Boeing expects its troubled 737 Max aircraft to return to the skies within weeks – and before the end of the year.

Just hours after Indonesian investigators told victims’ families on Wedesday that mechanical and design issues contributed to the crash of a Lion Air 737 Max jet last October – leaving 189 dead – the company said it had developed training and software updates for its flagship aircraft.

Boeing “continues to work with the FAA and global civil aviation authorities to complete remaining steps toward certification and readiness for return to service”, it revealed in its third-quarter report on Wednesday (Chicago time).

Boeing said regulators in each country would determine how and when the planes returned to service. But the company had assumed that regulatory approval would begin in the fourth quarter of 2019 and build from there.

The construction rate of the Max aircraft – which has been hit hard by the planes’ global grounding – would build from 42 a month to 57 by late 2020, the Seattle manufacturer said.

Air regulators around the world grounded Boeing Maxes after two deadly crashes within months – the Lion Air fatality in October 2018 and an Ethiopian Airlines tragedy that killed all 157 on board in April.

It has since been revealed that a software fault contributed to triggering a system called MCAS, which was activated on both the fatal flights. It was designed to prevent the planes stalling but erroneous data led instead to them diving into the ground.

“Our top priority remains the safe return to service of the 737 Max, and we’re making steady progress,” Boeing president and chief executive Dennis Muilenburg said.

On Wednesday, Indonesian investigators confirmed to victims’ families that mechanical and design problems were behind the deadly Lion Air crash.

In a briefing ahead of the release of their final report, they said contributing factors to the crash of Lion Air’s new Boeing jet included incorrect assumptions about how the anti-stall stall device functioned and how pilots would react.

Reliance on a single angle-of-attack sensor made the system more vulnerable to failure, while the sensor on the plane that crashed had been miscalibrated during an earlier repair, investigators said.

A Boeing spokeswoman declined to comment on the briefing, saying, “as the report hasn’t been officially released by the authorities, it is premature for us to comment on its contents”.

A Lion Air representative also declined to comment.

Boeing, which has been hit hard financially by the grounding, has been under growing pressure to explain what it knew about 737 Max problems before the jets entered service.

That pressure has grown following a Reuters report about messages from a former test pilot describing erratic software behaviour on the 737 Max jet two years before the Lion Air and Ethiopian Airlines crashes.

-with AAP