All aboard the ill-fated jet perished. Military jets reported seeing the windows fogged up while the plane was still in flight, which could suggest the loss of cabin pressure, as well as the loss of enough oxygen to cause unconsciousness. Though emergency oxygen was available, in older planes it had to be activated manually by the crew.
Oxygen deprivation causes many pilots to behave irrationally, meaning that in the minute or two they need to adjust controls, many do make wrong decisions.
An emergency oxygen tank was found empty, but officials could not determine if the tank was empty before the flight began. Pressure problems were reported with the Learjet prior to the flight, but it was impossible to tell if maintenance done on these systems was done correctly.
The plane did have a so-called 'black box' to record the plane's instruments at the time of the accident, and the 30-minute voice recorder recycled itself during the four-hour flight.