Boeing and the US aviation regulator say the troubled aircraft manufacturer needs more time to complete changes to a flight-control system suspected of playing a role in two deadly crashes.

The US Federal Aviation Administration said on Tuesday that it expected to receive Boeing’s proposed software enhancement package for the grounded 737 Max “over the coming weeks” after the company had previously said it planned to submit the fix for government approval by last week.

FAA spokesman Greg Martin said time was needed for additional work “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 offered the same timetable for the software fix as it works to convince regulators solve the problem.

“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 spokesman Charles Bickers said.

The company said on Monday it was continuing to work with the FAA and other regulatory agencies on certification of the update.

As well as the FAA, Boeing needs approval from other aviation regulators, including in Europe and China, where safety officials have indicated they will conduct their own reviews.

The 737 Max planes have been grounded around the world since mid-March.

The mass groundings followed the death of all 157 people on board an Ethiopian Airlines flight on March 10.

An examination of the Ethiopian Airlines black box data showed similarities to a Indonesian Lion Air crash in October 2018 that killed all 189 passengers and crew. Both planes were Boeing 737 Max jets.

Boeing said last week it had reprogrammed software on its 737 Max passenger jet to prevent erroneous data from triggering an anti-stall system, which is under mounting scrutiny following the two deadly nose-down crashes.

With the new software installed, the anti-stall system would kick in only after sensing a problem.

It would also be disabled if two airflow sensors that measure the angle of the wing to the airflow offer widely different readings.

-with AAP