NTSB Factual Report

On May 4, 2015, about 2105 central daylight time, an Airbus A319-112, N941FR, sustained minor damage when the copilot's window cracked during cruise at flight level (FL)340 northeast of New Orleans, Louisiana. The flight crew reported smoke occurred, they declared an emergency, and diverted the flight to the Louis Armstrong New Orleans International Airport, near New Orleans, Louisiana, landing about 2136 without further incident. There were no injuries to the 2 flight crewmembers, 3 cabin crewmembers, and 131 passengers. The airplane was registered to and operated by Frontier Airlines Inc. as flight 1225, under the provisions of 14 Code of Federal Regulations Part 121 as a scheduled domestic passenger flight. Night visual flight rules conditions prevailed for the flight, which operated on an activated instrument flight rules flight plan. The flight originated from the Orlando International Airport, near Orlando, Florida, about 2002, and was destined for the McCarran International Airport, near Las Vegas, Nevada.

The operator's incident report indicated the flight had a normal departure. About an hour into the flight, at cruising altitude of FL340, the first officer, who was the non-flying pilot, pointed to his windshield. The flightcrew observed arcing and sparks along the bottom of the windshield starting from the left side going extremely fast and intensifying towards the right side. The captain was about to call for the quick reference handbook (QRH) windshield/window arcing procedure when the flightcrew heard a popping sound and observed the whole windshield cracking. The captain did not remember if there were any breakers popped or if there was an electronic centralized aircraft monitor (ECAM) message during the event. The fault ANTI ICE R WINDSHIELD was recorded during the event flight.

The incident window was removed from the airplane and shipped to its manufacturer, PPG Aerospace, Inc. (PPG), near Huntsville, Alabama, for detailed examination under National Transportation Safety Board (NTSB) oversight on August 11, 2015.

The Airbus 319 windshield, Airbus part number 6968962000, PPG Aerospace (PPG) part number NP165311, has a laminated glass configuration. The windshield is manufactured of the following materials, from the outboard surface to the inboard surface; a 3 mm thick Herculite II chemically strengthened glass pane, a PPG Nesatron conductive heating film layer for anti-ice capability, a PPG 112 urethane interlayer, a vinyl interlayer, a PPG 112 urethane interlayer, an 8 mm Herculite II chemically strengthened glass pane, a vinyl interlayer, and an 8 mm Herculite II chemically strengthened glass pane. The windshield is a plug design that utilizes aluminum retainers to secure the windshield in the fuselage opening. The anti-ice function is accomplished using PPG's Nesatron heating film to provide clear vision during inclement conditions. A polysulfide moisture seal with an embedded Z-retainer around the window perimeter protects the interlayer materials from moisture ingression.

The fractured right-hand windshield from N941FR was a part number NP165311-8 version with serial number 05052H1528. The windshield serial number indicated that the windshield was manufactured as a new unit and was completed on the 52nd day of 2005. The windshield was installed on the airplane during manufacture and it had accumulated 38,085 flight hours and 16,015 flight cycles since its installation.

The current PPG windshield for use on the Airbus 319 airplane is part number NP165331-1/-2 that entered service in April 2010. The current configuration utilizes a Herculite thermally strengthened outboard glass layer, has improved moisture seals, has a redesigned heating system with a more robust bus bar design and an optimized Nesatron conductive heating film layer, and utilizes an S-123 urethane interlayer between the outboard and center glass layers. To date, there have been no reported electrical arcing events or age related failures of this design.

Either windshield configuration is approved for installation on the Airbus 319 airplane.

The operator reported that the mean time between unit replacements for the part number NP165311-8 windshields in their fleet is about 31,863 hours. PPG reported that the average life of the part number NP165311 Airbus windshields manufactured by them is about 21,050 flight hours (7 years) based on data reported to them by operators.

An NTSB aerospace engineer oversaw the window examination and reported that the windshield exhibited a moderate network of fractures on its outer glass pane. There was evidence of repairs to the moisture seal along the entire upper and aft edges. The glass fracture pattern pointed to a primary origin centered about 4.5 inches above the lower edge of glass and 8.5 inches forward of aft edge of glass. Portions of the outboard glass pane were missing in the primary origin area. A secondary fracture origin was located about 29 inches forward of the aft edge of glass and 1 inch above the lower edge of glass. At the fracture origins there was brown, bubbled interlayer material adjacent to the fracture indicating that the windshield was powered at the time of fracture. There was evidence of an arc path in the heating film from the lower, forward corner to about 2 inches forward of the aft edge and 6 inches above the lower edge that passed through both fracture origins. There was cloudiness and cracking of the interlayer material consistent with moisture ingression adjacent to the edges of the windshield. There was no evidence of moisture ingression along sections of the window's upper edge, aft edge, and lower edge. The entire forward edge had evidence of moisture ingression. The silicone gasket was in good condition for its age. There was some discoloration of the upper and lower bus bars where visible. The foam closure plate was removed from the inner pane along the lower edge. The terminal connector at the lower, forward corner was intact with no damage noted. The sensors appeared crazed consistent with the age of the windshield. The terminal block was removed and the braid wires all appeared normal.

There was evidence of moisture ingression at the lower, forward corner of the windshield near the terminal block location. The interlayer was cracked and cloudy in the area between the location of the terminal block and the point where the arc path propagated away from the bus bar into the daylight opening of the windshield. The interlayer was also bubbled and discolored along the bus bar in this area consistent with arcing in this area.

The resistance between the pins of the terminal connector were measured before its removal and compared to the drawing specified resistance. Resistance measured between pins A and B did not meet the manufacturer's specification. The remaining pin-to-pin measurements were within specifications. The structures factual report is appended to the docket material associated with this investigation.

The operator's maintenance program outlines two separate inspections of the cockpit windshields. A detailed visual inspection of the windshields from the inside is performed at every A-check (750 flight hours, 375 flight cycles, or 121 days, whichever occurs first). The procedure outlines inspecting for cracks, scratches, chips, delamination, discoloration, interlayer microflakes, burn spots, burning, transparency, and heating film cracking. The most recent inspection of the windshield from the inside was performed on April 27, 2015, 93:52 flight hours and 43 flight cycles prior to the incident, with no findings. A detailed visual inspection of the windshields from the outside is performed every 20 months. The procedure outlines inspecting for the same items as the inside inspection with the addition of inspections for rain repellant fluid residue and a detailed inspection of the moisture seal for cracks and erosion. The most recent inspection of the windshields from the outside was performed during a scheduled C-check on April 30, 2014, 3,874:22 flight hours and 1750 flight cycles prior to the incident. The moisture seal was noted to be eroded and repaired during the C-check.

The Airbus airplane maintenance manual, customized for the operator, provides damage limits in section 56-11-11 for the windshields. The section includes limitations for cracking, scratches, chipping or flaking, delamination, discoloration, interlayer microflakes, burn spots, burning of the interlayer material, and heating film cracking.

PPG recommends inspection of the moisture seals around the periphery of the windshields every 4 months or 1,000 flight hours, whichever comes first, in their component maintenance manual. Repair of the moisture seal should occur before it has eroded enough to see the outboard edge of glass or the Z retainer.

Two of the procedures from the abnormal and emergency procedures section of the QRH were examined for this event. Procedure 80.13A Windshield/Window Arcing instructs the crew to pull the circuit breaker for the affected windshield if they see any arcing occurring or if there is a burning smell or smoke coming from the lower forward corners of the windshields near the terminal blocks.

Procedure 80.14A Windshield/Window Cracked instructs the crew to determine if the cracks are in the inner ply by touching them with a pen or fingernail. If the inner ply is not cracked, there are no limitations. If the inner ply is cracked, there are limitations for the maximum altitude and differential cabin pressure.

Subsequent to the windshield examination, the operator was asked to have the captain confirm which QRH procedures were conducted. According to the operator, the captain indicated that after 4 months since the incident, he did not remember if there was an ECAM message or if any circuit breakers had popped in reference to the QRH Window Arcing procedure 80.13A. In reference to the QHR Windshield/Window Cracked procedure 80.14A, the captain indicated that the first step to do in this procedure is to diagnose if inner ply is cracked. The flightcrew could not determine if it was the inner or outer ply that was cracked and the window appeared to possibly be melted in the bottom right corner. Since there was also smoke in the cockpit, they were unsure and assumed it was associated.

The windshield manufacturer estimates that there are currently about 800 to 1,000 of the part number NP165311 windshields in service at the time of this report.

NTSB Probable Cause

The ingression of moisture into the windshield’s laminate layer, which induced electrical arcing in the windshield heating system that subsequently cracked the outer glass pane of the windshield.