Washington, Apr 18 (IANS): Boeing CEO Dennis Muilenburg has said the company was making "steady progress" toward certification of a software update for the 737 MAX aircraft, grounded worldwide following two crashes within five months.

"We're making steady progress on the path to certification for our 737 MAX software update, thanks to the work of our Boeing pilots, engineers and technical experts," Muilenburg said in a video posted on Twitter on Wednesday.

In the video, where he is standing in front of a 737 MAX plane at Boeing Field in Seattle, the CEO said the company carried out flight test of the updated software with its technical and engineering leaders on board the airplane on Tuesday.

"That was the final test flight prior to the certification flight," he said.

Boeing's test pilots, he said had conducted 120 flights, amounting to 203 hours of airtime, with the anti-stall software fix for the Manoeuvering Characteristics Augmentation System (MCAS).

Muilenburg also said he participated earlier on Wednesday in another demonstration flight and witnessed this software's operating in its final form as designed across a range of flight conditions.

"Around the world more than 85 per cent of our 50-plus MAX customers and operators have now experienced the new software through a series of simulator sessions," said the Boeing CEO.

Boeing is working desperately on the software update of MCAS of 737 MAX aircraft, one of which crashed in October 2018 and other in March this year, killing 346 people on board.

Investigators have zeroed in on the MCAS flight control system as a possible factor behind the two tragedies. Many countries, including the US, grounded the aircraft after the March crash.