What happened
On June 11, 2004, at 13:40, a Piper PA 42 (registration F-GXES) was conducting a cargo flight from Besançon to Valenciennes. While cruising at flight level 180, the left side window suddenly shattered, causing an explosive depressurization of the cabin.
The pilot, who was the sole occupant of the aircraft, was secured in the left seat by a three-point harness. The force of the depressurization was significant enough to pull the pilot's left arm toward the opening, causing his shoulder to strike the cockpit wall. The sudden pressure change also ejected various items from the cockpit, including flight documents, a flight plan, a headset, a jacket, sunglasses, and the left-side oxygen mask.
Following the event, the aircraft drifted 45 degrees to the left and began descending. The pilot managed to stabilize the aircraft at flight level 80. Due to damage to the left-side communication ports, the pilot had to use a second headset plugged into the right-side socket. After being instructed by air traffic control to squawk 7700, the pilot successfully landed at Valenciennes without further incident. The pilot sustained minor injuries during the event.
The investigation
The investigation focused on the structural integrity of the aircraft's windows. The left side window consisted of a 10mm thick acrylic outer pane and a 2mm thick inner pane, featuring a 15cm circular removable window for visibility in poor weather.
Investigators reviewed the maintenance history and pre-flight procedures. A Service Bulletin (SB 764) from 198t recommended visual inspections of the storm window rings for cracks or chips during pre-flight checks. The aircraft was equipped with the required instructional placard, and the pilot confirmed that the required visual inspections had been performed prior to departure. Furthermore, the most recent 100-hour inspection, conducted on May 19, 2004, included a visual examination of the window and its seals, which had revealed no defects.
Findings
- The primary cause of the incident was the explosive depressurization resulting from the failure of the left side window.
- The specific origin or mechanical cause of the window's shattering could not be determined.
- There were no malfunctions identified within the aircraft's pressurization system.
- No periodic replacement schedule was required for these specific acrylic windows.