Washington ? After three days of testimony about pilot fatigue, failed flying tests and cockpit warning systems, the uncle of a victim of crashed Flight 3407 summed up his frustration: “No one had to die. The behavior was beyond unprofessional.”

“This didn’t have to happen. That’s what came out of this,” said Terry Stelley, uncle of Coleman Mellett, 34, a passenger on the doomed flight. Stelley watched a webcast of the National Transportation Safety Board’s three-day hearing, from Cheektowaga, N.Y.

The board hasn’t reached a formal conclusion about what caused the worst U.S. air crash in more than seven years — its investigation isn’t complete — but the hearing that concluded Thursday exposed a slew of safety concerns involving the pilot training, hiring, pay and fatigue.

Continental Connection Flight 3407 ‘s captain, Marvin Renslow, and copilot, Rebecca Shaw, apparently didn’t realize they were traveling at dangerously low speeds as the Bombardier Dash 8-Q400, a twin-engine turboprop, neared Buffalo Niagara International Airport on the night of Feb. 12. The plane experienced an aerodynamic stall and plunged into a house below, killing all 49 people aboard and one on the ground.

Board member Debbie Hersman on Thursday raised the issue of a low air speed warning system in questioning NASA scientist Robert Dismukes, an expert on cockpit distractions. The plane lost more than 55 mph of airspeed in 20 seconds while Renslow and Shaw chit-chatted about careers and her lack of experience flying in icy conditions, she noted.

Dismukes agreed that the cockpit voice recorder shows the two were distracted, not realizing their danger until the stick shaker, a stall warning system that violently shakes the pilot’s control column, went off.

Asked by Hersman if pilots might benefit from an earlier, audible low-speed warning system, Dismukes said: “Absolutely, you want a very distinctive alert, but not one that is so dramatic. That’s well worth looking at.”

Hersman said the stick shaker warning came too late and was too sudden.

“I think this crew went from complacency to catastrophe in 20 seconds,” she said. “The room is on fire at that point.”

Testimony also indicated that Renslow and Shaw made critical errors that may have been the result of fatigue or insufficient training.

When the stick shaker went off, Renslow pulled back on the control column — the opposite of the correct action, which would have been to point the plane’s nose down to pick up enough speed to recover. Shaw, without waiting for an order from Renslow, retracted the aircraft’s flaps, which help keep the plane aloft at lower speeds.

Renslow, 47, and Shaw, 24, were based at Newark Liberty International Airport in New Jersey, but he commuted from his home near Tampa, Fla., and she lived with her parents near Seattle. Shaw flew cross-country overnight as a passenger to make Flight 3407. It’s not clear how much sleep either pilot had the previous night.

NTSB investigators said the pair may not have been able to afford to live in the New York metropolitan area on their salaries and might have been fatigued by their commutes and long work schedules.

Dismukes said studies show pilots are more vulnerable to distraction when they are fatigued.

Renslow also had failed several flight simulator tests before and after he was hired by Colgan Air Inc. of Manassas, Va., which operated the flight for Continental. He didn’t disclose his previous failures to Colgan when he was hired by the regional air carrier in 2005.

Sen. Byron Dorgan, the chairman of a Senate subcommittee aviation operations, safety and security, said he plans to hold a series of hearings beginning in June on safety issues arising from the hearings. Several New York House members also called for a congressional investigation.