WASHINGTON (Reuters) – The Federal Aviation Administration and Boeing Co have completed certification test flights on the 737 MAX, a key milestone toward the plane’s return to service, the U.S. regulator said on Wednesday.

The MAX has been grounded since March 2019 after two fatal crashes in five months killed 346 people.

The FAA said it must still evaluate data from the three days of testing and has 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, saying it would defer to the FAA statement.

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 ungrounding until mid-September, Reuters reported this week.

If that happens, the jet is on a path to resume U.S. service before year-end, in a process plagued by delays.

The crisis has cost Boeing more than $18 billion, slashed production and hobbled its supply chain, with criminal and congressional investigations still ongoing. In December, Boeing fired Chief Executive Dennis Muilenburg after scrutiny into the jet’s design and development tarnished its reputation with airlines and regulators.

A Transportation Department inspector general report first reported by Reuters on Tuesday faulted Boeing for not disclosing information to the FAA about a key safety system known as MCAS tied 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.

Reuters
Photo Rob Vogelaar