Federal aviation officials offered no further details on a time line for the return to service of the Boeing (BA - Get Report) 737 Max aircraft during a meeting with regulators from around the globe Monday.

The gathering involved more than 50 regulators who will participate in approving the return to flight of the troubled aircraft in their respective countries.

"The FAA continues to follow a thorough process, not a prescribed time line, for returning the aircraft to passenger service. The FAA has a transparent and collaborative relationship with other civil aviation authorities as we continue our review of changes to software on the Boeing 737 MAX," the agency said in a statement about the meeting.

FAA Administrator Steve Dickson told the regulators the agency "would continue to share information about the FAA's activities to ensure the proposed changes to the automated flight control system on the 737 MAX meet certification standards," according to the statement.

Shares of Boeing fell $2.36, or 0.6%, to $377.03 Monday. The 737 Max model was grounded in March following the second of two fatal crashes involving the plane.

Subsequent probes have focused on the plane's flight control system as the likely cause of the crashes which occurred in otherwise good flying conditions. 

Airlines have repeatedly pushed back their expectations of when the planes will return to service, with some canceling flights involving the aircraft until December.