Europe’s aviation regulator will send its own test pilots and engineers to fly forthcoming certification flight tests of Boeing’s newly modified 737 MAX, the European Union Aviation Safety Agency (EASA) said Tuesday.

In addition, EASA said it favors a design that takes readings from three independent Angle of Attack sensors rather than the two-sensor system in Boeing’s proposed upgrade to the MAX.

The European agency’s stance underscores how badly the two deadly MAX crashes in Indonesia and Ethiopia have disrupted the harmony in international aviation that previously granted primacy to the U.S. Federal Aviation Administration (FAA).

In little-noted comments at the European Parliament last week, the French executive director of EASA, Patrick Ky, had pointed words for his American counterparts.

“The FAA is in a very difficult situation,” said Ky in a video of his address to the Transport committee of the European Parliament. “When they will say, this (airplane) is good to go, it’s very likely that international authorities will want a second opinion, or a third opinion.”

“That was not the case one year ago,” Ky added. “I think that’s going to be a very strong change in the overall worldwide hierarchy or relationship between the different authorities.”

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Although EASA said it’s not mandating how Boeing must address its concern over the Angle of Attack system redesign, Tuesday’s declaration that it would prefer a three-sensor system was a more specific critique than that laid out in Ky’s slide presentation last week, which said Boeing had “still no appropriate response to Angle of Attack integrity issues.”

Installation of a third Angle of Attack sensor in the MAX could be an expensive and prolonged process and might affect not only the new 737 MAX jet but the thousands of older model 737s in service around the world, which all come with just two such sensors. Boeing declined to comment.

EASA’s elaboration Tuesday of its differences with the FAA is a further sign of the differences that have emerged since the October and March crashes that killed 346 people and caused the plane to be grounded worldwide.

According to insiders, the FAA is all but set to approve Boeing’s proposed MAX redesign.

An FAA spokesman, citing the example of several Airbus jets, said, “It’s common for aviation authorities to conduct test flights of new aircraft and major derivatives that other civil aviation authorities certificate.”

The spokesman added: “We continue to work with other international aviation safety regulators and will carefully consider all recommendations. The FAA will incorporate any changes that would improve our certification activities.”

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For Boeing, any daylight between the various regulators could be a massive problem. As it moves closer to finalizing its proposed fix for the 737 MAX, it’s struggling with the deep divergence between the FAA and corresponding air safety regulators overseas, most critically EASA.

Ky told the European committee his agency’s insistence on conducting a broad new independent review of the design of all the safety-critical systems on the MAX was “not very popular with our American colleagues.”

But he said such a new review was necessary because there were parts of the original MAX design that EASA “had not completely certified ourselves, because we had delegated some of the tasks to the FAA.”

As a result, he said EASA decided “to basically re-certify the parts that are safety critical that we hadn’t looked at in the previous instance.”

He said this included but was not confined to the new flight-control system — called MCAS (Maneuvering Characteristics Augmentation System) — that was triggered in both crashes by a faulty Angle of Attack signal and repeatedly pushed down the nose of each jet until the pilots lost control.

Ky said an imminent report from an international panel of aviation-safety experts set up by the FAA to review the certification of the MAX — and representing 11 separate regulators including EASA and its Canadian and Chinese counterparts — will cast “a critical eye on this notion of delegation from the FAA to Boeing.”

This Joint Authority Technical Review (JATR) report is expected any day now, and Ky said it will have a particular focus on the system safety assessment “of this famous MCAS, which was a major, if not the major, contributor to both accidents … which had been auto-certified by Boeing.”

“Yes, there was a problem in this notion of delegation by the FAA of the MCAS safety assessment to Boeing,” Ky told the EU Parliament committee.

“This would not happen in our system,” he insisted. “Everything which is safety-critical, everything which is innovative … has to be seen by us and not delegated.”

Ky went on to say that though he respected his FAA counterparts, the prior implicit reliance on their capabilities won’t continue.

“They are working for the citizens and they have a very strong ethics … I have no doubt in the values of the FAA,” he said. “What I think will need to be changed is their methodologies and possibly as well the methodologies we use when we validate a product which has been certified by the FAA.”

That said, Ky recognized that his 800-strong agency cannot do all the certification work on Boeing planes. And even if it tried to, he said, the U.S would then want to recertify all the Airbus planes.

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“This is a duplication of effort,” Ky said. “I don’t think we can afford that. We need to find a way to work together — but bearing in mind what happened on the 737 MAX.”

Ky’s remarks reveal a deep rift that’s opened up in the world of aviation-safety regulation, one that clearly will affect how future airliners are certified.

For Boeing, the consequence is immediate: uncertainty over how soon the MAX can return to service worldwide.

In addition to the worldwide in-service fleet of 387 MAXs grounded around the globe since mid-March, Boeing has by now built and and parked another 252 of the jets.

The biggest MAX parking lot is now Moses Lake in eastern Washington, where Boeing on Tuesday landed the 100th MAX for storage until it gets approval to return to passenger service.

It’s unclear if EASA’s dissatisfaction with the MAX’s two-sensor Angle of Attack system, first reported by Bloomberg Tuesday, is a bar to the jet’s return to service or something that might be addressed longer-term.

Janet Northcote, EASA’s head of communications, said via email that while “all certified aeroplanes have a minimum of two vanes, which is considered to be the bare minimum requirement to meet the safety objectives,” the agency won’t necessarily require installation of a third Angle of Attack vane.

“We are not being prescriptive in the way these concerns should be addressed,” she wrote. “It could be through improvement of the flight crew procedures and training, or through design enhancements, or a combination of the two.”