NEW YORK • Even as Boeing inches closer to getting the 737 Max back in the air, new problems with the plane are emerging that go beyond the software that played a role in two deadly crashes.
As part of the work to return the Max to service, the company and regulators have scrutinised every aspect of the jet, uncovering new potential design flaws.
At the request of the Federal Aviation Administration (FAA), Boeing conducted an internal audit last month to see if it had accurately assessed the dangers of key systems, given new assumptions about how long it might take pilots to respond to emergencies, said a senior engineer at Boeing and three sources.
Among the most pressing issues discovered were previously unreported concerns with the wiring that helps control the tail of the Max.
The company is looking at whether two bundles of critical wiring are too close together and could cause a short circuit.
A short in that area could lead to a crash if pilots did not respond correctly, the sources said.
The company informed the FAA about the potential vulnerability last month, and Boeing's new chief executive discussed possible changes to the wiring during an internal conference call last week, according to one of the sources and the Boeing engineer, who spoke on the condition of anonymity.
Boeing may eventually need to look into whether the same problem exists on the 737 NG, the predecessor to the Max. There are about 6,800 of those planes in service.
The emergence of new troubles with the Max threatens to extend a crisis that is consuming one of America's most influential companies and disrupting the global aviation business.
The Max has been grounded since last March, after two crashes killed 346 people.
The crashes were caused in part by new software on the Max that triggered erroneously and sent the planes into nosedives.
Boeing has developed a fix for the software, but it has not yet been approved, and the process of returning the plane to service has taken much longer than Boeing expected.
The Max is Boeing's most important plane, with about 5,000 ordered by airlines around the world.
But, as the grounding has dragged on, Boeing said it would temporarily shut down its 737 factory.
Regulators have suggested that the Max could be approved to fly again by spring.
The company says that even if it needs to fix the wiring issue, it would take only one to two hours per plane to separate the wiring bundles on the Max.
The engines on the Max have also become a focus of scrutiny for regulators. CFM International, the joint venture between General Electric and Safran that manufactures the engines, has told the FAA that it discovered a possible weakness in one of the engines' rotors, which could cause the part to shatter.
The likelihood of that failure is remote and regulators are not requiring an immediate fix, though they are looking to require that airlines inspect as many Max engines as possible before the plane returns to service, an FAA official said.
Boeing also recently told the FAA that it had discovered a manufacturing problem that left the plane's engines vulnerable to a lightning strike.