The Federal Aviation Administration is looking at a potentially "catastrophic" issue with wiring that helps control the tail of the 737 Max, CBS News has confirmed. The safety review was first reported by the New York Times and confirmed by Boeing officials.

It grew out of an FAA request to Boeing for an internal audit to confirm the company had accurately assessed the dangers of key systems in light of new assumptions about pilot response times to emergency situations. 

Boeing is reviewing whether two bundles of "critical wiring" are too close together and could cause a short circuit.  


If a short goes unnoticed by pilots who then do nothing to respond to the situation, it could put the plane in a catastrophic nose dive. But multiple sources tell CBS News Transportation Correspondent Kris Van Cleave that is a hypothetical at best, since Boeing hasn't determined whether that scenario could actually occur in flight.


If necessary, Boeing would have to separate or better insulate those bundles on the roughly 800 737 Max aircraft it has built. A Boeing official tells Van Cleave that the work, if needed, could be done during the process of returning the grounded planes to flight. A fix would take an hour or two per plane, according to sources. 

Boeing hasn't determined whether it needs to look at the approximately 6,800 737NGs (previous generation 737s) currently in service, as well. 

 
Boeing informed the FAA of the issue in December and possible wiring changes were discussed in an internal conference call last week. 

From Boeing's standpoint, such an issue isn't unusual or "a major issue" and isn't unique to Boeing or the 737, but it could delay the Max's return to service.

The engine supplier for the 737 Max, CFM International, has also alerted the FAA to a potential weakness with one of the engine's rotors that has a remote possibility of a failure. The agency may require additional engine inspections. CFM is a joint venture between General Electric and the French aerospace company Safran.

Boeing is also looking at a manufacturing issue with some engine covers that involves possible damage to a coating that insulates the engine cowlings from lighting strikes. 

 
Meanwhile, the FAA confirms it's still reviewing the findings from a round of simulator testing by a cross section of 737 pilots from American, Southwest, United and Aeromexico airlines. They successfully landed the plane and responded to scenarios presented but about half didn't use the prescribed emergency procedures to handle the problems. 

The next round of FAA flight testing is expected later this month. 

Those findings could push the FAA to recommend additional simulator training but it's premature to speculate on that.

First published on January 6, 2020 / 11:39 AM

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Kris Van Cleave
Kris Van Cleave is the transportation correspondent for CBS News.