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.

During a Sunday briefing, Chealander described the flight’s frantic last moments, which included a steep drop and roller-coaster-like pitching and rolling.

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. Passengers and crew would have experienced G-forces up to twice as strong as on the ground.

The plane crashed belly first onto a house Thursday night, killing all 49 people on board and one person on the ground.

Just before they went down in a suburban neighborhood near the Buffalo airport, the pilots discussed “significant” ice buildup on their wings and windshield. Other aircraft in the area told air traffic controllers they also experienced icing around the same time.

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, a condition called a stall.

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 deicing 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.

He said the pilot was being “very conservative” by turning it on so soon.

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

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.

Still, Chealander was careful not to criticize the pilot.

“Everything that should have been done was done so we keep looking,” he said. “We keep looking, trying to find out why this happened.”

Colgan Air operates a fleet of 51 regional turboprops for Continental Connection, United Express and US Airways Express.