The Federal Aviation Administration (FAA) and Boeing have completed certification test flights on the 737 Max, a key milestone towards the plane’s return to service, the US regulator said on Wednesday. The Max has been grounded since March 2019 after two crashes in five months killed 346 people. The FAA said it was yet to evaluate data from the three days of testing and had other tasks to complete. “The agency is following a deliberate process and will take the time it needs to thoroughly review Boeing’s work,” the FAA said. “We will lift the grounding order only after FAA safety experts are satisfied that the aircraft meets certification standards.” Boeing declined to comment. The tests of Boeing’s proposed changes to the automated flight control system on the aircraft are a pivotal moment in the company’s worst-ever corporate crisis. The FAA must complete the data review, approve new pilot training procedures, among other steps, and is unlikely to approve the plane’s return until mid-September. If that happens, the jet is on a path to resume US service before the end of the year, in a process hit by delays. The crisis has cost Boeing more than $18 billion (Dh66.1bn), slashed production and hobbled its supply chain, with criminal and congressional investigations still under way. In D ecember, Boeing fired chief executive Dennis Muilenburg after scrutiny into the jet’s design and the development tarnished its reputation with airlines and regulators. A Transportation Department inspector general report said Boeing did not disclose information to the FAA about an important safety system known as MCAS, which is linked to both fatal crashes. Boeing agreed to add significant safeguards to MCAS, make other software updates and move wiring bundles that the FAA said posed a safety hazard.