The Transportation Department's inspector general is also looking into the FAA's approval of the Boeing 737 Max, a United States official told AP.
Mourners in Addis Ababa, Ethiopia carry portraits of victims from the Ethiopian Airlines crash.
The system is created to bring the plan's nose down in the event the 737 is at risk of stalling - but can have catastrophic results if sensors receive erroneous information.
Muilenburg said the company was united with its airline customers, global regulators and government authorities in efforts to support the most recent investigation, understand the facts of what happened and help prevent future tragedies.
Boeing's boss has released a video message and open letter addressed to "airlines, passengers and the aviation community" in an attempt to provide reassurance after two crashes in five months involving its 737 Max planes.
Parallels between the two accidents have put the spotlight on whether Boeing delayed correcting a problem with the planes' MCAS anti-stalling system, identified after the Lion Air crash. In both cases, the 737 Max apparently failed to maintain a steady climb, veering erratically as if the pilots were struggling to keep control of the aircraft.
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The flip side is that Trump is likely talking about McCain's family not thanking him, but this is Trump we're talking about. Trump's feud with McCain dates back to well before he was elected president.
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Police are calling for anyone with footage of the incident not to share it on social media and to hand it to the police. Lauren was a bright and bubbly cheerleader and schoolgirl who lit up the lives of her friends, a close friend said.
Muilenburg said Boeing is examining the design and operation of the 737 Max and will make any appropriate changes.
In the Lion Air crash, sensors possibly misread the plane's performance and sent the jet into a dive to avoid a phantom stall. Boeing and the FAA have said that safety certification of the 737 Max met government requirements. One of the biggest unanswered questions: Was the plane's software to blame? A different flight crew experienced the same issue on a flight from Denpasar to Jakarta the previous day, but had turned off the MCAS and took manual control of the plane, the report said.
Boeing shares fell 1.8 per cent to $372 at end of trading in NY on Monday.
The report quoted unnamed Boeing and FAA experts who claimed that the company subsequently delivered an analysis that contained crucial flaws and out of date information. A Boeing representative declined to comment.
Citing people familiar with the inquiry, the Wall Street Journal reported on Sunday that U.S. Department of Transportation officials were scrutinizing the FAA approval of MAX jets and that a grand jury in Washington subpoenaed at least one person involved in developing the MAX.
Norwegian Airlines has already said it will seek compensation after grounding its MAX aircraft, and various companies are reconsidering orders.