The US Transportation and Justice departments 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 may be linked to inadequate pilot training on the plane's anti-stall system.

Dennis Tajer, spokesman for American Airlines' pilots union, told 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 last October, pilots have met with instructors and "requested if not demanded, simulators" for training, Tajer said.

American Airlines, which flies the 737 MAX, said, "Boeing 737-800 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 National Transportation Safety Board, which investigates plane crashes and other accidents, said pilots weren't trained in the use of the anti-stall device on flight simulators.

"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 handheld 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.

The Journal's report on the government's investigation cited "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, US Federal Aviation Administration and US 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, related documents and correspondence. The Justice Department's criminal division wants the documents turned over to investigators this month, the Journal reported.

A spokesman for Boeing declined to comment.

Separately, The Seattle Times reported on Sunday that federal regulators 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 prior practices at the FAA.

He wrote: "Rather than naming and supervising its own 'designated air worthiness representative', the agency decided to allow Boeing and other manufacturers who qualified under the revised procedures to elect their own employees to certify the safety of their aircraft."

In an interview on Monday, Hall told China Daily 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."

Hall wrote in the Times that involving airlines in certification of an aircraft hasn't worked well and first resulted in the grounding of Boeing's wide-body 787 Dreamliner.

In January 2013, a lithium ion battery sparked a fire on a Japanese Airlines 787 Dreamliner parked at Logan International Airport in Boston. There were no injuries. The NTSB blamed the first in part on "insufficient guidance for FAA engineers to use during the certification process to ensure compliance with applicable requirements."

Flight recorder data recovered from the planes shows "clear similarities" between this month's crash of an Ethiopian Airlines that killed 157 people and last October's crash of a Lion Air flight that killed 189, Ethiopian transportation officials said on Sunday.

While the causes of the crashes remain unknown, both planes flew erratically after experiencing difficulty shortly after takeoff with the Maneuvering Characteristics Augmentation System (MACS), the anti-stall system.

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 New York Times reported last week that pilots assembled a 13-page guide for the 737 MAX.

The 737 MAX, introduced in 2017, has flown in the US, Europe and China without a fatal crash. The US and 42 other nations, including China, grounded the plane following the fatal crashes in Indonesia and Ethiopia.

An "angle of attack" sensor built into the planes measures the amount of lift generated by the wings. The device warns pilots when there is too little lift, potentially stalling the plane, then points the nose of the plane down to gain speed.

Information contained on flight recorders for the Indonesian and Ethiopian planes has not been released, but analysts say the pilots may not have known how to turn off the anti-stall device after it pointed the nose of the plane down, and that may have been a factor in the crashes.