ENG08IA011

the arcing of the windshield heat system at the upper, aft (J1) and upper, forward (J4) terminal locations on the first officer's windshield, which caused the inner pane of glass to fracture.

During cruise flight the crew experienced smoke in the cockpit, none of it coming from an obvious place, followed by the fracture of the inner pane of the first officer's windshield. They declared an emergency and diverted the airplane to a local airport where an uneventful landing was made. Examination of the widow revealed evidence of arcing at the upper, aft (J1) and upper, forward (J4) windshield heat terminal locations and inner pane fracture initiation beneath the upper, forward (J4) terminal block. The initiation point for the arcing at both terminal locations could not be identified due to the damage sustained.

HISTORY OF FLIGHT On January 30, 2008, at 2022 eastern standard time, American Airlines flight 1738, a Boeing 757-200, N624AA, declared an emergency due to smoke in the cockpit and diverted to Palm Beach International Airport (KPBI), West Palm Beach, Florida. The flight was being piloted by an airline transport pilot certificated captain and airline transport pilot certificated first officer. The airplane landed without incident at KPBI. Night visual meteorological conditions prevailed at the time of the incident. The scheduled domestic passenger flight was being conducted under the provisions of Title 14 CFR Part 121, and an instrument flight rules flight plan had been filed. The captain, first officer, three of the six flight attendants, and one passenger were transported to the hospital with minor injuries. The flight departed San Juan, Puerto Rico, at 1851 atlantic standard time and was enroute to Philadelphia, Pennsylvania. According to the flight crew, the airplane was at flight level (FL) 340, approximately 35 miles south of the DRIBL intersection on radial R763, when they noticed a burning odor and large amounts of smoke in the cockpit, none of it coming from an obvious place. The crew donned their oxygen masks and smoke goggles, declared an emergency, and turned the airplane westbound towards the Florida coast. They accomplished the Quick Reference Handbook procedures for "Smoke/Fumes Removal". While trying to determine the source of the smoke, the first officer noticed that his windshield began to crack and small shards of glass began to separate and strike him. They began a descent and about 10,000 feet the first officer's windshield made a "very loud bang" and shattered, blocking all outside visibility. The airplane landed on Runway 27R and taxied to the gate under its own power. PERSONNEL INFORMATION Captain The 46-year-old captain held an airline transport pilot certificate with a type rating for B757/767 airplanes and a first class medical certificate. His most recent medical certificate was issued on October 23, 2007, and his most recent flight review was performed on November 14, 2007. He had accrued 182, 49, and 7 flight hours in the last 90 days, 30 days, and 24 hours, respectively. First Officer The 41-year-old first officer held an airline transport pilot certificate with a type rating for B757/767 airplanes and a first class medical certificate. His most recent medical certificate was issued on August 14, 2007, and his most recent flight review was performed on October 5, 2007. He had accrued 122, 46, and 7 flight hours in the last 90 days, 30 days, and 24 hours, respectively. AIRCRAFT INFORMATION The Boeing 757-200 airplane, N624AA, was last inspected during a scheduled A-check on January 25, 2008. According to American Airlines maintenance records, the windshield was installed on the airplane on October 20, 2002. Boeing Service Bulletin 757-30-0019 calling for inspection of the lower, aft terminal block for a loose connection had not been performed on the windshield at the time of the incident. The windshield was reported to have accrued 16,334 hours and 5,771 cycles since installation. The windshield is manufactured of the following materials, from the outboard surface to the inboard surface; a 0.120" thick Herculite II chemically strengthened glass layer, a PPG Nesatron conductive heating film layer for deice capability, a 0.030" PPG 112 urethane interlayer, a 0.140" vinyl layer, a 0.020 PPG 112 urethane interlayer, a 0.380" Herculite II chemically strengthened glass layer, a 0.080" vinyl layer, and a 0.312" Herculite II chemically strengthened glass layer. The center and inner panes of glass and the vinyl and urethane layers are secured in a Phenolic edge and the windshield is secured in the fuselage with an aluminum retainer on top of the Phenolic edge. The anti-ice function is accomplished using PPG's Nesatraon heating film on the inner surface of the outboard glass ply. A polysulfide moisture (hump) seal around the window perimeter protects the interlayer materials from moisture ingression. A silicon seal on the inner surface of the Phenolic edge provides sealing between the windshield and the fuselage mounting structure. The middle and inboard panes of glass are considered structural panes and certification testing is performed to demonstrate that the windshield is capable of carrying a differential pressure load of 19.2 psi with one structural pane fractured. Boeing also requires that the windshield must withstand a differential pressure load of 11.8 psi for at least 15 minutes with all panes of glass fractured. Power to the windshield heat system is supplied through three terminal blocks on the edge of the windshield; J1 at the upper, aft corner, J4 at the upper forward corner, and J5 at the lower aft corner. Two terminal blocks along the upper edge (J2 and J3) provide sensing functions for the system. At each of the upper terminal blocks a braid wire is soldered to one side of the terminal lug and is routed around the glass plies to a bus bar along the upper edge of the window heating film. At the lower terminal block two braid wires are soldered to the side of the terminal lug and routed around the glass plies to each end of the bus bar along the lower edge of the heating film. The terminal blocks are potted to the edge of the window with a polysufide sealant after soldering. The window heat controller supplies the power to the system. The Boeing electrical requirements for the system are a maximum voltage of 186 Volts root mean square (RMS) from the controller and a resistance between the upper and lower bus bars of 9.12 to 11.15 Ohms. At the end of each of the power wires from the airplane a terminal connector is installed. The connector is attached to the block with a screw and washer. METEOROLOGICAL INFORMATION The company reported the following weather at KPBI at 2053: wind from 150 degrees at 5 knots, visibility 10 miles, sky clear, temperature 22 degrees Celsius, dew point 17 degrees Celsius, and an altimeter of 30.12 inches of Mercury. COMMUNICATIONS The first officer reported that communication with air traffic control was difficult due to the distance between the airplane to the air traffic control facility and utilizing the oxygen masks. MEDICAL AND PATHOLOGICAL INFORMATION The captain, first officer, three flight attendants, and one passenger were transported to local hospitals for medical evaluation and released. FIRE The crew reported a burning smell and smoke in the cockpit but did not observe any visible flames. They were not able to determine the source of the smoke during the event. None of the fire extinguishers were expended during the incident. TEST AND RESEARCH The damaged right main windshield (P/N 141T4801-50, S/N 02280R7363) and attached wiring harness were removed from the airplane by American Airlines maintenance personnel and shipped to the manufacturer, PPG Aerospace in Huntsville, Alabama. The window was examined under National Transportation Safety Board (Safety Board) supervision on February 21, 2008. The windshield serial number indicates that the windshield was a remanufactured unit and was completed on the 280th day of 2002. The first officer's windshield exhibited two distinct areas of fracture on the inner pane of glass. The upper 1/3 of the windshield exhibited long sparse cracks that curved from the upper, forward corner of the windshield towards the upper, aft corner. The lower 2/3 exhibited a dense network of small cracks that obscured the visibility through the windshield. The lower, aft (J5), terminal block was intact with no obvious damage. The upper, forward (J3) and aft (J2) terminal blocks were intact with no obvious damage. There was no evidence of moisture ingression on the windshield. There was evidence of a hump seal repair to the aft and upper edges. The upper bus bar exhibited some discoloration.