What happened
On August 21, 2014, an Air India Airbus A320, registration VT-ESI, was performing a scheduled passenger flight from Cochin to Delhi. Shortly after taking off from runway 27 at approximately 15:35 UTC, the flight crew heard a loud bang, immediately followed by an engine fire warning for the number two engine. The crew initiated ECAM emergency procedures and declared a MAY DAY call to Air Traffic Control.
During the climb, passengers also reported seeing fire from the engine. While the fire warning eventually extinguished, the crew transitioned their distress call to PAN PAN and prepared for an overweight landing. The aircraft returned to Cochin and landed safely on runway 27. There were no injuries among the 169 passengers and 4 cabin crew on board. A subsequent inspection revealed metal debris in the engine exhaust and a puncture in the C-duct cowl.
The investigation
AAIB India investigators examined the aircraft's engine components and maintenance history. The investigation focused on the physical damage to the number two engine, which included a ruptured outer and inner C-duct barrel, damaged Low Pressure Turbine blades, and a breached High Pressure Turbine (HPT) case. The inspection found that the HPT case had opened up, shearing numerous bolts and exposing the turbine area. The investigation also reviewed the maintenance records of the engine's recent overhaul.
Findings
- The investigation established that the primary cause was a failure to properly clean and inspect the No. 4 bearing seal following a lapping process during an engine overhaul.
- Lapping debris blocked the anti-weep grooves, which are designed to prevent oil from escaping the bearing compartment.
- This blockage allowed oil to migrate into the High Pressure Turbine (HPT) during sub-idle conditions.
- Upon reaching high power settings during takeoff, this accumulated oil ignited within the HPT.
- The resulting high temperatures led to a low cycle fatigue fracture of the 2nd stage air-seal, which eventually caused the HPT blades to fail and the engine casing to breach.