"The subject accident occurred because, among other things, Boeing defectively designed a new flight control system for the Boeing 737 MAX 8 that automatically and erroneously pushes the aircraft's nose down, and because Boeing failed to warn of the defect," according to the complaint.
Boeing is preparing to submit final paperwork to US regulators for a software upgrade for an anti-stall countermeasure on the 737 Max that investigators said in a preliminary report repeatedly pushed the nose down on the Max operated by Lion Air.
In that case, the jet went into a dive prior to crashing into the Java Sea in October.
Authorities are probing whether the system was a factor in the March 10 crash of the Ethiopian Airlines jet, which regulators said behaved similarly to the earlier downed plane.
Boeing faces the prospect of substantial payouts to the families of passengers if it's found responsible for both the Indonesia and Ethiopia crashes.
But legal experts say the second one could prove even more damaging for the company. That's because plaintiffs will argue the manufacturer was put on notice by the earlier tragedy that there was something dangerously wrong with its planes that should have been fixed.
Steven Marks, the lawyer who filed Thursday's complaint, criticised the certification process for the 737 Max 8, saying it amounted to an "amendment" of a 50-year-old model rather than a more rigorous approval process for a "new aircraft."
"Boeing and the FAA knew about the dangers and they failed to ground the fleet," said Marks, who also is suing over the Lion Air crash. He said the similarities between the two accidents are "very clear."
The single-aisle Max family is the Chicago-based planemaker's largest seller and accounts for almost one-third of the company's operating profit.
The crashes have put Boeing and the FAA under withering scrutiny, with multiple investigations being launched into the agency's certification of the 737 Max and its reliance on FAA-designated company employees to certify the safety of many of the planes' functions.
After the FAA grounded the 737 Max jets in the days following the Ethiopia crash, the manufacturer said it still has "full confidence" in the plane. Boeing Chief Executive Officer Dennis Muilenburg said the company was doing everything it could to understand the cause of the accidents, deploy safety enhancements and ensure that no more crashes happen.
The case is Debets v. Boeing Co., 1:19-cv-02170, US District Court, Northern District of Illinois (Chicago).
