Europe’s aviation regulator has outlined five major requirements it wants Boeing Co. to address before it will allow the planemaker’s 737 Max to return to service, according to a person familiar with the matter. One of them, about the jet’s autopilot function, hasn’t surfaced previously as an area of concern.

The European Union Aviation Safety Agency has sent its list to both the U.S. Federal Aviation Administration and Boeing, the person said, asking not to be identified because the details aren’t yet public. The FAA hasn’t publicly discussed details about what changes it’s demanding on the Max, so it’s difficult to know whether the EASA demands differ dramatically — and whether they would significantly boost the cost and time to get the Max back in the air.

Regulators worldwide grounded Boeing’s best-selling plane in March following two crashes in five months that killed a total of 346 people.

The issues being raised by EASA are consistent with the FAA’s own questions, said a person familiar with the U.S. agency’s work who wasn’t authorized to speak about the matter. In a statement, the FAA declined to confirm the specific matters being raised by EASA but said: “The FAA continues to work closely with other validating civil aviation authorities on our review of Boeing’s certification documentation for the 737 Max. This process involves regular communications among all parties.”

Asked about the potential impact of EASA’s concerns, Boeing issued a statement saying company officials continue “to engage with regulators and are providing information as we work towards the safe return to service for the Max.”

Autopilot Concerns

EASA’s checklist includes a number of issues that have been disclosed: the potential difficulty pilots have in turning the jet’s manual trim wheel, the unreliability of the Max’s angle of attack sensors, inadequate training procedures, and a software issue flagged just last week by the FAA pertaining to a lagging microprocessor. But the agency also listed a previously unreported concern: the autopilot failing to disengage in certain emergencies.

“Any of these could significantly affect the return to service, but we don’t know if they are actually going to become requirements or are they just items for discussion,’’ said John Cox, a former 737 pilot who is president of the aviation consulting company Safety Operating Systems.

Cox said that such questions between regulators are the norm during aircraft certification work and may not pose new risks for Boeing.

The one issue Cox said he hadn’t previously heard about involved the autopilot. Having to alter a system as complex as the 737’s autopilot could have major ramifications, he said. However, he said he isn’t aware of any underlying safety issues with the autopilot that would justify such an action.

The European regulator has found that the autopilot doesn’t always properly disengage, which could mean that pilots wouldn’t have the time to intervene before the plane begins to stall.

The EASA list excludes several other smaller issues that the agency hasn’t flagged as critical. The agency’s findings follow its broad, independent review of the 737 family’s entire flight control system that focused on the differences between the Max variant and the older “Next Generation” model, the person said. EASA opted to conduct its own assessment of the aircraft.

The review has become a critical focal point for the industry in gauging when the plane will be able to fly again, with regulators globally expected to lean on EASA’s findings. The FAA is facing multiple investigations over its handling of the original certification of the Max and the so-called Manuevering Characteristics Augmentation System that has been linked to both crashes.

It’s not clear how difficult it will be for Boeing to address the issues described above. People familiar with the matter told Bloomberg last week that the latest software problem could take as long as three months to fix. The FAA has also previously denied that the trim wheel — which is used to lift or lower a plane’s nose during an emergency — would cause delays.

Potentially more complex will be addressing the AOA, or angle of attack, sensors on which MCAS relies. At the time of the Ethiopian crash in March, Boeing’s system was using just one of the two sensors installed on the plane. EASA director Patrick Ky said in an interview last month that retrofitting additional hardware was not off the table, a measure that could be costly and time consuming for the manufacturer.

EASA, in its recommendations, stopped short of telling Boeing how to address the issues, instead asking the company to propose solutions that will then be assessed, the person said. For example, if Boeing can prove the effectiveness of a new training procedure that doesn’t include the more burdensome requirement for simulator training, it could avoid that additional expense.

Coordinating Relaunch

Both the FAA and EASA along with Canada and Brazil, have meanwhile come together in tentative agreement that the return to service should be closely coordinated in an effort to help restore public trust in the global aviation safety system, people familiar with the matter have said, though they cautioned that EASA may still make additional requests and lag behind the FAA.

A spokesman for EASA wasn’t immediately able to comment. FAA acting Administrator Daniel Elwell has said that the grounded plane won’t be returned to service until the agency can be assured it is safe and pilots are adequately trained to handle any emergencies.

Boeing has been telling customers and others in the industry that it expects the plane will be returned to service by September. That timetable includes fixing the software implicated in the two crashes as well as the latest flaw identified with the microprocessor, said a person familiar with the company’s guidance.

—With assistance from Julie Johnsson

©2019 Bloomberg L.P.

This article was written by Benjamin Katz and Alan Levin from Bloomberg and was legally licensed through the NewsCred publisher network. Please direct all licensing questions to legal@newscred.com.

Photo Credit: A Boeing 737 Max jet. The European Union Aviation Safety Agency has newly surfaced concern over the 737's autopilot function. Flickr