Boeing 737 Max aircraft may be grounded longer than first expected after the US aviation regulator said “additional work” was needed to fix a software issue.

The Federal Aviation Administration expects to receive a final version of the update in the “coming weeks”.

Manufacturer Boeing previously indicated that the software fix would be submitted by the end of March.

But in a statement issued yesterday, the FAA 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.

“Upon receipt, the FAA will subject Boeing’s completed submission to a rigorous safety review.

“The FAA will not approve the software for installation until the agency is satisfied with the submission.”

Boeing responded by saying it was “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.

“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.”

The disclosure follows Tui issuing a profits warning on Friday due to the grounding of 15 Boeing 737 Max aircraft in its Europe-wide fleet and a further eight aircraft previously due to be delivered by the end of May.

Boeing 737 Max aircraft were grounded worldwide after last month’s Ethiopian Airlines crash which killed 157 people. This followed an Indonesian Lion Air 737 Max disaster in which 189 people were killed.

The European Aviation Safety Agency told the Financial Times earlier on Monday that it was in “permanent contact” with both the FAA and Boeing regarding the review of the 737 Max.

The European civil aviation safety regulator said it was “working towards having the aircraft return to service as soon as possible, but only once there is complete reassurance that it is safe”.

“This includes, as stated at the European Parliament, that Easa will go in-depth of the proposed changes that may include design and training aspects,” a spokesperson added.

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