CHICAGO (Reuters) - 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. Last month, the U.S. 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 next month, 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, once all the feedback has been reviewed, he said. The families also called into question the U.S. Federal Aviation Administration’s decision to lift its flight ban following a Senate Commerce Committee report on Friday that concluded the agency and Boeing officials colluded during 737 MAX recertification testing. They urged EASA to explain why Boeing’s changes make the aircraft safe and to require that it increase the plane’s safety margins by implementing a third Angle of Attack sensor. They also called for redesigning the flight deck and crew alert system “to meet modern safety standards,” among other steps.