Boeing and Alaska Airlines have separately denied any legal responsibility for the injuries allegedly caused to dozens of passengers after a door plug blew out of a 737-Max 9 jet during a flight in January.

In its formal answers this week to a class-action lawsuit brought by dozens of passengers of Alaska Airlines Flight 1282, Boeing generally acknowledged the preliminary findings of a National Transportation Safety Board investigation that determined the door plug was improperly installed. The company also acknowledged that, in an interview with CNBC, Boeing CEO Dave Calhoun publicly described the incident as “our mistake.”

But Boeing denied liability for any damages alleged by the passengers, saying their lawsuit should be dismissed. The company also contended it cannot be held responsible for any injuries that may have resulted because its products were “improperly maintained, or misused by persons and/or entities other than Boeing.”

Likewise, Alaska Airlines denied liability, claiming that any injuries stemming from the door plug blowout “were caused by the fault of persons or entities over whom Alaska Airlines has no control … including Defendant The Boeing Company and/or non-party Spirit AeroSystems.”

Alaska Airlines also denied that the activation of the plane’s cabin-pressure warning light three times within the previous month — including on the day before the door incident —  was related or meant that the plane was unsafe to fly.    

The legal filings, submitted as part of the case in the U.S. District Court in Seattle, represent the first formal response from the companies to any of the several lawsuits filed in the wake of the Jan. 5 incident.

Daniel Laurence, an attorney representing passengers who are part of the class action, said Wednesday he was “frankly surprised” that Boeing and Alaska Airlines “don’t want to simply admit liability and put this case behind them.” 

“They’re putting up a wall and circling the wagons,” added Laurence, with the Strimatter Kessler Koehler Moore law firm in Seattle. “That’s disappointing, given what I think most of the population believes and the evidence appears to clearly support — that they put this aircraft into the air with an unsecured door plug that, had it come out a few minutes later, would have killed everybody on board.”

The incident occurred shortly after the Boeing-manufactured jet, carrying 171 passengers and six flight crew members, took off from Portland International Airport bound for Ontario International Airport in San Bernardino County, California. After reaching an altitude of about 16,000 feet, the door plug blew out, leaving a large hole in the plane’s fuselage and forcing the plane to turn back to Portland, where it landed safely.

Following the incident, which has brought new scrutiny to Boeing and its troubled 737 Max airplanes, the Federal Aviation Administration temporarily grounded some models of the plane. The NTSB investigation preliminarily found no bolts had been installed to secure the plug.

The FAA separately launched an audit into Boeing and its supplier, Spirit AeroSystems, finding “multiple instances where the companies allegedly failed to comply with manufacturing quality control requirements.” The Department of Justice has also separately opened a criminal probe into the door plug blowout, according to a source familiar with the investigation.

In the wake of the incident, at least three separate lawsuits have been filed by Flight 1282 passengers and their spouses, including cases in state courts in Washington and Oregon. 

Passengers involved in the federal lawsuit, seeking class-action status, claim they were physically injured and traumatized by the door plug’s blowout, which caused rapid depressurization of the plane’s cabin and led to widespread panic.

“The pressure change made ears bleed and combined with low oxygen, loud wind noise and traumatic stress made heads ache severely,” the lawsuit states. “Passengers were shocked, terrorized and confused, thrust into a waking nightmare, hoping they would live long enough to walk the earth again.”

Since the incident, some passengers have avoided flying on any airplane, and some have sought counseling to deal with emotional trauma, Laurence said.

The lawsuit also alleges that several passengers had trouble breathing in the aftermath of the door plug blowout because oxygen masks that dropped during the incident weren’t functioning.

Alaska Airlines denied that any oxygen masks did not work in its filing this week.

The airline acknowledged that the jet’s auto cabin pressure controller light had activated three times before the door plug blowout, leading Alaska Airlines to restrict the plane from flying on long routes over water. But the airline disputed that the light warnings “made the aircraft unsafe to fly (and) denies any correlation between the pressurization controller warning light activations and the door plug accident on Flight 1282,” its filing says.