(CNN) Debate over the factors that may have contributed to two 737 Max plane crashes consumed a House hearing Wednesday, as two pilots criticized Boeing's design and rollout of the aircraft and some lawmakers questioned the qualifications of the foreign pilots involved in the crashes.

While investigations into the 737 Max and crashes involving the aircraft in Ethiopia and Indonesia remain ongoing, the Federal Aviation Administration has identified similarities between the crashes, in which 346 people died. The plane's automatic safety feature known as MCAS , which pushes the nose of the aircraft down if it senses an imminent stall, is believed to have played a role.

Chesley "Sully" Sullenberger, the hero pilot credited with the 2009 " Miracle on the Hudson ," said Wednesday that the design of the Boeing 737 Max allowed for single device failures on the aircraft to have "cascading effects" that could confuse and overwhelm pilots.

"We should design aircraft for them to fly that do not have inadvertent traps set for them," said Sullenberger, referring to MCAS and what he described as Boeing's previous failure to alert pilots to that system's existence and function on the aircraft.

He said aviation manufacturers needed to develop better safety-analysis processes to holistically examine aircraft designs for risks.

Daniel Carey, the president of the Allied Pilots Association, which represents American Airlines pilots, also said Wednesday that Boeing had mistakenly created MCAS as a single-point-of-failure system, meaning that if one part of it failed, pilots would have to identify and correct that error.

He said Boeing had failed to disclose the existence of MCAS to pilots and to provide adequate 737 Max training materials for pilots trained on older 737 models.

While both Carey and Sullenberger recommended additional training requirements for 737 Max pilots, Sullenberger said simulator training should be mandatory before the aircraft returns to the skies.

"Reading about it on an iPad is not even close to sufficient," Sullenberger said.

Carey said pilots could get computer- and video-based training, then receive simulator training in the months after the aircraft returns to service, though he expressed concern about the updated training materials and protocols Boeing has suggested.

Carey said that at a meeting between pilots and the FAA in April, the FAA highlighted a checklist Boeing had directed pilots to use in the event of an MCAS misfire that an agency official said had not been validated since 1967.

Previously, pilots transitioning to the Boeing 737 Max from prior 737 models were given a short, self-administered online course that did not mention the MCAS system.

Boeing's proposal to bring back the 737 Max has included a computer-based training program that, like the requirements before the two crashes, does not involve hands-on simulator training. The FAA has not announced any decisions on final training requirements, however.

Some Aviation Subcommittee members during Wednesday's hearing questioned the qualifications of foreign pilots and the standards of the International Civil Aviation Organization, the United Nations' aviation agency.

"The pilots of Ethiopia Air, their hours give me a great deal of question," said Rep. Paul Mitchell, a Michigan Republican, referring to the experience of the pilots involved in the Ethiopia crash. "We need to look at the ICAO standards versus our standards in North America for pilot qualifications and training and reconcile that."

Rep. Sam Graves, a Missouri Republican, cautioned against jumping to predetermined conclusions about the factors that contributed to the crashes, though he listed his main concerns.

"In reading the preliminary accident reports I, as well as, obviously, many others with a lot of flying experience, many have also raised concerns with the pilot training, with pilot experience, with aircraft maintenance and definitely with airline operations. All of these issues have to be investigated," Graves said.

Boeing CEO Dennis Muilenburg and others have argued that the actions of the pilots played a role in the chain of events that led to the crashes in Ethiopia and Indonesia in March and last October.

Muilenburg has said his company made a mistake in its disclosures related to a 737 Max safety light that was not operating on all aircraft, though he said in April that the aircraft's systems were properly designed and the pilots did not "completely" follow procedures Boeing had outlined.

Carey, the union president, said he was "offended" by insinuations that pilots were to blame for the crashes and described Ethiopian Airlines pilots as "world-class."

"To make the claim that these accidents would not happen to US-trained pilots is presumptuous and not supported by fact," Carey said in prepared remarks. "Vilifying non-US pilots is disrespectful and not solution-based, nor is it in line with a sorely needed global safety culture that delivers one standard of safety and training."

The Boeing 737 Max has been grounded worldwide since March. While Boeing said in May that it had finalized the development of a fix for the plane's MCAS system, no time frame for the aircraft's return to the skies has been announced.

A source with knowledge of the process says the FAA certification flight of the Boeing 737 Max is expected to take place in the next two weeks. The certification flight is the next step to getting the planes back in the air, but not the final step.

The source says it will take four to six weeks to validate the findings of the flight once it's complete. If the changes to the 737 Max are approved, US airlines are expected to fly the aircraft again after September, the source said.