Boeing had said it intended to present the US Federal Aviation Administration with the software for approval by last week. That schedule appears to have been pushed back.
"The FAA expects to receive Boeing's final package of its software enhancement over the coming weeks for FAA approval,"the agency said Monday in an emailed statement.
"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."
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The FAA also said that it will subject Boeing's upgraded software for the Max models to"a rigorous safety review."
"The FAA will not approve the software for installation until the FAA is satisfied with the submission,"the agency said in the statement.
Boeing will also have to convince skeptical regulators in Canada,Europe,China and elsewhere of the system's safety.