Boeing is under increasing pressure after investigators found similarities between the crashes of two Boeing 737 MAX planes in Ethiopia and off Indonesia.
Investigators probing the Boeing 737 MAX crash in Ethiopia have found similarities in vital flight angle data with an aeroplane that came down off Indonesia, a source says.
The Ethiopian Airlines disaster eight days ago killed 157 people, led to the grounding of Boeing's marquee MAX fleet globally and sparked a high-stakes inquiry for the aviation industry.
Analysis of the cockpit recorder showed its so-called "angle of attack" data was "very, very similar" to the Lion Air jet that came down off Jakarta in October, killing 189 people, a person familiar with the investigation said.
The angle of attack is a fundamental parameter of flight, measuring the degrees between the air flow and the wing. If it is too high, it can throw the plane into an aerodynamic stall.
A flight deck computer's response to an apparently faulty angle of attack sensor is at the heart of the ongoing probe into the Lion Air crash.
Ethiopia's Transport Ministry, France's BEA air accident authority and the US Federal Aviation Administration have all said data shows similarities between the two disasters.
Both planes were 737 MAX 8s and crashed minutes after takeoff, with pilots reporting flight control problems.
Under scrutiny is a new automated system in the 737 MAX model that guides the nose lower to avoid stalling.
Lawmakers and safety experts are asking how thoroughly regulators vetted the system and how well pilots around the world were trained for it when their airlines bought new planes.
Boeing has halted deliveries of its best-selling model that was intended to be the industry standard but is now under a shadow.
There were more than 300 MAX airplanes in operation at the time of the Ethiopian crash, and nearly 5000 more on order.
After a 10 per cent drop last week that wiped nearly $US25 billion ($A35 billion) off its market share, Boeing stock slid about 2.3 per cent on Monday to $US370 ($A522).
Weekend media reports heaped further pressure on Boeing.
The Seattle Times said the company's safety analysis of the MCAS system had crucial flaws, including understating power.
It also said the US FAA followed a standard certification process on the MAX rather than extra inquiries. The FAA declined to comment, but has said the process followed normal process.
The Wall Street Journal reported that prosecutors and US Department of Transportation were scrutinising the FAA's approval of the MAX series, while a jury had issued a subpoena to at least one person involved in its development.
Boeing and the FAA declined to comment on that.