FAA has ordered Boeing 737NG operators to replace cockpit window anti-icing system components to minimize the risk of wire damage that caused arcing and smoke on one in-service aircraft.

The airworthiness directive (AD), issued today, gives operators until Feb. 10, 2018, to replace damaged coil cords that run along both the captain’s and first officer’s side walls. Repair instructions include inspecting coil cord connector “keyways” to ensure they are configured in a specific way and, for some aircraft, adjusting cord receptacles.

Boeing learned of the incident in 2006 and sent operators service instructions that fix the problem. Boeing then revised its recommendation to address an issue discovered during work to fix the original problem.

“Three operators accomplished this service bulletin before this [r]evision...[and] found that the wire connectors at the two ends of the coil cord rub each other,” a November 2011 update to the original bulletin explains. “The rub condition occurs when the window opens or is in the fully open position. The rub condition can possibly cause damage to the wire connector and the coil cord.”

FAA says the issue affects 712 U.S.-registered 737NGs through line no. 3798, which was delivered in October 2011. However, a Boeing service bulletin issued in April 2013 adds 75 newer aircraft to the list.

FAA declined to revamp its AD because it didn’t want to re-open the rulemaking process and further delay the directive. FAA says it may issue a related order for the newer aircraft not covered by the mandate.

The per-aircraft fix is about $2,100 if damaged cords must be replaced, FAA estimates.

Some operators have pressed forward without a mandate. Delta tells FAA that it has completed the work on its 71 affected 737-800s.