What happened
On 21 February 2008, an Expo Aviation Fokker F27 (registration 4R-MRA) was performing a scheduled domestic passenger flight from Colombo Airport, Ratmalana, to Palali Airport, Jaffna. Shortly after takeoff, while the aircraft was climbing through approximately 200 feet, the crew received an engine fire warning accompanied by a cockpit alarm.
The First Officer immediately initiated the necessary actions and silenced the warnings. Following the instructions of the Pilot-in-Command, the crew executed the emergency fire drill according to the established checklists. The pilot subsequently decided to return the aircraft to the departure airport. The flight landed safely at Ratmalana with the left engine feathered. There were no injuries to the 38 passengers or the 4 crew members on board.
The investigation
An investigation was launched by the Civil Aviation Authority of Sri Lanka following the notification of the incident. Inspectors examined the aircraft upon its return to the ground. The inspection revealed damage to the engine cowling, the engine mount assembly, and the combustion chamber No. 1. Specifically, the coupling flange of the Accessory Gear Box (AGB) drive shaft was found to be bent and discolored, and the shaft's universal joint cover had sheared.
The investigation focused on the Accessory Gear Box Drive Shaft of the No. 1 engine. It was discovered that the shaft had detached from the bearings of the universal joint assembly at the engine end. This caused the rotating shaft to strike the combustion chamber No. 1, resulting in impact damage to the outer air casing flange and the expansion chamber. While the fire warning system was triggered, investigators found no evidence of a fuel leak; instead, the warning was caused by hot cooling air escaping from the damaged combustion chamber.
Findings
- The AGB Drive Shaft had been recently installed, having completed only 4.58 flight hours since its overhaul.
- The overhaul process for the drive shaft was found to be substandard and deviated significantly from the required maintenance manual.
- The overhaul failed to replace essential components, including oil sealing rings and bearing needle rollers.
- The failure of the drive shaft at the universal joint caused it to strike the combustion chamber, leading to the release of hot air that triggered the fire warning.