Efforts to get Boeing Co.’s 737 MAX jetliners back in the air have been delayed in part by concerns about whether the average pilot has enough physical strength to turn a manual crank in extreme emergencies.
The concerns have made the issue the focus of engineering analysis, simulator sessions and flight testing by the planemaker and American air-safety officials, according to people familiar with the details. The extent of the internal debate hasn’t been previously reported.
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 an unusually high speed 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 confused 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.
Neither Boeing nor regulators anticipate design or equipment changes to result from the review, these people stated. But the issue has forced a reassessment of some safety assumptions for all 737 models, as previously reported by The Wall Street Journal.
The global MAX fleet of about 400 planes was grounded in March, following two fatal nose-dives triggered by the misfiring of an automated flight-control system called MCAS. The two crashes killed a total of 346 people.
There are no plans to restrict certain pilots from getting behind the controls of any 737 models based on their strength, according to people with knowledge of the discussions. But both Boeing and Federal Aviation Administration leaders are concerned that if such discussions become public they could be overblown or sensationalized, according to industry and government officials familiar with the process.
All of the 737 MAX’s underlying safety questions have to be resolved before the FAA can put the grounded fleet back in the air, according to the U.S. and European flight officials.