AD NUMBER: 2011-09-11

MANUFACTURER: The Boeing Company Model 777-200 and -300 Series Airplanes Equipped With Pratt and Whitney Engines
SUBJECT: Airworthiness Directive 2011-09-11

SUMMARY: This AD requires repetitive inspections for hydraulic fluid contamination of the interior of the strut disconnect assembly; repetitive inspections for discrepancies of the interior of the strut disconnect assembly, if necessary; repetitive inspections of the exterior of the strut disconnect assembly for cracks, if necessary; and corrective action if necessary. This AD also provides an optional terminating action for the inspections.

This AD was prompted by reports of system disconnect boxes that have been contaminated with hydraulic fluid and, in one incident, led to subsequent cracking of titanium parts in the system disconnect assembly. We are issuing this AD to detect and correct hydraulic fluid contamination, which can cause cracking of titanium parts in the system disconnect assembly, resulting in compromise of the engine firewall. A cracked firewall can allow fire in the engine area to enter the strut and can lead to an uncontained engine strut fire if flammable fluid is present.

Cracking of the disconnect box may also reduce the effectiveness of the fire extinguishing system in the engine compartment and could contribute to an uncontained  engine fire. In addition, a cracked disconnect box can leak flammable fluids into the engine core, which can initiate an engine fire, and lead to one or both fire conditions discussed above.

FMI: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/6BD1591860C9A4AF862578840056A5D3?OpenDocument