The US Federal Aviation Administration (FAA) says it is too early to commit to a date for when the Boeing 737 Max will return to service, as the regulator completes a day-long meeting with dozens of global aviation regulators to discuss the troubled aircraft.
"I'm not going down the timetable route. The only timetable we have is the analysis that says the Max is good to fly and safe to fly," acting FAA administrator Dan Elwell told reporters following an eight-hour-long meeting in Fort Worth with aviation regulators from more than 30 countries.
"It is the one thing that we can't be nailed down to. Because the last thing I want is to put a date out there and have anybody, either the FAA or you or the public, drive to the date instead of the end result or the process," says Elwell.
Airlines around the world have varying projections on when their 737 Max aircraft will resume flights. US carriers have removed the type from their schedules through July or August, while other airlines expect the grounding to be lifted earlier.
Characterising today's meeting with other aviation regulators as "collegial" and "exceedingly positive", Elwell says the FAA's counterparts used the gathering as an opportunity to ask questions, rather than make recommendations.
While he says that a "global decision" to unground the 737 Max will instil public confidence in the aircraft, he also acknowledges that each country's aviation regulator has the final say on when to lift the grounding on the 737 Max in their respective jurisdictions.
The FAA came under an onslaught of criticism for being the last major aviation regulator to ground the 737 Max on 13 March – three days after the second fatal crash of a 737 Max 8 in less than five months. Before grounding the aircraft, the agency had insisted for days that it saw no basis to take action, raising concerns in a global industry previously used to trusting the regulator's leadership in aviation safety.
Elwell, sounding frustrated at reporters' questions, defended the delay. He says that the regulator was not presented satellite data that convinced it to ground the aircraft, until the morning of 13 March. That satellite data, which showed possible similarities between the flying profiles of the two deadly crashes, prompted Canada to ground the 737 Max on the same day.
Defending the FAA as a "data-driven organisation", Elwell says the FAA had previously analysed data from 57,000 flights operated by the 737 Max in the USA, searching for any abnormalities related to trim tabs and angle-of-attack vanes.
"Did we have any evidence of a problem? And the answer was no, zero. Does that suggest that because we found zero, that I'm sure every US pilot would have handled that situation objectively? No. But what we had to go by is data. If we had seen evidence of a trend in that regard, our metric and decision making would have been different," he says.
The regulator is awaiting Boeing's completed application for the software upgrade to the 737 Max's Manoeuvring Characteristics Augmentation System (MCAS), which was implicated as a factor in both crashes.
Once received, the FAA will undertake an analysis of Boeing's submission while taking into account recommendations of a technical advisory board, which comprises experts from various US agencies. The FAA will participate in 737 Max test flights with the software upgrade as well, says Elwell.
Boeing announced last week that it had completed the software upgrade for MCAS, and was working to provide "additional information" to address FAA requests including "additional detail on how pilots interact with the airplane controls and displays in different flight scenarios".
A Boeing spokesman was not immediately able to provide a timeline for when the manufacturer will submit the final MCAS package to the FAA. The manufacturer says in a statement: "Once we have addressed the information requests from the FAA, we will be ready to schedule a certification test flight and submit final certification documentation."
Elwell declines to say for certain if the MCAS upgrade will necessitate simulator training, but notes that proposed changes to MCAS are "less intrusive and burdensome" than the original MCAS, which did not require simulator training.
Some 737 Max operators have indicated that they don't expect simulator training, and thus minimise crew training time for the aircraft to resume service. FAA officials estimate that it would take operators "two to three days" to "maybe a week" to return their parked aircraft to service, after the fleet is cleared to fly again.
More than 370 aircraft were suspended from flying by over 50 operators in the days following a global grounding of the 737 Max in March, shows Cirium's Fleets Analyzer.