Families of victims of the 2019 Ethiopian Airlines Boeing 737 MAX crash gathered Friday near the headquarters of aircraft manufacturer Boeing to denounce what they called "total impunity" over the loss of life.

"There has been no investigation, from a judicial point of view and from a criminal point of view, in the United States for manslaughter," said Catherine Berthet, who lost her daughter Camille in the accident.

Berthet, who is French, joined with other families from as far away as Canada and Germany as they brandished portraits of loved ones and stood in rain in protest outside the imposing headquarters of Boeing in suburban Virginia.

"Four years later... this plane is still in the air," she said.

On March 10, 2019, six minutes after takeoff from the Ethiopian capital of Addis Ababa and bound for Nairobi, Kenya, flight ET302 crashed in a field, killing all 157 passengers and crew.

The accident came barely five months after a similar tragedy in which a 737 MAX operated by Lion Air crashed into the Java Sea off Indonesia, killing 189 people.

The successive air disasters plunged Boeing into the worst crisis in its history, and forced the grounding of the worldwide MAX fleet for 20 months as investigators probed defects in its flight control software, the MCAS anti-stall system.

The aircraft was allowed to fly again in the United States in 2020.

"This plane is still dangerous," Berthet said. "Boeing must be sued for manslaughter... It's manslaughter and they have to be sued and DOJ has to do its work."

The US Department of Justice (DOJ) entered into a deferred prosecution agreement with Boeing that allowed its executives to skirt criminal charges. Instead, Boeing recognized that two employees misled authorities during the certification of the 737 MAX.

The airline manufacturer agreed to pay $2.5 billion in penalties and compensation in exchange for accepting the deal, which was negotiated out of the public eye.

Berthet and other families of victims are challenging the agreement in a federal court in Texas. A federal judge there ruled in early February that he did not have the authority to grant their petition, and the case is now under appeal.

Adnaan Stumo, brother of crash victim Samya Rose Stumo, said US prosecutors and Boeing lawyers "were on the same side of the courtroom against the family seeking justice... They struck a sneaky side deal."