What happened
On 20 July 2016, a Saab-Scania SF340B, registration G-LGNC, was performing a commercial passenger flight departing from Glasgow Airport. Shortly after passing 9,000 feet, the commander observed that the upper section of the left engine 'Figure of 8' cowling was flapping due to airflow.
In response, the pilot halted the climb at 10,000 feet and performed two orbits to allow cabin crew to secure the cabin. During these maneuvers, the loose cowling began to vibrate with significant intensity. The commander reduced the aircraft speed to the minimum clean speed, which mitigated the vibration, and subsequently returned the aircraft to Glasgow. The flight landed safely with no injuries to the 3 crew members or 13 passengers on board.
The investigation
Post-flight inspections revealed that the left hand upper nacelle fairing had sustained damage to its leading edge. Additionally, the trailing edges of all four propeller blades on the left engine showed signs of damage caused by contact with the cowling.
An investigation by the operator identified that an engineering staff member had been distracted during a maintenance task the previous day, resulting in the cowling not being properly secured before the aircraft was dispatched. Furthermore, it was discovered that some fasteners used were of an incorrect length; these protruded even when properly secured, which made it harder to identify unsecured components during both engineering and flight crew inspections.
Findings
- The primary cause of the incident was an unsecured left engine cowling following maintenance.
- A maintenance technician was distracted during the previous day's work, leading to the failure to secure the component.
- The unsecured latches were not identified by engineering personnel during pre-flight checks, nor by the flight crew during their external walk-around.
- The use of incorrect-length fasteners created a visual difficulty in detecting improperly secured parts.