Incident Details
On June 4, 2004, at approximately 11:40 UTC, a Bell 412 helicopter (registration EC-GPA) operated by Helisureste was en route from Málaga to Ceuta on a scheduled passenger flight. The helicopter was at an altitude of about 1,000 feet and an indicated airspeed of 125 knots when several passengers heard a loud impact on the right side. A passenger seated in front of the right forward window reported a blow to his face that knocked off his glasses; he covered his face and observed that the emergency window had detached, leaving plastic pieces inside the cabin. His nose was slightly bleeding. Another passenger confirmed seeing plastic fragments and no unusual behavior before the separation. The pilots reduced speed to about 80 knots indicated and continued to Ceuta without further incident. After landing, a new window and retainer were installed, and the helicopter returned to service. No further malfunctions of that window were reported through October 2004.
Window Description
The helicopter had two nearly rectangular windows made of clear acrylic on each side, which could be used as emergency exits by pushing at the lower corners. Each window weighed about 1,360 grams, measured 700 × 575 mm, and had a minimum thickness of 3.02 mm. A force of 40 to 50 pounds (20 to 28 kg) was required at the lower corners to remove it. The maintenance manual specified that the retainer and filler must be replaced each time the window was removed, and no repairs were allowed on these components. The retainer was bonded to the window frame along its contour except at the lower corners, allowing emergency opening. The manual also required an inspection every 300 flight hours for retainer adhesion and damage.
Maintenance History
On June 2, 2004, during a flight from Ceuta to Málaga, a passenger noticed that the right forward window was slightly open at its rear. After landing, a maintenance technician repaired the window by replacing the retainer and filler using an original kit (P/N 412-669-100) and reinstalling the same window. The task was recorded as completed on June 3. On the next flight to Ceuta, the window was again found slightly open. In Ceuta, the window was replaced with a new one, but the same retainer and filler were kept. The adhesive curing time for the previous retainer replacement may have been less than the required 24 hours at 24°C, though the technician stated that procedures were followed. The helicopter then operated two round trips between Ceuta and Málaga without further window issues until the separation on June 4.