NEW YORK, United States (AFP) — Boeing said Monday that the flight stabilisation system under scrutiny following two deadly 737 MAX plane crashes, met all US regulations.

“The 737 MAX was certified in accordance with the identical Federal Aviation Administration requirements and processes that have governed certification of all previous new airplanes and derivatives,” Boeing said Monday.

Boeing and regulators face increased examination over the stall prevention system, the Maneuvering Characteristics Augmentation System or MCAS, which authorities have said was likely a factor in deadly crashes in Indonesia in October, while the crash in Ethiopia earlier this month showed similarities.

“The FAA considered the final configuration and operating parameters of MCAS during MAX certification, and concluded that it met all certification and regulatory requirements,” Boeing added.

Since the Ethiopian crash, which claimed 157 lives, questions have been raised not only about Boeing, but also the FAA and its close relationship with the company.

While it may take months for definitive conclusions, experts are asking why the MCAS was given the green light despite objections by American pilots who had voiced concerns with the system.

Investigation into the Lion Air crash in October implicated the MCAS which can erroneously force the plane down when the autopilot is engaged, if it detects the plane may be at risk of a stall. Both crashes happened shortly after takeoff.

American pilots had complained of the flaw, and Boeing has been working on a software upgrade to the system and issued new instructions about how to override the issue in the meantime.

In service since May 2017, the 737 MAX 8, one of several variants of the 737 MAX, has now experienced two deadly tragedies, a scenario that is unprecedented for a new aircraft.

The US Transportation Department’s inspector general is probing the FAA’s approval of the MCAS, the Wall Street Journal reported.

The newspaper also said the criminal division of the Justice Department was looking into the development of the plane.

The 737 MAX was certified as a variant of the 737 Next Generation, the plane it replaced, despite major differences in the engine and the MCAS, according to documents available on the FAA’s website.

But because of budget constraints, the FAA delegated aspects of the approval process to Boeing itself, according to sources.

Under a program, known as the Organization Designation Authorization (ODA), employees of Boeing are accredited by the FAA to assist in approving the aircraft — including design, production, flight tests, maintenance and other systems — as well as signing off on the training procedures of pilots on new planes.