Federal investigators have determined that the plane flown by Russ Francis and another man crashed because of an apparent engine failure, the Associated Press reports.
The former NFL tight end, who was 70, and co-pilot Richard McSpadden, 63, died in the crash at Lake Placid Airport on Sunday afternoon.
The single-engine Cessna 177 turned around in an attempt to land after declaring an emergency shortly after takeoff.
National Transportation Safety Board investigator Todd Gunther told the Adirondack Daily Enterprise that the plane hit a berm at the end of the runway and fell about 30 feet into a ravine.
Francis was a veteran pilot who was the president of Lake Placid Airways, which runs charter and scenic flights. McSpadden is Aircraft Owners and Pilots Association senior vice president.
The Patriots made Francis a first-round pick in 1975 out of Oregon. He made three Pro Bowls and earned two second-team All-Pro selections with New England before retiring after the 1980 season. He returned to play in 1982 and was traded to San Francisco, where he spent six seasons and won a Super Bowl.
Francis ended his career by returning to New England after being waived in 1987, and he played his final 12 games for the Patriots in 1988.
Francis made 393 catches for 5,262 yards and 40 touchdowns in his career. He ranks 21st all-time in catches and 16th in receiving yards for the Patriots and 30th and 32nd in the same categories for the 49ers.
