Boeing has said it needs more time to finalise a software upgrade for the grounded 737 Max plane.
The aircraft manufacturer has been working to update a stall-prevention system linked to two fatal crashes in five months.
A fix has already been issued, but Boeing has now confirmed the update will not be ready to enter service until the “coming weeks”.
Boeing had been expected to submit final paperwork for the revamp to the Federal Aviation Administration – which belatedly grounded the plane last month – at the end of March.
However, even that deadline would have marked the start of testing for the new system, which is now not expected to enter service in the near future.
“We are working to demonstrate that we have identified and appropriately addressed all certification requirements and will be submitting for FAA review once completed in the coming weeks,” Boeing said in a statement.
“Safety is our first priority, and we will take a thorough and methodical approach to the development and testing of the update to ensure we take the time to get it right.”
Boeing is working on an update to the manoeuvring characteristics augmentation system, which has been implicated in the crashes of planes operated by Lion Air and Ethiopian Airlines.
There were no survivors from either incident.
It is currently believed the system forced the nose of the two Boeing 737 Max planes down, against the wishes of pilots, causing the disasters.
“The FAA expects to receive Boeing’s final package of its software enhancement over the coming weeks for FAA 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.”