Relatives of Boeing Co 737 MAX crash victims on Tuesday urged the European Union Aviation Safety Agency (EASA) to delay approving the aircraft's return to service, saying there are unanswered questions about its safety.

A Boeing 737 Max airplane sits parked at the company's production facility in Renton, Washington, the US on Wednesday. Photo: AFP

In November, the US Federal Aviation Administration cleared the jet following design changes around systems involved in two crashes that together killed 346 people in 2018 and 2019, sparking a global grounding and safety reviews. EASA has said it could formally lift its own ban in January 2021, once public and industry feedback on its conditions for putting the jet back into service have been studied.

In a letter to EASA Executive Director Patrick Ky and in comments filed with the agency, relatives and friends of Ethiopian Airlines crash victims said it should first finish its analysis of the modified aircraft and complete its safety report on the crash.

"It would be impossible for EASA to conclude that the revised 737 MAX is safe before its own safety assessment is complete," they said in the letter.

An EASA spokesman said the agency does not comment on any received feedback at this stage of the recertification process. It plans to publish the final airworthiness directive in January 2021, once feedback has been reviewed, he said.