History of Flight
On January 30, 2008, at 2022 eastern standard time, American Airlines flight 1738, a Boeing 757-200 registered as 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 operated under Title 14 CFR Part 121 as a scheduled domestic passenger flight from San Juan, Puerto Rico, to Philadelphia, Pennsylvania, with an instrument flight rules flight plan. Night visual meteorological conditions prevailed at the time. The captain, first officer, three flight attendants, and one passenger were transported to a hospital with minor injuries. The airplane landed without incident on Runway 27R and taxied to the gate under its own power.
According to the flight crew, while at flight level 340 approximately 35 miles south of the DRIBL intersection on radial R763, they detected a burning odor and large amounts of smoke in the cockpit with no obvious source. The crew donned oxygen masks and smoke goggles, declared an emergency, and turned west toward the Florida coast. They performed the Quick Reference Handbook procedures for "Smoke/Fumes Removal." During the attempt to identify the smoke source, the first officer's windshield began to crack, and small glass shards separated and struck him. As the aircraft descended through about 10,000 feet, the windshield emitted a "very loud bang" and shattered, blocking all outside visibility.
Personnel Information
The 46-year-old captain held an airline transport pilot certificate with a B757/767 type rating and a first-class medical certificate issued on October 23, 2007. He had accumulated 182, 49, and 7 flight hours in the previous 90 days, 30 days, and 24 hours, respectively. The 41-year-old first officer also held an airline transport pilot certificate with a B757/767 type rating and a first-class medical certificate issued on August 14, 2007. He had flown 122, 46, and 7 hours in the same periods.
Aircraft Information
The Boeing 757-200 (N624AA) had undergone a scheduled A-check on January 25, 2008. The right main windshield (part number 141T4801-50, serial number 02280R7363) was installed on October 20, 2002, and had accrued 16,334 hours and 5,771 cycles. Boeing Service Bulletin 757-30-0019, which called for inspection of the lower aft terminal block for a loose connection, had not been performed on this windshield. The windshield consisted of multiple layers: an outer Herculite II glass layer, a conductive heating film, urethane and vinyl interlayers, and inner structural glass panes. Power was supplied via terminal blocks J1, J4, and J5 on the windshield edge.
Windshield Failure Examination
The damaged windshield was removed and examined under NTSB supervision at PPG Aerospace. The first officer's windshield showed two distinct fracture areas: sparse cracks in the upper third and dense small cracks in the lower two-thirds. The J4 terminal block exhibited extensive charring, and the J4 lug was missing with a charred hole in the block. The J1 terminal block had minor charring, and its braid wire was partially missing. No evidence of moisture ingression was found, but a hump seal repair was noted on the aft and upper edges. The J1 and J5 terminal connectors had fractured cap shoulders, and the J4 connector had corrosion and charring. Testing of a similar windshield from another aircraft showed that a loose screw connection could cause high temperatures at the solder joint, leading to failure. The J4 screw had orange deposits indicative of corrosion and mechanical damage consistent with tightening.
Medical and Pathological Information
The captain, first officer, three flight attendants, and one passenger were taken to local hospitals for medical evaluation and were released. None had life-threatening injuries.
Fire
The crew reported a burning smell and smoke but no visible flames. They were unable to determine the smoke source during the event. No fire extinguishers were used.
Communications
The first officer reported that communication with air traffic control was difficult due to the distance from the ATC facility and the use of oxygen masks.
Additional Information
The NTSB noted several similar events of smoke/fire at windshield heat terminal connections since 2004. In some cases, a cross-threaded screw at the J5 terminal block was the cause; in others, it was undetermined. Boeing redesigned the 757 windshield with a pin-socket connection and issued Service Bulletins 757-30-0019 and 757-30-0020 for inspections and replacements. The FAA issued a Notice of Proposed Rulemaking in April 2008 to mandate the changes.