The problem, which hasn’t been previously reported on, has been the focus of weeks of engineering analysis, simulator sessions and flight testing by the plane maker and American air-safety officials, according to people familiar with the details.
Turning the crank moves a horizontal panel on the tail, which can help change the angle of the plane’s nose. Under certain conditions, including at unusually high speeds with the panel already at a steep angle, it can take a lot of force to move the crank in certain emergencies. Among other things, the people familiar with the details said, regulators are concerned about whether female aviators—who typically tend to have less upper-body strength than their male counterparts—may find it difficult to turn the crank in an emergency.
The analysis has been further complicated because the same emergency procedure applies to the generation of the jetliner that preceded the MAX, known as the 737 NG. About 6,300 of these planes are used by more than 150 airlines globally and they are the backbone of short- and medium-range fleets for many carriers.