Efforts to unground Boeing’s 737 MAX jets have been delayed in part amid concerns about whether the average pilot possesses enough strength to turn a manual trim crank during emergencies, according to a new report.
Sources told the Wall Street Journal that the problem has been the focus of lengthy engineering analysis, simulator sessions and flight tests by Boeing and US air safety officials.
The manual crank moves a horizontal panel on the tail, which can help change the 737’s nose angle. Under extreme circumstances, including at very high speeds, a lot of strength is needed to move the trim device.
People familiar with the details told the newspaper that regulators also are concerned about whether female pilots — who typically have less upper-body strength than men — may find it difficult to turn the crank.
Neither the plane manufacturer nor regulators anticipate design or equipment changes to result from the review, the sources told the Journal — but the matter has forced a reassessment of some safety considerations for all 737 models.
The global fleet of about 400 MAX planes was grounded in March after two fatal nose-dives triggered by the misfiring of the automated anti-stall Maneuvering Characteristics Augmentation System, or MCAS, in Ethiopian Airlines and Lion Air MAX 8 jetliners.
All 346 people aboard both new planes were killed after the pilots lost control.
The MCAS software takes readings from two angle-of-attack sensors, which determine how much the nose is pointing up or down relative to the flow of air.
When MCAS detects that the plane is about to reach the so-called critical angle of attack, at which point the wings can no longer generate lift, the system automatically pushes the nose down.
There are no plans to restrict certain pilots from flying a 737 MAX based on their strength, people with knowledge of the deliberations told the Journal.
But both Boeing and Federal Aviation Administration leaders are worried that if such deliberations become public, they could be sensationalized, aviation and government officials familiar with the process told the paper.
A Boeing rep told the Journal: “We will provide the FAA and the global regulators whatever information they need.”
Boeing has previously said it is providing additional information about “how pilots interact with the airplane controls and displays in different flight scenarios.”
An FAA spokesman declined to comment to the paper on specifics.
Acting FAA chief Daniel Elwell has said the agency is pursuing a complete investigation of the two MAX crashes and considering everything — including emergency procedures, training and maintenance.