Boeing Co and lawyers representing families of victims of a 737 MAX crash agreed in court on Wednesday to hold a conference call with U.S. government crash probe authorities over access to documents related to the now-grounded aircraft's design, development and two fatal disasters involving it.

Boeing has resisted sharing documents sought by lawyers representing families of victims of an Ethiopian Airlines 737 MAX crash on March 10, which killed 157 people five months after a similar Lion Air disaster in which 189 people died.

The lawyers, who are asking why the MAX continued flying after the first crash, say the materials are critical for assessing liability by Boeing and punitive damages.

"They're hot documents," Robert Clifford, lead counsel for the plaintiffs, told reporters, saying some show what and when Boeing knew about factors that played a role in the Lion Air accident.

Boeing has argued that the U.S. National Transportation Safety Board (NTSB) is restricting release of the documents under international guidelines on crash probes and that they are confidential.

The plane, once Boeing's fastest-selling jet, has been grounded globally since mid-March while Boeing addresses software and training issues involved in both disasters, costing the planemaker nearly US$19 billion.

The NTSB seemed to switch its stance on some of the documents in a Feb. 18 letter to Boeing, one topic of Wednesday's hearing in U.S. federal court in Chicago before U.S. Magistrate Judge David Weisman.

Boeing and the plaintiffs' lawyers agreed to brief the court on the outcome of a conference call with NTSB assistant general counsel Benjamin Allen scheduled for Thursday.

Chicago-based Boeing is in the process of settling a separate batch of lawsuits related to the Lion Air crash, but families of the Ethiopian crash are seeking a jury trial.

Following 737 MAX testimony from Boeing executives at congressional hearings in Washington, Ethiopian crash victim lawyers want to know whether the planemaker hid materials.

Dan Webb, a lawyer for Boeing, rejected in court the notion that documents have been hidden, saying that some "haven't been produced yet."

"Boeing takes very seriously its legal obligations and is working with the plaintiffs in good faith, and consistent with our obligations as a technical advisor to the NTSB, to provide the information they need to pursue their claims," the company said in an emailed statement, adding that it was cooperating fully with investigative authorities.

A Lion Air investigation faulted Boeing's design of the 737 MAX but said the airline also made mistakes.

The Ethiopian probe is still ongoing, nearly a year after the crash.