The Associated Press

Boeing said Tuesday that it doesn’t expect federal regulators to approve its changes to the grounded 737 Max until this summer, several months longer than the company was saying just a few weeks ago.

That timetable — the latest of several delays in the plane’s approval process — will create more headaches for airlines by pushing the Max’s return further into the peak summer travel season or possibly beyond it.

Boeing shares fell nearly 6% at one point, to a 52-week low, and closed down 3.4%.

The company said regulators will decide when the Max flies again but that it periodically gives airlines and suppliers its best estimate of when that will happen.

“This updated estimate is informed by our experience to date with the certification process,” Boeing said in a statement. “It is subject to our ongoing attempts to address known schedule risks and further developments that may arise in connection with the certification process. It also accounts for the rigorous scrutiny that regulatory authorities are rightly applying at every step of their review” of the plane’s flight controls and pilot-training requirements.

The latest timetable is based on work remaining to be done before the Federal Aviation Administration will allow the Max back in the sky including work on flight-control computers, according to two people familiar with the matter, who spoke on condition of anonymity to discuss details that Boeing did not provide.

The FAA said in a statement that it is conducting “a thorough, deliberate process” to make sure that Boeing’s changes to the Max meet certification standards. The agency said, as it has for months, that it has no timetable for completing its review.

The three U.S. airlines that own Maxes — Southwest, American and United — have scrubbed the plane from their schedules until early June. It is possible, however, that they won’t use the planes until much later, possibly after the busy summer travel season is over.

Even after the FAA certifies Boeing’s work, airlines will need several more weeks to prepare their grounded planes and train pilots. After long insisting that training could be done quickly on tablets, Boeing recently reversed course and recommended that pilots go through sessions on flight simulators before operating the plane, adding more time to airline preparations.