Elaine Chao, U.S. secretary of transportation, delivers the keynote speech during the U.S. Chamber of Commerce Aviation Summit in Washington, D.C., March 7, 2019.

Boeing and the FAA , which certified the plane two years ago, are under increasing scrutiny after the crash of Ethiopian Airlines Flight 302 on March 10, which went down shortly after takeoff, killing all 157 people on board. Investigators who have extracted data from the airliner's black boxes said they detected " clear similarities " between the Ethiopian Airlines flight and a crash in Indonesia in October that killed all 189 on board.

The Department of Transportation on Tuesday asked the agency's watchdog to audit the Federal Aviation Administration's approval of Boeing 's 737 Max 8 aircraft after two fatal crashes of the new and fast-selling planes in less than five months killed 346 people.

"We will fully cooperate in the Department of Transportation's audit announced by Secretary Chao," Boeing said in a statement.

Hours after the DOT said it would seek an audit of the FAA's approval of the plane, President Donald Trump said he picked former Delta Air Lines executive Steve Dickson to lead the FAA. The agency has been without a permanent head since January 2018.

The U.S. last Wednesday joined dozens of other countries in ordering a grounding of the Boeing 737 Max planes.

The DOT certified Boeing's 737 Max 8, a re-engined and more fuel-efficient model of its workhorse jet that's been flying since the 1960s, in March 2017.

The Boeing 737 Max 8 features larger engines than previous models and to address potential in-flight stalls, Boeing added an automatic anti-stall system that points the nose of the plane downward, the way pilots recover from such a position. However, if the sensors that determine if the plane is in a stall receive erroneous data and point the nose down, the consequences could be catastrophic.

Investigators probing the doomed Lion Air crash in Indonesia have indicated that the pilots appeared to be battling the system and the similarities between that crash and the Ethiopian Airlines crash have increased scrutiny from lawmakers and regulators on Boeing and the FAA on the plane's launch.

Many pilots were not aware the system existed until after the Lion Air crash. For some of them, training consisted of an iPad presentation, less than an hour long, that explained the differences between the Boeing 737 Max plane and older models. The FAA did not mandate simulator training.

More than 370 of Boeing's 737 Max planes are in airlines' fleets worldwide and with more than 4,500 of them on order. Boeing shares rose 0.3 percent Tuesday to close at $373.43.

Read Chao's memo below: