Boeing’s 737 MAX jets will likely stay grounded for several weeks more.
The Federal Aviation Administration said ‘additional work’ is needed to Boeing’s software update.
The FAA said it would be subjected to a ‘rigorous safety review’.
The agency is taking no chances after heightened scrutiny on its hands-off policy on certifying aircraft for safety.
"The FAA will not approve the software for installation until the FAA is satisfied with the submission," an agency statement said.
The agency expects several more weeks before this is achieved.
"The FAA expects to receive Boeing’s final package of its software enhancement over the coming weeks for FAA approval. 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."
Boeing said it ‘will take a thorough and methodical approach’ and expects the software update to be completed in the ‘coming weeks’.
The FAA became virtually the last agency to ground the jets on March 13, citing similarities between the Lion Air flight that crashed in October and the Ethiopian Airlines flight that went down shortly after takeoff on March 10.
