The US departments of transportation and justice are reportedly reviewing how Boeing Co's 737 Max aircraft was certified for commercial flight prior to fatal crashes in Indonesia and Ethiopia, both of which might be linked to inadequate pilot training on the plane's anti-stall system.

Dennis Tajer, spokesman for American Airlines' pilots union, told the news website Quartz that training for the use of the anti-stall system was limited to "an iPad lesson for an hour".

Since the Lion Air crash of a Max 8 in Indonesia in October, pilots have met with instructors and "requested, if not demanded, simulators" for training, Tajer said.

American Airlines, which flies the 737 Max, said, "pilots were required to receive some additional training on the Max 8, which included an hour lesson on some differences. Additional training wasn't required, as the 737-800 and the Max 8 have 'same type' certification."

James Hall, former chairman of the US National Transportation Safety Board, which investigates plane crashes and other accidents, said pilots weren't trained on flight simulators in the use of the anti-stall device.

"The simulator is the fundamental tool for training pilots," Hall, now an aviation consultant in Washington, told China Daily.

"At present, there is not an approved simulator for this equipment," he said. "So we ended up with pilots getting training on a hand-held device. I think that will be one of the things carefully looked at and it may delay the return of this plane to service."

The transportation and justice departments' investigations, apparently proceeding on civil and criminal tracks, could raise questions about the growing use of Boeing's employees to certify the safety of its own aircraft with limited oversight from federal regulators, The Wall Street Journal reported on Monday, citing "people familiar with the matter".

The newspaper said the subpoena seeking documents listed a prosecutor from the Justice Department's Criminal Division as a contact. The US Department of Transportation, Federal Aviation Administration and Department of Justice didn't return calls from China Daily seeking comment.

A grand jury in Washington issued a subpoena on March 11 seeking information on the development of the jetliner, as well as related documents and correspondence. The Justice Department's Criminal Division wants the documents turned over to investigators this month, the Wall Street Journal reported.

A spokesman for Boeing declined to comment.

Separately, the Seattle Times reported on Sunday that federal regulators had delegated much of the plane's safety review to Boeing and that the company's analysis contained key flaws.

In an opinion piece published last week in The New York Times, Hall questioned the US aircraft industry's use of its own employees to certify the safety of an airplane, a departure from previous practices at the FAA.

Hall told China Daily on Monday that the same lack of government oversight may have led to problems with Boeing's 737 Max.

"The certification process is at the heart of the aviation industry's safety culture," Hall said. "The US government is built on checks and balances, and if we don't have checks and balances in the aviation industry, we have problems.

"I think the process may have outstripped the ability of Congress to maintain a strong regulatory system," he said. "We put a man on the moon and we're looking at self-driving vehicles - we can (solve this problem) and we need federal oversight."

Flight recorder data recovered from the planes show "clear similarities" between the crash on March 10 of an Ethiopian Airlines Boeing 737 Max 8 that killed 157 people and the crash in October of a Lion Air flight, also a Boeing 737 Max 8, that killed 189, Ethiopian transportation officials said on Sunday.

While the causes of the crashes have not yet been determined, both planes flew erratically after experiencing difficulty with the planes' anti-stall system shortly after takeoff.

Pilots said they first learned of potential difficulties with the new anti-stall system after the Lion Air crash. The FAA then ordered 737 Max manuals to be updated, and Boeing issued information telling pilots how to override the system.

The US and 42 other nations, including China, have grounded the plane following the two crashes.