But in recent days, the timeline was extended by several weeks.

The delay came about through the workings of Boeing’s so-called non-advocate review, a process in which Boeing employees who are not working on the software fix vet the work before it is submitted to the F.A.A., according to people with knowledge of the process who were not authorized to speak publicly.

It is not clear what specific changes the Boeing employees believe needed to be made.

On Monday, the F.A.A. made a statement acknowledging the timing had been pushed back.

“The F.A.A. expects to receive Boeing’s final package of its software enhancement over the coming weeks for F.A.A. approval,” the agency said. “Time is needed for additional work by Boeing as the result of an ongoing review of the 737 Max Flight Control System to ensure that Boeing has identified and appropriately addressed all pertinent issues.”

After the F.A.A. released its statement on Monday, Boeing also acknowledged the delay.

“Boeing continues to work with the U.S. Federal Aviation Administration and other regulatory agencies worldwide on the development and certification of the MCAS software update and training program,” it said. “We are working to demonstrate that we have identified and appropriately addressed all certification requirements and will be submitting for F.A.A. review once completed in the coming weeks.”

The 737 Max will remain grounded for at least several more weeks, prolonging a crisis that has engulfed Boeing.