ADDIS ABABA/PARIS/WASHINGTON--Europe and Canada said they would seek their own guarantees over the safety of Boeing's 737 MAX, further complicating plans to get the aircraft flying worldwide after they were grounded in the wake of two accidents killing more than 300 people.

  As the U.S. Federal Aviation Administration (FAA) analyses Boeing's plans for a software fix prompted by the first crash five months ago, the European Union's aviation safety agency EASA promised its own deep look at any design improvements.
  "We will not allow the aircraft to fly if we have not found acceptable answers to all our questions," EASA Executive Director Patrick Ky told an EU parliament committee hearing.
  Canada said it would independently certify the 737 MAX in the future, rather than accepting FAA validation, and would conduct an "exhaustive review" of the automated flight control system in MAX aircraft, known as MCAS, which experts believe may have played a role in both crashes. Canada also said it would send a team to help U.S. authorities evaluate proposed design changes and decide if others were needed.
  Boeing Co declined to comment. The company on Tuesday reshuffled the top executives in its commercial airplanes unit to focus on the accident investigations.
  U.S. government officials do not believe the two crashes will lead to a worldwide shift away from FAA certifications but U.S. lawmakers, as well as federal prosecutors, are scrutinizing the certification of the Boeing 737 MAX. The chairman of the U.S. House of Representatives transportation committee and another key Democrat asked the Transportation Department's inspector general on Tuesday to examine key decisions made by the FAA in certifying the 737 MAX jet for use.
  The FAA declined to comment on that request or on actions taken by other countries, but said in a statement that “the current, historic aviation safety record in the U.S. and globally is achieved through the FAA’s robust processes and full collaboration with the aviation community."
  The U.S. Transportation Department's inspector general plans to audit the FAA's certification of the jet, an official with the office said on Tuesday. The office can recommend changes or improvements to how the FAA operates. Boeing said it would cooperate with the audit.
  The unusual public intervention by two leading regulators came as a probe into the final minutes of Ethiopian Airlines Flight 302 turned toward secrets hidden in the cockpit voice recorder. The voices of Captain Yared Getachew and First Officer Ahmednur Mohammed could help explain the March 10 crash of the Boeing 737 MAX that has worrying parallels with another disaster involving the same model off Indonesia in October.
  The twin disasters killed 346 people, but there is no conclusive evidence so far that they are linked.
  Black box data was downloaded in France but only Ethiopian experts leading the probe have access to the dialogue between Getachew, 29, and Mohammed, 25. The data was back in Addis Ababa on Tuesday, sources familiar with the probe told Reuters.
  Experts believe the new MCAS system, which is designed to stop stalling by dipping the nose, may have been a factor in both crashes, with pilots unable to override it as their jets plunged downwards. Both came down just minutes after take-off after erratic flight patterns and loss of control reported by the pilots. However, every accident is a unique chain of human and technical factors, experts say.