Even as Boeing inches closer to getting the 737 Max back in the air, new problems are emerging that go beyond the software that played a role in two crashes.

As part of the work to return the Max to service, the company and regulators have uncovered new potential design flaws.

At the request of the Federal Aviation Administration (FAA), Boeing conducted an internal audit in December to determine whether it had accurately assessed the dangers of key systems given new assumptions about how long it might take pilots to respond to emergencies, according to a senior engineer at Boeing and three people familiar with the matter.


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 people said.


Boeing is still trying to determine whether that scenario could actually occur on a flight and, if so, whether it would need to separate the wire bundles in the roughly 800 Max jets that have already been built.


The firm says that the fix, if needed, is relatively simple.


Boeing informed the FAA about the potential vulnerability last month. It 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 threatens to extend a crisis that is disrupting the global aviation business. The Max has been grounded since March, after the two crashes killed 346.


The crashes were caused in part by the MCAS software that triggered erroneously and sent the planes into nose dives. Boeing has developed a fix, but it has not yet been approved.


The new issues pose additional challenges for Boeing’s leadership. Last month, the board fired the chief executive, Dennis A Muilenburg. He is being replaced on an interim basis by Greg Smith, the former chief financial officer. Next week, David Calhoun, until recently the non-executive chairman, will take over as CEO.


Boeing is looking at raising additional debt to help bolster its resources, Dow Jones reported on Monday. Boeing had $20 billion in available funds at the end of the third quarter.