New York (AFP) - Nearly six months after its 737 MAX jets were grounded, Boeing is now close to applying to recertify the aircraft, according to sources, but the timeframe for flights to resume remains murky.
Regulators will have final say on when the planes to return to service, clouding the outlook, in part because of signs of discord between US and international regulators.
Boeing has completed work on an upgrade to the anti-stall system known as the Maneuvering Characteristics Augmentation System that has been linked to two crashes, said a person familiar with the matter.
But Boeing is continuing to modify the flight control system on the MAX after the US Federal Aviation Administration raised issues in late June, said another person familiar with the situation.
The latter issue can be addressed with upgrades to flight software and will not require major changes in plane hardware that are more costly and extensive, this person added.
Boeing has said previously that it expects to submit its certification package to the FAA around September, with anticipated approval around a month later.
A Boeing spokesman said the timetable for bringing the MAX back still holds.
"Our best current estimate continues to be a return to service of the MAX that begins early in the fourth quarter," the Boeing spokesperson said.
Boeing officials were to unable respond to questions on modifications made to the 737 MAX flight control system at an August meeting in Seattle with international aviation regulators, sparking fears of another delay.
The company's chief executive, Dennis Muilenburg, is expected to update investors during an appearance at an investor conference on September 11.
US regulators have said there is no set timeframe for clearing the MAX to resume service and that the planes will return to the air only after Boeing satisfies all questions on safety.
- Discord among regulators -
The timeframe for the MAX' return is already much later than Boeing had expected. The aerospace giant was close to submitting its certification application in the spring only to be ordered by the FAA to address additional questions.
That experience has left Boeing cautious about its current outlook, warning that the fourth quarter projection "reflects the company's best estimate at this time, but actual timing of return to service could differ from this estimate."
A major challenge involves the broad array of international regulators who will need to approve the MAX recertification.
The FAA could move more quickly than other regulators but US officials have said they would prefer if other aviation bodies quickly followed them.
However, the question of pilot training has divided regulators, with US officials skeptical of the need for flight simulator training for MAX pilots and European and Canadian bodies viewing it as necessary, said a person familiar with the matter.
In a presentation Tuesday, the head of European Union Aviation Safety Agency highlighted the training issue and described the matter as a "work in progress" in the agency's oversight.
The EASA presentation also said it would not delegate MAX decisions to the FAA and there was "still no appropriate response" to problems with the malfunction of the "angle of attack," which triggered the MCAS system in both crashes.
Some carriers, including Southwest Airlines and Air Canada, have already pushed back their plan for resuming MAX flights until January 2020, a timeframe that some experts consider more likely than Boeing's current outlook for the fourth quarter.
"We still think the MAX will resume in the first quarter under the best-case scenario," said Michel Merluzeau, an expert at Air Insight Research.
Alexandre de Juniac, head of the International Air Transport Association, a trade group representing airlines, said Tuesday that he is troubled by the prospects for staggered regulatory approval.
"With the 737 MAX we are a bit worried ... because we don't see the normal unanimity among international regulators," he told journalists in Chicago.
"We see a discrepancy that's detrimental to the industry" de Juniac said, adding that any changes to the certification process should be done "collectively."