Boeing's 737 Max aircraft is unlikely to re-enter service before August, according to the head of the airline industry's trade body, IATA.
Director General Alexandre de Juniac said "we do not expect something before 10 or 12 weeks", although he added a final decision was up to regulators.
The aircraft was grounded globally in March after two crashes within months.
It comes as Boeing boss Dennis Muilenburg issued another apology, saying "it feels personal".
The aircraft was grounded by regulators worldwide after 157 people were killed when an Ethiopian Airlines' 737 Max crashed. Five months previously a Lion Air 737 Max crashed, claiming 189 lives.
Mr de Juniac told reporters in Seoul on Wednesday that IATA was organising a summit with airlines, regulators and Boeing in five-to-seven weeks to discuss what is needed for the 737 Max to return to service, he said.
He hoped that regulators can "align their timeframe" on when the aircraft will be back in the skies.
US operators United Airlines, Southwest Airlines, and American Airlines have removed the 737 Max from their flight schedules until early to mid-August.
Later, Mr Muilenburg told US television station CBS that the crashes have had "the biggest impact on me" of anything in his 34 years at the planemaker.
In another apology, he said: "We are sorry for the loss of lives in both accidents, we are sorry for the impact to the families and the loved ones that are behind, and that will never change. That will always be with us. I can tell you it affects me directly as a leader of this company, it's very difficult."
Earlier in the day, Mr Muilenburg said he was confident about getting the 737 Max back in the skies.
He told an investor conference: "We're making clear and steady progress, and that includes the work that we're doing on the airplane update, the software update, working through the certification process with the FAA [US regulator]."
He said Boeing continues to expect to ramp-up its long-term production rate to 57 a month after cutting monthly output to 42 planes in response to the groundings.