The U.S. Federal Aviation Administration has identified a new potential risk on its Boeing 737MAX aircraft, the agency said on Wednesday.
Two people briefed on the matter told Reuters that an FAA test pilot during a simulator test last week was running scenarios seeking to intentionally activate the MCAS stall-prevention system.
During one activation it took an extended period to recover the stabilizer trim system that is used to control the aircraft, the people said.
It was not clear if the situation can be addressed with a software update or if it is a microprocessor issue, but Boeing has told the FAA it believes the issue can be addressed with a software upgrade.
The new issue means Boeing will not conduct a certification test flight until July 8 at the earliest, the sources said, and the FAA will spend at least two to three weeks reviewing the results before deciding whether to return the plane to service.