The worldwide grounding of Boeing Co.’s 737 Max is taking its toll on airlines and it will be months before the plane returns to service, the head of the International Air Transport Association said.

Boeing’s fastest-selling aircraft, grounded by regulators after fatal crashes in Indonesia and Ethiopia, won’t resume flights until at least 10 to 12 weeks from now, Alexandre de Juniac, IATA’s chief executive officer, said on a call with reporters Wednesday.

“We are preparing a meeting between regulators, the aircraft manufacturer and the operators to make an assessment of the situation,” De Juniac said. “But it is not in our hands. It’s in the hands of regulators.”

IATA represents some 290 airlines, or more than 80% of total air traffic. The group will hold its annual meeting in Seoul this weekend, in the biggest gathering of airline and plane-company executives since the Boeing tragedies in October and March.

Bleak Assessment

De Juniac’s bleak assessment echoes the cautious stance adopted by aviation authorities on the timeline for the Max’s possible return.

European regulators, assessing proposed changes to the Max, plan to scrutinize the jet’s entire flight-control system before they approve a return to the skies, while U.S. aviation regulators said they won’t rush the matter. Indonesia, one of the biggest markets for the plane, signaled it may keep the jet parked until next year.

“The regulators aren’t on the same page,” De Juniac said in a phone interview. “Otherwise they’d have a similar timeline, a similar set of measures.”

Airlines, regulators and Boeing will meet in five to seven weeks to try and set a common timeline on when the Max could return to service and how trust could be restored, De Juniac said in the interview.

While the location has yet to be finalized, IATA would like to see a single regulator taking the call on airworthiness to avoid “useless complexity and additional costs,” he said.

Boeing, meanwhile, told SpiceJet Ltd. the 737 Max should be back in the air by July, signaling a quicker return for the plane than many expect. The Indian budget carrier is one of the biggest buyers of the jet.

“The timeline communicated to us based on their experience is July—end of June basically,” SpiceJet’s Chief Financial Officer Kiran Koteshwar said in an interview. “We are expecting it to be July.”

Representatives for Boeing in India didn’t comment.