feet for the Embraer Legacy flying in the opposite direction.
A full investigation into the cause of the accident would take about three months, given the difficulty of reaching the crash site, the authorities said.
The worst previous aviation accident in Brazil was in June, 1982, when a Boeing-727 of the Vasp airline crashed into a mountain in the north-eastern state of Ceara, killing all 137 people on board.