What happened
On November 8, 2019, an Air India Airbus A3/21-211, registration VT-PPT, was operating a scheduled flight from Bhubaneswar to Mumbai with 182 passengers and 7 crew members. While cruising at FL260, the crew heard a loud bang originating from the left engine, accompanied by a sudden left yaw and significant airframe vibration. An "ENG1 REV UNLOCK" warning appeared in the cockpit, and the left engine began to spool down.
Although no fire warning was initially triggered in the cockpit, passengers and cabin crew reported seeing fire on the left engine. The flight crew declared a "Mayday" and diverted to Raipur, the nearest suitable aerodrome. During the descent, the crew performed emergency procedures and discharged two fire extinguishing bottles after the cabin crew confirmed the presence of fire. The aircraft landed safely at Raipur at 1226 UTC. Following the landing, because the air traffic controller could still observe light indicating fire, the crew initiated an emergency evacuation. All passengers and crew successfully exited the aircraft within 50 seconds.
The investigation
The AAIB India investigation focused on the mechanical integrity of the left engine and the operational response of the crew. Investigators examined the aircraft's maintenance records, which showed the aircraft was airworthy and all mandatory service bulletins had been complied with.
Technical examinations of the left engine revealed significant internal damage. Heavy metal particles were discovered in the exhaust area, and several turbine blades were found to be heavily damaged or missing. Laboratory analysis of the Inlet Gear Box (IGB) and the No. 3 bearing module showed broken studs and significant wear. While investigators examined the No. 4 bearing and High Pressure Turbine (HPT) blades, they determined that these were secondary effects rather than the primary cause of the failure.
Findings
- The aircraft was fully compliant with all airworthiness directives and had no pending maintenance issues.
- The flight crew was properly qualified and had received adequate rest prior to the flight.
- The left engine had reached 98.98% of its life limitation (19,796 cycles against a 20,000 cycle limit).
- The failure of the IGB and No. 3 bearing module caused the engine failure and subsequent secondary damages.
- The emergency evacuation was completed successfully and safely according to standard operating procedures.