The FAA has ordered Boeing 737 Next Generation operators to replace engine strut fluid draining systems with updated assemblies designed to eliminate a wear problem that caused some tubes to fail, creating a fire hazard.

The airworthiness directive (AD 2012-23-08), issued yesterday, gives operators until Dec. 31, 2017, to replace aft fairing drain tube assemblies and support clamps with improved parts designed by Boeing. The manufacturer recommends the repairs in a November 2011 service bulletin.

The wear problem surfaced more than five years ago and was the subject of a 2008 FAA directive. However, Boeing soon discovered that the modified assemblies—tubes and supporting hardware installed inside the fairing running above and parallel to each engine’s exhaust nozzle—were still causing wear, particularly around an area where a clamp meets the drain tube.

Boeing reworked the fairing drain tube assembly to include integrated support clamps.

The FAA estimates the cost of the work on the 1,098 U.S.-registered aircraft affected by the AD is $13,500.