A UPS cargo plane that crashed on Thursday near the Birmingham, Alabama airport is being inspected by the National Transportation Safety Board. The NTSB has released some information on possible causes of the crash and its victims.

The Airbus A300 had two pilots: 58-year-old Captain Cerea Beal, Jr., and 37-year-old First Officer Shanda Fanning. Both died in the crash, which would have completed their third flight of the night. Investigators are looking into the possibility that fatigue was a factor; the pilots began their night at 9:30 PM in Illinois, flew to Kentucky where they may have used rest rooms, and crashed shortly before 5 AM, writes Bloomberg.

At least one fail-safe intended to warn air traffic controllers that the plane was flying didn’t work, while at least one cockpit warning—a recording of the words “sink rate” 7 seconds before the crash—did. The plane, which crashed within 5,280 miles of the landing strip, was scheduled to land on a strip 5,000 feet shorter than the runway normally used, and lacking in an instrument landing system to help pilots. Investigators found no apparent problems with the engine or controls, and the plane was traveling the expected 161 mph at the time of the crash, according to Fox News.