Eric M. Johnson, David Shepardson

SEATTLE/WASHINGTON (Reuters) – Boeing Co (BA.N) plans to separate 737 MAX wiring bundles, flagged by regulators as potentially dangerous, before the jet returns to service, two people familiar with the matter told Reuters on Wednesday.

The changes mark a reversal from the U.S. planemaker’s initial recommendation to the Federal Aviation Administration and pose a fresh hurdle to the jet’s already-delayed return to service.

The FAA and Boeing first said in early January they were reviewing a wiring issue that could potentially cause a short circuit on the 737 MAX, and in certain remote circumstances lead to a crash if pilots did not react in time.

On Wednesday, FAA chief Steve Dickson confirmed that the agency had rejected Boeing’s proposal to leave wiring bundles in place and said the decision on next steps was up to the planemaker.

Pending final approvals from the FAA, Boeing will move to physically separate the wiring before the MAX is cleared for service, two people familiar with the matter said.

Boeing does not view the retrofits as delaying the plane’s estimated return to service in the middle of the year, one of the people added. Boeing expects changes to take roughly one week per aircraft, but it will do some of the work as it goes through the process of removing aircraft from storage, he said.

Representatives for Boeing and FAA declined to comment.

Reporting by Eric M. Johnson in Seattle and David Shepardson in Washington; Editing by Sandra Maler and Cynthia Osterman