The American aviation authority has no target date for when the Boeing 737 Max might be airborne again.
Speaking at an aviation conference in Texas, acting administrator of the Federal Aviation Administration (FAA), Dan Elwell, said there was no target date for getting the troubled jet re-certified to fly.
The Boeing 737 Max was grounded worldwide on 13 March, three days after the Ethiopian Airlines crash that killed 157 people shortly after take-off.
Initial estimates put the plane, implicated in two fatal crashes over the past seven months, as being in the skies again as early as April.
Boeing is currently working on a software upgrade to its MCAS anti-stall system.
Sources revealed to Reuters that the jet could be airborne as soon as late June, but Elwell told reporters the FAA’s only target was to endure the safety of the 737 Max.
It’s understood that the FAA has not yet carried out a test flight of the jet. Boeing said in April that it had completed 96 test flights using the new software.
“After the Lion Air crash, we didn’t have the information or data we needed to ground an aircraft,” Elwell told the BBC.
“The action that we took after the Lion Air accident was sufficient to make sure that, if that happened again, crews and operators could handle it.”
The grounding of the Boeing 737 Max, an upgrade to the narrow-body workhorse, has affected carriers around the world.
European operators including Tui, Norwegian and Ryanair have reported a drop in profits as they contend with the grounding, while in the US, operators American Airlines and Southwest have announced schedule changes until August to deal with the summer rush.
Earlier this week, three Chinese airlines said they had filed for compensation from the US planemaker.