BUFFALO, N.Y. — The commuter plane that crashed near Buffalo was on autopilot until just before it went down in icy weather, indicating that the pilot may have ignored federal safety recommendations and violated the airline’s own policy for flying in such conditions, an investigator said Sunday.

Federal guidelines and the airline’s own instructions suggest a pilot should not engage the autopilot when flying through ice. If the ice is severe, the company that operated Continental Flight 3407 requires pilots to shut off the autopilot.

“You may be able in a manual mode to sense something sooner than the autopilot can sense it,” said Steve Chealander of the National Transportation Safety Board, which also recommends that pilots disengage the autopilot in icy conditions.

Automatic safety devices returned the aircraft to manual control just before it fell from the sky, Chealander said.

Chealander said information from the plane’s flight data recorder indicates that the plane pitched up at an angle of 31 degrees, then pitched down at 45 degrees.

The plane rolled to the left at 46 degrees, then snapped back to the right at 105 degrees — 15 degrees beyond vertical.

Radar data shows Flight 3407 fell from 1,800 feet above sea level to 1,000 feet in five seconds, he said.

The plane crashed belly first onto a house Thursday night, killing all 49 people on board and one person on the ground. The flight’s first officer, 24-year-old Rebecca Shaw, was from Maple Valley and a Central Washington University graduate.

Just before they went down in a suburban neighborhood near the Buffalo airport, the pilots discussed “significant” ice buildup on their wings and windshield.

The Dash 8 Q400 plane operated by Colgan Air was equipped with a “stick shaker” mechanism that rattles the yoke to warn the pilot if the plane is about to lose aerodynamic lift.

When the stick shaker engaged, it would have automatically turned off the autopilot, Chealander said. Before that, the pilot switched on an anti-stall device that increases the speed of the plane by 20 knots and gives a pilot more margin to recover from a stall if it occurs.

Chealander said the plane’s de-icing system was turned on 11 minutes after it took off from Newark, N.J., and stayed on for the entire flight. Indicator lights showed the system appeared to be working.

Investigators who examined both engines said they appeared to be running normally at the time of the crash.

In a December safety alert issued by the NTSB, the agency said pilots in icy conditions should turn off or limit the use of the autopilot to better “feel” changes in the handling qualities of the airplane.

Federal Aviation Administration spokeswoman Laura Brown said the agency advises pilots to disengage the autopilot when ice is accumulating, but the guidance is not mandatory.

She also said some planes are certified to be flown on autopilot in icing conditions because doing so “may actually keep the aircraft at a steadier speed and altitude than a pilot could flying it manually.”

Brown did not know if the 74-seat Q400 Bombardier aircraft was certified to be on autopilot during icing conditions.