The Embraer had submitted a computer-generated flight plan to Air Traffic Control for the run north to Manaus. This was for a routing that would take N600XL over Brasília, where, after a slight left turn, airway UZ6 would lead the airplane 1,200 miles to Manaus. It passes over Caiapó Indian territory and Fazenda Jarinã. On the basis of forecasted winds and the Legacy’s performance, it requested a climb to 37,000 feet, or flight level 370, an altitude appropriate for the initial direction of flight. Until Brasília, that direction was slightly to the east side of magnetic north. Airplanes cruising on such easterly headings are usually assigned “odd” altitudes (35,000, 37,000, 39,000), while airplanes cruising on westerly headings are given “even” altitudes (36,000, 38,000, 40,000). Virtuoso air-traffic controllers sometimes allow exceptions to be made when traffic is light (and exceptions are systemic along certain one-way routes), but these cruising rules dictate the altitudes at which airplanes fly worldwide. Since the airway to Manaus required a westerly turn over Brasília, the computer proposed a descent to 36,000.