New York (AFP)

Six months after being grounded following two accidents that killed 346 people, the Boeing 737 MAX could return to the skies in stages due to a lack of consensus among civil aviation authorities.

Dennis Muilenburg, Boeing's CEO, said Wednesday that the plane could return to service in the US at first, before being reopened in other countries later.

"A gradual lifting of the flight ban is a possibility," said the big boss at a conference in Laguna Beach, California, during which he repeated that Boeing still planned a return to service of his plane featured at the "beginning of the fourth quarter", that is to say in October.

"Do you see a scenario where the United States decides to unilaterally lift the flight ban without the support of other regulators?", He was specifically asked.

"Yes," replied Muilenburg, adding however that the US Federal Aviation Agency, the FAA, worked with its peers, such as the European Civil Aviation Agency (EASA) or Canadian regulators, Brazilian and Chinese.

Washington was the last country to ground the MAX after the crash of a plane of this type of Ethiopian Airlines that killed 157 people south-east of Addis Ababa on March 10.

The hesitations of the US authorities had raised questions about the close relations between the FAA and Boeing, to whom the regulator had entrusted the certification of a large part of the plane following a procedure set up in 2005.

According to the experts, this mistrust threatens the rule of tacit reciprocity that has prevailed in the civil aviation industry in terms of approval of aircraft. This one wants that the green light given by the country of origin of the constructor is followed by its peers.

- Simulator or iPad? -

The situation has changed.

EASA wants to examine Boeing's changes to the 737 MAX this time to decide whether to lift the flight ban.

For the moment, it considers Boeing's solution to the possible failure of the "Angle of attack" (AOA) sensors transmitting information to the MCAS anti-stall system, implicated in the two Ethiopian accidents. Airlines (157 dead) and Lion Air (189 dead).

"EASA has been asking questions and we are answering them, I do not think they are divisive issues, I think these are questions that need to be answered because they are part of "approval process," said Dennis Muilenburg on Wednesday.

Another very sensitive point of difference is the training of pilots, of which Canada has made a priority.

Canadians, like Europeans, require simulator training, while the Americans consider it sufficient a simple computer training or iPad pilots run in the NG, version before the MAX.

"The mandatory training for MAX is a 24-day program, which is mainly simulator-based," said Muilenburg. "It's a diet turned strongly towards simulator training".

The only problem is that for the moment there are only two MAX simulators in North America, one owned by Boeing in Miami and another owned by Air Canada.

US airlines Southwest and American Airlines, big customers of the MAX, do not have any for the moment and said Boeing had told them that there was enough NG simulator training until the Ethiopian Airlines accident.

Boeing, who has already completed the changes to the MCAS and is finalizing the changes requested on the flight control system, claims to be in discussion with the Europeans on the training.

Mr Muilenburg acknowledged that country-specific requests "are creating uncertainty about the MAX's return to service schedule," whose production has been reduced to 42 copies per month, up from 52 previously. Boeing dropped a 57-unit rate increase and suspended deliveries.

© 2019 AFP