Boeing needs to undertake additional work on its proposed fix to the 737 Max before it can be submitted for US review, a Federal Aviation Administration official said Monday.
Boeing's top-selling MAX jet was grounded around the world last month after two fatal crashes. "There were no 737 max flying in the kingdom at the time and there aren't plans for them to be back in the near future", according to Transport Minister Nabeel al-Amudi. "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".
The FAA said last week will increase oversight by this summer.
The FAA says once it gets Boeing's completed proposal, it will conduct a rigorous safety review.
More than 300 Boeing 737 MAX jets have been grounded worldwide after two crashes - in Indonesia in October and in Ethiopia last month - killed almost 350 people.
Boeing designed the automated MCAS system - which lowers the aircraft's nose if it detects a stall or loss of airspeed - for this particular model.
Chicago-based Boeing is under intense scrutiny after two crashes since October killed 346 people.
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Earlier Monday, Ethiopian foreign ministry spokesman Nebiat Getachew had said his country's transport ministry would release "a preliminary report into its investigation" of the March 10 accident in which a Nairobi-bound Boeing 737 MAX crashed shortly after taking off from Addis Ababa.
In Vietnam, Bamboo Airways agreed to buy as many as 26 narrow-body jets from Airbus SE, just a month after saying it was considering ordering as many as 25 Boeing 737 Max planes.
That was the second related piece of evidence to emerge from the black boxes of the Ethiopian flight after an initial sample of data recovered by investigators in Paris suggested similar "angle of attack" readings to the Lion Air crash.
A source with knowledge of the investigation has said an anti-stalling system, the Maneuvering Characteristics Augmentation System (MCAS), was activated shortly before the crash.
One pilot, according to the Wall Street Journal, said to the other "pitch up, pitch up!" before their radio died.
Ethiopia has already said there were "clear similarities" between the two MAX 8 crashes.
As the company finalises a software upgrade for the grounded 737 Max, it's fighting to hang onto some customers whose confidence in the best-selling jet has been shaken.