The FAA is expected to face tough questioning in Congress Wednesday over its certification of the 737 MAX, which has been grounded after two deadly crashes

The US Federal Aviation Administration did not independently evaluate the safety of a Boeing 737 MAX system implicated in two deadly crashes, a person familiar with the matter said Tuesday.

The US regulator, as part of an internal review, has preliminarily concluded that FAA officials largely deferred to Boeing's assessments of the accident-ridden 737 MAX during the , the person said.

Boeing's top-selling 737 MAX narrow-body planes have been grounded globally since mid-March following two that killed 346 people. A common link in both crashes was the Maneuvering Characteristics Augmentation System.

During the FAA certification, Boeing did not flag to regulators that a failure of the MCAS could lead to a , a classification that would have triggered more regulatory scrutiny, The Wall Street Journal reported Tuesday.

The FAA approved the 737 MAX in early 2017 and the entered into service in May of that year.

In both the Lion Air crash in Indonesia in October and the Ethiopian Airlines crash in March, the MCAS pointed the plane sharply downward based on a faulty sensor reading, hindering pilot control after takeoff, according to preliminary investigations.

The FAA's internal review did not conclude that Boeing intentionally misled the agency, the source told AFP.

Rather, the agency concluded that further review was not needed of the MCAS because the FAA itself concluded the system did not affect the trajectory of the plane.

"The change to MCAS didn't trigger an additional safety assessment because it did not affect the most critical phase of flight, considered to be higher cruise speeds. At lower speeds, greater control movements are often necessary," an FAA spokesman said.

Boeing did not immediately respond to AFP requests for comments.

Acting FAA head Daniel Elwell is expected to face tough questioning on Boeing at a congressional hearing on Wednesday. At a prior hearing, lawmakers criticized the agency for being too cozy with Boeing and questioned why the agency was the last major regulator to ground the 737 MAX after other bodies took action.

Besides the FAA's internal review, the Boeing 737 MAX is the subject of numerous probes, including a criminal investigation by the Department of Justice.

American Airlines and Southwest Airlines, two US carriers that fly the 737 MAX, were subpoenaed by the US DOJ in November, said two people familiar with the matter.