US aviation regulators have defended their response to two fatal Boeing 737 Max plane crashes.
The Federal Aviation Administration (FAA) told the BBC that it didn't have the information needed to ground the 737 Max after the Lion Air crash.
Civil aviation authorities from 33 countries gathered in Texas on Thursday to discuss when the current grounding order should be lifted.
The FAA said it was making sure that the 737 Max was "as safe as possible".
An Ethiopian Airlines flight crashed in March, killing all 157 people on board.
It followed the Lion Air disaster in Indonesia in October, in which 189 people died.
Boeing grounded its entire global fleet of 737 Max aircraft in March after the two crashes.
"After the Lion Air crash, we didn't have the information or data we needed to ground an aircraft," Dan Elwell, the FAA's acting administrator told the BBC.
"The action that we took after the Lion Air accident was sufficient to make sure that the world... if that happened again, could handle it, that the crews and operators could handle it."
Mr Elwell said that he could not comment on the active investigations into the two crashes, and that the FAA, together with international aviation authorities, was examining links found between the interim reports into each plane crash.
"I'm confident that, working together, we're going to fix it, and the 737 will go on to be as the 737 varieties before it - the safest planes in the sky."
The FAA has not set out a timetable for when the 737 Max will return to service.
Mr Elwell said if it took a year for the grounding order to be lifted "so be it".
The regulator said that during the meeting, it would provide its "safety analysis that will form the basis for our return to service decision process".
The FAA also said it "will provide safety experts to answer any questions participants have related to their respective decisions to return the fleet to service".
At the same time as the FAA is meeting regulators in Texas, the International Air Transport Association (IATA) is holding a separate meeting in Montreal, Canada, with 737 Max airline operators from across the world.
Earlier, officials for American Airlines, United Airlines and Southwest Airlines told Reuters that once the order is lifted, it would take between 100-150 hours of preparation before the grounded 737 Max planes will be ready for flying.
The Mcas system
Boeing has developed a software update for the Manoeuvring Characteristics Augmentation System (Mcas) on the 737 Max - a new feature on the jet designed to improve the handling of the plane and to stop it pitching up at too high an angle.
Mcas has been linked to both the Ethiopian Airlines crash in March, which killed 157 passengers and crew, and the Lion Air disaster in Indonesia at the end of October, in which 189 people perished.
However, Boeing has not formally submitted the software fix to the FAA.
Mr Elwell said: "We're going to make sure that when the 737 Max flies again, that the Mcas system and the inputs that make the Mcas system activate are refined in a way that makes the aircraft as safe as possible."