Aviation experts say federal investigators seem to be focusing on possible pilot error to explain why Continental Connection Flight 3407 plunged to the ground in Clarence Center on Feb. 12 and took 50 lives.

The experts say that while every aviation crash is a series of events, the one factor they cannot explain is why the pilot of the Bombardier Dash 8 Q400 pulled back on the yoke, causing the twin-engine turboprop plane to suddenly jerk upward before spinning out of control after the plane’s stall alarm activated.

“They’re still investigating,” Kirk Koenig of Expert Aviation Consulting told The Buffalo News, “but it sounds like to me they’re starting to try to say this is a pilot issue.”

Koenig, as did other experts consulted by The News, said the proper response to a stall is to lower the plane’s nose to recover airspeed, increase the power and level the wings.

Instead, data that the National Transportation Safety Board released Wednesday said that when the stall alarm activated, there was a 25-pound pull on the yoke.

“That is just so precisely wrong,” said M. P. “Pappy” Papadakis, an aviation lawyer and pilot. “Unless there is some new magic I didn’t learn, it dates back to your first or second flight in the airplane.”

Stephen Frederick, a pilot and author of a book on an earlier turboprop crash in Indiana, said: “It almost seems like it’s an improper response,” referring to raising the plane’s nose to counteract the stall. “But I hate to jump on the back of dead pilots at this point with that limited information.”

As all three of these experts pointed out, the safety board still has not come up with a definite cause of the accident, and the investigation continues.

A spokesman for the airplane’s manufacturer, Bombardier, said that it would have no comment until the safety board investigation is complete.

Colgan Air, operator of the flight, also said the investigation is not complete and declined to comment on any possible cause.

“It’s important not to jump to conclusions, and instead focus on what is factual and released by the investigating team at the NTSB,” said a statement released by the company. “Nothing in [Wednesday’s] announcement pinpoints a cause, nor does it offer theories on a cause, as was suggested in some news reports. Again, the only absolute fact is that we do not know the cause of this accident.”

Colgan again stressed that its pilots are well-trained and ready to handle any emergency.

The safety board will conduct a public hearing on the accident in Washington from May 12 to 14, said Mark V. Rosenker, acting chairman of the board.

“The tragedy of Flight 3407 is the deadliest transportation accident in the United States in more than seven years,” said Rosenker, who will preside over the hearing. “The circumstances of the crash have raised several issues that go well beyond the widely discussed matter of airframe icing, and we will explore these issues in our investigative fact-finding hearing.”

While the safety board has not ruled out icing as a cause, it pointed out that its modeling and simulation showed that “icing had a minimal effect on the airplane.”

Preliminary examination of the airplane systems, according to the safety board, revealed that there were no indications of system failures or anomalies before the crash.

The Federal Aviation Administration’s Civil Aerospace Medical Institute toxicology lab tested the flight’s pilot and copilot and ruled out any effect from drugs or alcohol.

Co-pilot Rebecca Lynne Shaw, 24, tested negative for drugs and alcohol, and pilot Marvin D. Renslow, 47, tested negative for everything but diltiazem, a prescription blood pressure medication that the FAA had approved for use by air crews.

Among the issues the safety board is studying are “sterile cockpit rules” — which bar pilots from non-essential conversation and activities — crew experience, fatigue management and stall-recovery training, the safety board said.

All members of the safety board will participate in the hearing, but the agency has not yet detailed which other parties will participate.

The detailed update of the investigation appears to downplay the role of icing on the plane’s wings or tail as a possible cause of the accident.

The crew encountered “variable periods of snow” and “light to moderate icing” on its approach to Buffalo Niagara International Airport, the safety board update said.

The flight data recorder and airplane performance models indicate that “some ice accumulation was likely present on the airplane prior to the initial upset event but that the airplane continued to respond as expected to flight control inputs throughout the accident flight,” the report said.

The plane’s systems appeared to be operating properly, but more tests will be done on the de-icing mechanism.

“It sounds like to me they’re trying to grease it up to say this is going to be pilot error,” said Koenig of Expert Aviation Consulting. “It’s much more complicated than saying a pilot did this or this piece broke or why. And that’s why they’re bringing in all these other things, like fatigue management.”

Frederick, as did the others, said that it is still too early to discount the effect that icing on the wings had on the Bombardier aircraft.

But he, too, wonders why the pilot took the plane up to try to counter the stall.

“One of the things they are also looking at, frankly, is an inappropriate pilot response,” Frederick said. “That’s always a possibility in a confusing situation. You always run the risk of the pilots exacerbating the problem rather than solving it when things are happening very fast.”

An FAA warning to pilots in January indicated a glitch in the instrument landing system’s “glide slope guidance signal” leading to the runway. The anomaly involves one of the series of ground-to-plane signals along the runway approach, which falsely indicate that aircraft are flying above their actual altitude.

“To date,” the safety board said, “investigation into these reports has not revealed any connection to the accident flight.”

mbeebe@buffnews.com and jzremski@buffnews.com