FAA Finds New Problem With 737 Max Jets, Delaying Their Return To Flight

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The Federal Aviation Administration has found a new problem in Boeing's troubled 737 Max that the company must address before the regulatory agency will allow the airplanes to fly passengers again. The discovery further delays the airliner's return to service.

Southwest, American and United Airlines, the three U.S. carriers that fly Max jets, have already pulled the aircraft from their schedules through Labor Day weekend and this latest development could set back the plane's return to commercial flight well into the fall.

Boeing's popular narrow-body aircraft has been grounded since March after an Ethiopian Airlines 737 Max crashed shortly after taking off from the airport in Ethiopia's capital, Addis Ababa, killing all 157 people on board. It was the second crash of a Max plane in five months; as a Lion Air jet crashed in Indonesia last October, killing 189 people.

Investigators link both crashes, in part, to an automated flight control system that acted on erroneous information from malfunctioning sensors and put the planes into nose dives the pilots could not pull the planes out of.

Boeing has developed a software fix for that flight control system, called MCAS, but sources familiar with the situation tell NPR that in simulator testing last week, that FAA test pilots discovered a separate issue that affected their ability to quickly and easily follow recovery procedures for runaway stabilizer trim and stabilize the aircraft.

A statement from the regulatory agency says as part of a process designed to discover and highlight potential risks, "the FAA found a potential risk that Boeing must mitigate."

Boeing says in a statement that the company is working on the required software fix to address the FAA's request. A spokesman told NPR the company is committed to working closely with the FAA to safely return the 737 Max to service.

Just a few weeks ago, officials with the FAA and Boeing had suggested the 737 Max could be certified to fly airline passengers again by the end of this month. Now that timeline is being pushed back at least a few weeks, if not considerably longer.