The cockpit instruments were old ... Mexican aviation regulator DGAC did not seek background information on the Learjet 25 co-pilot, saying he was inexperienced and lacked the U.S. certification ...

Cockpit voice recorder of the Learjet 55 that crashed on January 31 in Philadelphia. [Credit: National Transportation Safety Board] NTSB said it also recovered the aircraft’s enhanced ground ...

which might provide clues as to what was happening in the cockpit during the crash. The Learjet did have such a recorder, though it was an older, tape-based model. (Newer ones are solid-state ...

A cockpit voice recorder was not functioning ... And while the doomed Learjet 55 was in contact with an air traffic control tower, "there were no distress calls received from the flight crew ...