UPDATE 1-Boeing CEO says two thirds of MAX customers have tested software fix

Boeing Co Chief Executive Dennis Muilenburg said on Thursday that 67 percent of its more than 50 737 MAX customers have tested the manufacturer's software fix in simulator sessions, with additional tests expected in the coming weeks. Boeing is under pressure to deliver an upgrade to software that is under scrutiny in two fatal crashes within five months and convince global regulators that the aircraft, which was grounded worldwide in March, is safe to fly again.

Speaking at a leadership forum in Dallas, Muilenburg said the Boeing team had made 96 flights totaling a little over 159 hours of air time with the updated software. "They will conduct additional tests and production flights in the coming weeks and we continue to demonstrate that we've identified and met all certification requirements," he said.

Muilenberg's comments come a month after the second crash, which has thrust the world's largest airplane manufacturer into its biggest crisis in years. A Lion Air 737 MAX crashed in Indonesia on Oct. 29, killing all 189 people on board. An Ethiopian Airlines jet of the same model crashed minutes after takeoff on March 10, killing all 157 on board.

"We know every person who steps aboard one of our airplanes places their trust in us. We'll do everything possible to earn and re-earn that trust and confidence from our airline customers and the flying public in the weeks and months ahead," he said. Last week Boeing cut its monthly 737 production by nearly 20 percent, signaling it did not expect aviation authorities to allow the plane back in the air anytime soon.

Chicago-based Boeing has not received any new orders for the 737 MAX since the crash in March, when deliveries also sank for the previously fast-selling aircraft. The 737 MAX has been considered the likely narrowbody workhorse for global airlines for decades to come. There were more than 300 MAX jetliners in operation at the time of Lion Air crash and about 4,600 more on order.

Muilenberg, who began his career at Boeing in 1985, became CEO in July 2015 and chairman of the board in March 2016. (Reporting by Eric M. Johnson Additional reporting and writing by David Shepardson in Washington and Tracy Rucinski in Chicago Editing by Caroline Stauffer and Susan Thomas)

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