AD 2021-06-03 Prompted By A Report Of A Water Supply Line That Detached At A Certain Joint

The FAA is adopting a new airworthiness directive (AD) for all The Boeing Company Model 777F series airplanes. This AD was prompted by a report of a water supply line that detached at a certain joint located above an electronic equipment (EE) cooling filter, leading to water intrusion into the forward EE bay. This AD requires deactivating the potable water system. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective March 5, 2021.

Supplementary Information: The FAA has received a report of a water supply line that detached above an EE cooling filter, leading to water intrusion into the forward EE bay, on a Model 777F series airplane with 34,000 total flight hours and 6,000 total flight cycles.

During potable water servicing on ground, the operator received multiple messages appearing on the engine indication and crew alert system (EICAS) indicating multiple affected EE line replaceable units (LRUs). Further investigation revealed that the location of a joint on a swaged end fitting ferrule of a corrosion resistant stainless steel (CRES) water supply line had become partially or fully detached from the tube, causing water to spill onto an EE cooling filter (directly below the fitting) in the left-hand sidewall at station (STA) 571. The amount and duration of the water spillage are unknown. The cooling filter became saturated with the water, which was then blown via the EE cooling system into multiple EE LRUs located in the EE bay.

Water that has been ingested or has entered into the EE cooling system via the cooling filter can be circulated to multiple EE racks and can accumulate on the LRUs, particularly where forced air cooling occurs. Water ingress to these LRUs can affect multiple EE bay racks and LRUs, resulting in loss of functionality or inaccurate output of critical electrical systems and possible loss of control of the airplane. The FAA is issuing this AD to address the unsafe condition on these products.

Model 777F series airplanes line numbers (L/Ns) 960 and subsequent have a joint at this location from the factory-installed CRES tube assembly. Boeing released Service Bulletin 777-38-0042 as an economic service bulletin providing operators with airplanes prior to L/N 960 instructions to retrofit to this configuration at their discretion.

Therefore, this AD will require deactivation of the potable water system for all 777F with this joint installed either in production or through performance of Boeing SB 777-38-0042.

FMI: www.regulations.gov