ROCHESTER, N.Y. — A pilot’s inattention and failure to follow safety rules likely caused a commuter plane in February to plummet from the sky near Buffalo, killing 50 people, the airline told federal investigators.

The twin-engine turboprop also lacked an adequate system to warn the pilots when the plane was flying too slowly, contributing to the tragedy, said Colgan Air Inc.

“The probable cause of the accident was the flight crew’s loss of situational awareness and failure to follow Colgan Air training and procedures, which led to a loss of control of the aircraft,” Colgan Air said in a Dec. 7 report to the National Transportation Safety Board.

The Air Line Pilots Association counters that a combination of factors other than pilot error caused the crash. In a report also sent to the safety board last week, the union argued that Colgan Air failed to adequately prepare the pilots for the wet, freezing conditions they faced on the night of Feb. 12.

The Manassas, Va., regional airline operated the flight for Continental Airlines Inc. and is facing lawsuits related to the crash.

Continental Connection Flight 3407 went into an aerodynamic stall and spun out of control as it approached Buffalo Niagara International Airport, slamming into a house and bursting into flame. All 49 aboard and one man in the house died.

The NTSB’s report on the crash is expected to be released by early February. Its investigation has spotlighted the long hours, low pay and long-distance commutes of regional airline pilots.

The agency exposed a series of critical errors by the turboprop’s captain, Marvin Renslow, and co-pilot Rebecca Shaw just before the crash.

It’s not clear where Renslow, of Lutz, Fla., slept the night before the accident, but it appears he may have tried to nap in a busy airport crew room where Colgan Air kept bright lights on to discourage extended sleeping. The first officer commuted overnight from her home near Seattle to Newark, N.J., to make the flight to Buffalo.