Boeing Co. is aiming to conduct a key certification test flight on its grounded 737 MAX jet in late June, two people briefed on the matter said on Wednesday.

The 737 MAX has been grounded since March 2019 after two fatal crashes killed 346 people. Boeing told airlines it hopes to conduct the flight in late June, the sources said.

Asking for anonymity because they had not been authorized to speak publicly, they said Boeing had also notified airlines of a fix to address safety concerns about the placement of wiring bundles on the aircraft.

Reuters has previously reported that the Federal Aviation Administration (FAA) does not plan to clear Boeing for a resumption of 737 MAX flights until at least August.

The sources warned the date could slip into July for the certification test flight, as the dates for many milestones for returning the plane to service have been repeatedly pushed back.

The FAA said on Wednesday it was "in regular contact with Boeing as the company continues its work on the 737 MAX ... The aircraft will be cleared for return to passenger service only after the FAA is satisfied that all safety-related issues are addressed."

Boeing declined to comment.

In March, Reuters first reported Boeing would separate 737 MAX wiring bundles, flagged by regulators as potentially dangerous, before the jet returns to service.

In early April, Boeing confirmed it would make two new software updates to the 737 MAX’s flight control computer. But Boeing said software issues that prompted the updates were unrelated to a key anti-software system known as MCAS faulted in both fatal crashes.

Boeing (BA) resumed production of the 737 MAX on May 27 after halting it in January.

Bloomberg News reported the communication to airlines earlier Wednesday.

Boeing shares (BA) slid more than 5%.