Sullenberger, who has blasted Boeing Co and the Federal Aviation Administration for their roles in the two 737 MAX crashes since October that killed 346 people, also said the U.S. system of certifying new aircraft is not working.

"Our current system of aircraft design and certification has failed us," he said.

His testimony came during a hearing meant to give lawmakers looking into Boeing and the 737 MAX crashes a better understanding of views on the steps needed to prevent similar crashes, particularly given the rising use of automation on airplanes.

Boeing said in May it had completed an update to software, known as MCAS, which would stop erroneous data from triggering an anti-stall system that automatically turned down the noses of the two planes that crashed, despite pilot efforts to stop it.

Sullenberger told the U.S. House Transportation and Infrastructure Committee that "it is clear that the original version of MCAS was fatally flawed and should never have been approved."

Allied Pilots Association President Daniel Carey told the committee that getting all pilots in simulators before the 737 MAX returns to service poses logistical issues, with 4,200 737 MAX pilots at American Airlines and 9,000 737 MAX pilots at Southwest Airlines.

Boeing has said that simulator training is not necessary, and is recommending a mandatory computer-based course that explains MCAS and could be completed at a pilot’s home in about an hour, according to pilot unions.

Acting FAA Administrator Dan Elwell said in May he had not decided on whether or not to require simulator training, but some foreign governments have also expressed support for additional simulator training.

Carey said pilots could get computer- and video-based training before the plane returns to service and then all could get into simulators within 10 months.

Committee Chairman Peter DeFazio criticized Boeing for failing to disclose details about the MCAS system to pilots. "The pilots didn't know it existed," DeFazio said.

DeFazio said Wednesday he plans a future hearing with Boeing. Boeing did not immediately comment on Wednesday.

Two people briefed on the matter said Boeing is set to conduct a certification flight as early as next week before it formally submits its software upgrade and training proposal.

Sharon Pinkerton, a vice president at Airlines for America, an industry trade group that represents American and Southwest, said airlines are relying on the FAA and the independent flight standard board for guidance.

"We are confident that working with those independent experts, involving our pilots unions, they will come to the right decision about what kind of training is needed and we will provide that training," Pinkerton told the panel.

Federal prosecutors aided by the FBI, the National Transportation Safety Board, the Transportation Department's inspector general, congressional panels and a number of independent committees are reviewing the 737 MAX's certification. Some in Congress have criticized the long-standing FAA practice of designating some certification tasks to Boeing or other aircraft manufacturers.

In a commentary in March on CBS MarketWatch, Sullenberger said "there is too cozy a relationship between the industry and the regulators" for proper oversight to be assured.

Major U.S. airlines have cancelled flights into early September because of the grounding of the 737 MAX.

Sullenberger managed to glide his Airbus A320 to a safe landing on the Hudson River after hitting a flock of geese shortly after takeoff, saving all 155 on board, in what became known as the "Miracle on the Hudson."

(Reporting by David Shepardson; Editing by Sonya Hepinstall and Tom Brown)

By David Shepardson