Boeing and the FAA are looking into an issue that involves part of the 737MAX wiring loom where two separate cable groups are too close together.
Issues around cable proximity are years old, going back to the discovery of electricity. With resistance and electro-magnetic impedance from cable groups – largely where cabling isn’t shielded by isolator materials – causing poor responses, unintended signals or misinterpretation of signalling by onboard systems.
These are basic electronics and such issues have caused fires from over heating and arcing, never mind cables that chaff and connect physically with worrying consequences.
The cables involved are wiring bundles that connect to the motor that controls the horizontal stabilizer and could force the aircraft to pitch up or down should a short circuit occur.
Depending on the issue, it may be a simple shielding problem, or require re-routing in the structure – either way it’s hours of work and costs – even if it just comes down to inspection.
Delays to return to service seem inevitable and it will also mean a change to the manufacturing process when the MAX goes back into production.
And that’s not the end of it, by all accounts the same issue has been found with the 737NG versions. Boeing’s new CEO is said to have been involved in conference calls discussing the breadth of the problem and how to manage it over Christmas and New Year.