Federal investigators probing the crash of Continental Connection Flight 3407 are focusing on possible pilot error -- both before and after the plane lost control and crashed into a home in Clarence Center last Thursday night, killing 50 people.

The National Transportation Safety Board confirmed Wednesday that investigators are looking into whether the plane's autopilot was programmed correctly before the plane lost control. Other sources said investigators question whether the pilot later mishandled his attempt to right the plane's course.

Federal officials caution that it is far too soon to determine any blame in the accident, and independent aviation experts cast doubt on whether any pilot could have saved the plane once it spun out of control at the relatively low altitude.

But sources said it is possible that fatal mistakes were made.

Asked if the pilot had been operating the autopilot in the improper mode, NTSB spokesman Keith Holloway said: "We haven't definitely determined that yet. But that discussion has come up."

The NTSB and the Federal Aviation Administration disagree on the use of autopilot during the sort of icy conditions that occurred the night of the crash, with the safety agency urging pilots to refrain from its use in the worst winter weather.

But the concern raised Wednesday about how the autopilot was operated is a separate issue -- and one that has come up again and again in other accident and incident investigations.

A law textbook called "Aircraft Accident Reconstruction and Investigation" lists 14 incidents in which the autopilot was wrongly used or improperly monitored. In one case, the plane overshot the runway and two people were killed. In another, the pilot programmed the wrong speed into the system, prompting a fatal crash.

Many planes have several different autopilot modes, and the mode the pilot chooses and how he or she programs the device is hugely important, aviation experts said.

"It can make all the difference in the world," said M.P. Papadakis, a retired airline pilot with 23,500 flight hours and a lawyer who wrote the textbook chapter that details improper use of the autopilot.

However, it is difficult to know exactly what might have happened on Flight 3407 without details of that aircraft's autopilot system, Papadakis added. The plane's manufacturer, Bombardier, did not respond to a request for a description of the plane's autopilot system.

Investigators are looking not only into the use of the autopilot system, but also into the actions of the plane's crew once the autopilot was shut off and the plane lost control.

Sources familiar with the investigation said that as the plane descended, an automatic stall warning sounded. According to a computerized re-creation of the flight's final seconds, that could have prompted the pilot to add power to try to raise the plane's nose.

The trouble is, the proper procedure would have been to push the plane's nose lower to increase the speed. But by trying to raise the plane's nose and holding the controls there, the pilot might have ensured that the plane's speed slowed to the point where it experienced an aerodynamic stall.

The Wall Street Journal first reported that scenario Tuesday.

"They said that we're looking at the pilot's actions, and it's one of many things we're looking at," said NTSB spokesman Terry Williams. "We're still in the very early stages of this investigation."

Capt. Marvin D. Renslow, 47, piloted Flight 3407. He began flying the Bombardier Dash 8 Q400 in December, having switched from another airplane. First Officer Rebecca Lynne Shaw, 24, had flown 774 hours in the Dash 8 Q400.

Noting that Renslow had 3,379 hours of total flight experience and the highest level of pilot certification available, Colgan Air defended its pilots' training and qualifications.

"Our crew training programs meet or exceed the regulatory requirements for all major airlines," the airline said in a statement. "Our ground and air training is designed in coordination with the aircraft manufacturer, one of the most respected providers of aviation flight training, and the Federal Aviation Administration utilizing state-of the-art training devices such as full-motion simulators, among others."

Independent aviation experts questioned whether any pilot would have been able to save the plane and its passengers, given that it was only 1,650 feet above the ground when it spun out of control.

"It depends on how deep the stall is, and whether you've got a good, clean ice-free aircraft, said Papadakis, who added that "this plane wasn't 'clean' " because the crew reported seeing an ice buildup on its wings.

That being the case, "the plane is probably unrecoverable at that point," said Kirk Koenig, president of Expert Aviation Consulting of Indianapolis and a commercial pilot for 25 years.

"A perfect airplane on a perfect day is probably recoverable" if it loses control at that altitude, Koenig said. "But not in the conditions they were in."

News Staff Reporter Lou Michel contributed to this report.