What happened
On 4 June 2004, a Bell 412 helicopter, registration EC-GPA, operated by Helisureste, experienced the detachment of a right-hand forward emergency window while climbing to cruise altitude. The aircraft was performing a scheduled domestic passenger flight from Málaga to Ceuta with two crew members and seven passengers on board.
Approximately 15 minutes into the flight, while at roughly 1,000 feet and 125 KIAS, passengers reported a loud impact on the right side of the cabin. A passenger seated in front of the window sustained a blow to the face, resulting in a nosebleed and the loss of his eyeglasses, as fragments of the window material entered the cabin. The flight crew immediately responded by reducing the airspeed to approximately 80 KIAS. The helicopter continued the flight without further incident and landed safely in Ceuta. There were two serious and seven minor injuries reported among the occupants.
The investigation
The CIAIAC investigation focused on the maintenance history of the window assembly. Records showed that on 2 June 2004, a passenger had reported the window was slightly open. A technician subsequently repaired the window in Málaga by replacing the retainer and filler using an official repair kit. However, during a subsequent flight on 3 June, the window was found to be partially open again, leading to the installation of a new window in Ceuta using the same previously installed retainer.
The investigation examined the manufacturer's maintenance manual, which specifies that the retainer and filler must be replaced whenever the window is removed. Furthermore, the manual requires that the aircraft not be released for flight until the adhesive has cured for a minimum of 24 hours at 24 °C.
Findings
- The investigation could not determine with absolute certainty why the window and retainer detached, but identified a likely cause: the adhesive may not have achieved optimum bonding.
- It is highly probable that the helicopter was released to service without adhering to the mandatory 24-hour adhesive curing period following the maintenance performed in Málaga.
- The maintenance performed in Ceuta on 3 June involved installing a new window using the same retainer that had been recently installed, without following the specific requirement to replace the retainer and filler simultaneously with the window.
- There was no evidence of intentional manipulation of the window by passengers during the flight.