- Boeing's 737 Max has been grounded for nearly a year.
- The FAA has called wiring bundles in question on the planes — an added wrinkle in the planes' return — are "not compliant."
- Boeing says the FAA's assessment does not change its estimate that the 737 Max will return to service midyear.
The Federal Aviation Administration has formally rejected Boeing's proposal that it not modify nor move wiring bundles in 737 Max airplanes, according to people familiar with the decision. Boeing says the bundles do not pose a potential safety threat. Nevertheless, the FAA has told the company the bundles are "not compliant."
"The FAA continues to engage with Boeing as the company works to address a recently discovered wiring issue with the 737 Max," said a spokesman for the agency. "The manufacturer must demonstrate compliance with all certification standards. The aircraft will be cleared for return to passenger service only after the FAA is satisfied that all safety-related issues are addressed."
A spokesperson for Boeing told CNBC: "We remain in ongoing discussions with the FAA on the wire bundles. Regardless of the final determination on this matter our estimate for a mid year return to service of the MAX is unchanged."
Boeing has long contended the bundles have not created any safety issues and the same placement of the wiring in previous generations of the 737 has resulted in no issues after more than 200 million hours of flight. Still, technical staff with the FAA and the European Union Aviation Safety Agency have raised questions about the potential for the wiring bundles to short-circuit.
The concern is a short circuit in particular wiring bundles in the Max could, in certain situations, lead to pilots losing control of the plane.
If Boeing is forced to modify the Max wiring bundles, the company says it will not change its target for the Max to be ungrounded by the middle of the year. The Max has been grounded since March 2019 after two crashes, including one in Indonesia in October 2018 and another in Ethiopia in March of last year, killed all 346 people on the flights.
Boeing has maintained that any changes it is required to make to wiring bundles would take place when the company updates more than 400 Max planes that have been built but not yet delivered. The company says it plans to start delivering those planes later this year after the FAA and regulators around the world clear the Max to return to service.
Last week, at an aviation conference in Washington, D.C., FAA Administrator Steve Dickson said a certification flight to test and validate changes made to the software and procedures for 737 Max would likely take place "in the next few weeks."
A successful certification flight is one of the key hurdles Boeing must clear before the plane can be ungrounded.