April 11 (UPI) -- Airlines have tested Boeing's fix for its 737 Max jetliners -- after two deadly crashes -- 96 times, company CEO Dennis Muilenburg said Thursday.
Speaking at a leadership forum at the George W. Bush Presidential Center in Dallas, Muilenburg said about two-thirds of the 50 customers with 737 Max aircraft have tested the new software using a flight simulator. The tests amount to about 159 hours of flying time.
The software update is meant to fix the planes' automatic anti-stalling system, which could be to blame for two deadly crashes over the past six months.
Investigators said they found key evidence that strongly suggests a link between the two crashes. They found a device called a jackscrew, which controls the angle of the plane's horizontal stabilizers. The stabilizers were found in the upward position, which would have forced the nose of the plane down.
Muilenburg said Boeing engineers worked out how problems with the automatic anti-stalling system could have caused the planes to have "erroneous" sensor readings. He said the crashes proved there needs to be more improvement at Boeing.
"Lives literally depend on the work we do," he said. "We're humbled and we're learning."
Earlier this month, Boeing announced it will temporarily manufacture fewer 737 Max airplanes, dropping production from 52 to 42 per month.