Fort Worth (USA) (AFP)

The world's civil aviation authorities, meeting Thursday in Texas, were examining the case of the 737 MAX immobilized for more than two months, with a nagging question: when Boeing's flagship plane will be able to revolve?

The day before, Dan Elwell, the acting head of the US Federal Aviation Agency, the FAA, choked a chill by revealing that Boeing had not submitted for evaluation the update of the MCAS anti-stall system, in because of additional questions.

It is the malfunction of this device, implicated in the accident of a 737 MAX 8 Ethiopian Airlines on March 10 (157 dead) and a similar copy of Lion Air October 29 in Indonesia (189 deaths), which led to the temporary ban on theft of this aircraft, the latest from the American manufacturer.

The aircraft manufacturer had said last week that the patch was ready for certification.

"It takes a lot more time than expected, maybe they want to make sure they do things right," said Richard Aboulafia, an expert at Teal Group. "There are many things at stake, including the first impression of global regulators" by reviewing the fix.

- "Several months" -

For Michel Merluzeau, "we are moving towards a return to service that may spread over time". According to this expert at Air Insight Research, one can imagine a lifting of the ban in the United States by the end of the summer and in "several months" in other countries.

The US airlines operating the 737 MAX - American Airlines, Southwest and United Airlines - were hoping to put the plane back into their flight programs by mid-August at the latest.

Boeing's latest delay is due to the fact that the FAA - which is trying to show its independence from the US group - has sent the builder new questions, Elwell said.

Once Boeing has submitted all the documentation to the regulator, it will have to go through other steps: the FAA will for example perform a flight test and a thorough analysis to test the safety of the aircraft.

"It could take a month, two months or more (...) it depends on what our analysis will say," said Dan Elwell Thursday CNBC.

In addition, the FAA still has not determined what will be the proper training for the pilots, according to Dan Elwell.

The United States and a large number of countries of which Canada diverges on this point: the first ones consider that a training on computer or iPad is sufficient for experienced pilots when Ottawa wants to oblige the passage of the pilots in simulator of flight.

The European Union via EASA (European Aviation Safety Agency), Canada or Brazil have already indicated that they will make their own assessment of the MCAS patch.

China, the first country to have grounded the 737 MAX, is also a stranger in the midst of renewed trade tensions between Beijing and Washington.

- Need for transparency -

Nearly sixty representatives from thirty-three countries, where the 737 MAX flew before being grounded more than 70 days ago, accepted the invitation of the FAA, whose credibility was severely dented in this case. .

Dan Elwell and his teams will try, during the meeting, held in camera on an FAA website, to play "transparency" by explaining to their peers the security features on which they will evaluate the modified 737 MAX.

They will also detail their procedures and sought the advice of their counterparts.

"We are going to discuss how best to make the whole (re-certification) process transparent and how to regain the trust of the general public," Elwell said.

The return of confidence will be long, surveys conducted by Southwest showing that a large number of passengers are not ready to board a 737 MAX right away.

And the pilots, one of the pillars, with the flight crews, on which the companies, Boeing and the FAA intend to rely do not seem willing to sign a blank check.

"Before the MAX returns to service: we need answers and transparency," responded Thursday ECA, the European Federation of pilots, targeting the design and philosophy of this aircraft.

Beyond reputation, the 737 MAX crisis has a significant financial cost while this aircraft accounted for nearly 80% of the order book at the end of April.

Boeing, which has suspended deliveries, no longer collects money from airlines that it will also compensate for their shortfall.

"There are also additional costs related to changes in maintenance, procedures and crew training," said Michel Merluzeau.

? 2019 AFP