Boeing’s 737 MAX return to service could drag into the latter part of the year as the company continues to address safety concerns over its best-selling single-aisle plane.

The latest uncertainty comes after a new Bloomberg News report that says Boeing now may need up to three months to fix a software issue the Federal Aviation Administration identified while conducting simulator tests on updates to the plane’s flight control system.

Bloomberg, which cites “unnamed people familiar with the matter,” cast an increasingly uncertain timeline for the jet’s possible return to service. “Estimates for how long it will take to address the issue range from a few weeks to three months,” Bloomberg wrote, citing its sources.

The Associated Press also reported on the possibly shifting MAX timeline. A Boeing official told the news agency on Thursday that the company believes it can have the needed MAX software update fixes ready for FAA approval “in the September timeframe.”

But, even if Boeing hits that target, AP notes that it could take regulators “several weeks” more to analyze the updates and then – if they’re approved – even more time for airlines to take their MAX jets out of storage and ready them for a return to passenger service. That, AP suggested, could be “a sign that the troubled jet likely won’t be flying until late this year.”

While American operators of the jet announced plans to return their 737 MAX fleets to service as early as September, it seems increasingly likely that the planes could remain grounded well into the fall.

Featured photo by Stephen Brashear/Getty Images