Incident Overview
On September 17, 2011, at approximately 1045 central daylight time, an Airbus Industrie A320, registration C-FGYL, sustained minor damage when the copilot’s window cracked during cruise at flight level 340 northwest of Chicago, Illinois. The flight crew declared an emergency and diverted to Chicago O'Hare International Airport (ORD), landing at about 1113 without further incident. No injuries occurred among the 2 flight crewmembers, 4 cabin crewmembers, and 134 passengers. The aircraft was registered to GECAS and operated by Air Canada as flight 791 under Part 129 as a scheduled international passenger flight. Day visual flight rules conditions prevailed, and the flight operated on an activated instrument flight rules flight plan. The flight had originated from Toronto Pearson International Airport at about 0940 and was destined for Los Angeles International Airport.
Windshield Failure Details
According to the operator’s incident report, an 18-inch-long crack developed in the first officer’s windshield, extending from the left bottom corner to the top right corner, during cruise. The crack subsequently progressed into multiple multidirectional cracks that obscured the first officer’s view. The flight crew, unable to determine the severity or how many plies were affected, complied with the quick reference handbook guidance and diverted to ORD, performing an overweight landing and taxiing to the gate.
The incident windshield, part number NP-165311-8 with serial number 07169H9453; CA122417, was made from laminated glass. Its layers, from outboard to inboard, included a Herculite II glass layer coated with a Nesatron anti-ice system and associated conductive bus bar, a urethane interlayer, a vinyl interlayer, a urethane interlayer, a Herculite II glass layer, a vinyl interlayer, and a Herculite II glass layer.
Postincident Examination
A NTSB aircraft structures and maintenance specialist oversaw a postincident examination of the windshield at PPG Industries, Inc., near Huntsville, Alabama, on March 9, 2012. The examination revealed that the fracture origin was located at the center of the windshield. An area of arcing was located along the electrical bus bar at the lower edge of the windshield, near the forward corner. This location coincided with the area where the power and sensing element wires were routed around the structural glass plies. The arcing was surrounded by a cloudy and degraded interlayer, consistent with the presence of moisture. The moisture seal was worn, and its upper edge had been repaired. The forward and lower edges of the moisture seal appeared to be in factory condition.
Related Information
The latest windshield revisions produced by PPG Aerospace, with part numbers NP-165331-1/-2, are now available and include enhancements to reduce moisture ingress and its subsequent effects on the electrical system. According to the Accredited Representative from the Bureau d’Enquêtes et d’Analyses (BEA), Airbus had issued a Flight Operation Telex (FOT) on May 25, 2011, to inform operators about a revised Cockpit Windshield/Window Cracked operational procedure. The new procedure instructed crews to check if the inner ply is affected by the crack using a pen or fingernail; if the inner ply is not cracked, based on the fail-safe design, the flight crew could continue the flight without other restriction.