What happened
While climbing through 20,000 feet in visual meteorological conditions, the captain's windshield shattered. The captain did not declare an emergency following the event; instead, the flight returned to the departure airport and landed uneventally. There were no injuries reported.
The investigation
The damaged windshield (PPG part number NP 139321-5, S/N 99018H7134) was removed from the aircraft for inspection. An initial examination determined that the center ply had failed. Further analysis of the component was conducted at a PPG facility in the presence of representatives from the NTSB, FAA, Bombardier, and PPG.
A report prepared by PPG identified that the fracture originated 0.20 inch from the bottom edge and 3.8 inches from the center of the forward corner. The origin of the fracture was traced to a peel chip that developed on the outboard surface in the bottom forward corner area. Specifically, the initiation point of the peel chip damage was located 0.115 inch from the inner edge of the Teflon tape and 0.325 inch from the glass edge.
Microscopic examination of the peel chip did not reveal any surface damage at the initiation point, nor were there indications of manufacturing defects. Additionally, no discrepancies were found with the anti-ice heating system or the sensing elements. While an optical distortion check showed no slope-line distortion in the critical vision area, a quantitative evaluation could not be performed due to lack of facilities. A residual visibility examination was also not possible because there is no standard prescribed method for such an evaluation.
The windshield (S/N 99018H7134) had been manufactured on January 18, 1999, and installed by Comair maintenance personnel on March 27, 1999. This window had replaced a previous unit that had shattered while the aircraft was at the gate with power off. At the time of the failure, the incident window had accumulated 4,422.8 hours and 4,526 cycles.