The lawsuit, filed by the families of Sax, Carlson, Strickland and Rasmuson, accuses Boeing, Bell Textron, Rolls Royce Corps and Rolls Royce North America of negligence, negligent and fraudulent misrepresentation, and the failure to warn.

Tim Loranger, the lawyer representing the families in the lawsuit, told CNN on Thursday that ultimately the lawsuit alleges that the aircraft the Marines were on was known to have a defect but “insufficient steps have been taken to correct it.”

The lawsuit comes months after another deadly V-22 Osprey crash off the coast of Japan, which resulted in the deaths of eight US Special Operations airmen. The US military grounded its entire fleet of V-22 Ospreys in December as a result. That grounding guidance was lifted in March this year; officials said at the time an investigation identified a “materiel failure” responsible for the crash.

Col. Brian Taylor, the program manager of the Naval Air Systems Command V-22 joint program office, told reporters in March that the crash resulted from an “unprecedented” component failure, though he declined to say what component specifically failed or how.