LE BOURGET, France — 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 plane maker 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 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.
Neither Boeing nor regulators anticipate design or equipment changes to result from the review, these people said. 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 deliberations. 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 U.S. and European aviation officials.
In response to questions, a Boeing spokesman said: “we will provide the FAA and the global regulators whatever information they need.” In the past, Boeing has said it is providing additional information about “how pilots interact with the airplane controls and displays in different flight scenarios.”
Speaking before the Paris Air Show here this week, Boeing Chief Executive Dennis Muilenburg said he wanted to conduct an “end-to-end, comprehensive review of our design and certification processes,” as well as other matters.
An FAA spokesman declined to comment on specifics. In the past, acting FAA chief Daniel Elwell said the agency is pursuing a complete investigation of the two MAX crashes and looking at everything, including emergency procedures, training and maintenance.
FAA experts also are seeking to assess how issues regarding pilot strength were dealt with during certification approvals of older versions of the 737, according to the people familiar with the specifics.
Simulator sessions and flight tests have measured the strength required to turn the crank in various flight conditions for pilots of both genders, according to two of the people briefed on the details.
In a flight-simulator test earlier this month, The Wall Street Journal’s Scott McCartney and pilot Roddy Guthrie, fleet captain for the 737 at American Airlines, experienced troubles in turning the wheel. As described in a June 5 article, Capt. Guthrie couldn’t move the wheel until Mr. McCartney pitched the plane’s nose down, easing some of the pressure on the wheel.
Government and industry experts are considering potential operational, training and pilot manual changes to resolve safety concerns, according to the people familiar with the specifics. The results are expected to be part of a package of revised software and training mandates that the FAA is seen issuing later this summer.
Capt. Chelsey “Sully” Sullenberger, the retired US Airways pilot celebrated for his 2009 “Miracle on the Hudson” landing, said Wednesday that pilots should be required to spend time in simulators before the MAX returns to service, not only to review the updates to the MCAS software but to practice situations where manually turning the crank would be more challenging. At higher airspeeds, turning the wheel could require two hands, the efforts of both pilots, or may not be possible at all, he said.
“They need to develop a muscle memory of their experiences so that it will be immediately accessible to them in the future, even years from now, when they experience such a crisis,” he told the House Committee on Transportation and Infrastructure’s aviation subcommittee during a hearing Wednesday.
Mr. Sullenberger told the committee that he recently experienced a recreation of the fatal MAX flights in a flight simulator. He came away from it understanding how crews could have been overwhelmed by alerts and warnings without enough time to fix the problem.
The pending software fix is intended to make it easier for pilots to override MCAS, which moves a horizontal panel on the tail — called a horizontal stabilizer — to point the nose down.
The emergency procedure under scrutiny is the final step in a checklist to counteract dangerous horizontal stabilizer movements that can be prompted by a range of causes including an MCAS malfunction.
The FAA’s testing comes after the agency prodded Boeing to draft a new safety assessment covering MCAS as well as the emergency procedure, according to U.S. and European aviation officials.
The FAA isn’t alone in documenting the differences in average strength between men and women in critical safety roles. The Pentagon, for example, categorizes such information in assessing the fitness of some uniformed personnel for certain assignments.