What happened
On January 3, 2019, an IndiGo Airbus A320-271 NEO, registration VT-ITW, was operating a scheduled flight from Chennai to Kolkata. While the aircraft was climbing through Flight Level 210, the crew heard a loud bang, followed immediately by an engine stall alert on the Engine Centralized Aircraft Monitor (ECAM).
Following the stall, the crew observed high vibrations in the second engine (N1 at 10 and N2 at 8) and an Exhaust Gas Temperature (EGT) exceeding 9/00°C. In response to these abnormal parameters, the flight crew executed the required checklists and decided to divert the aircraft back to its departure point. The aircraft landed safely at Chennai International Airport with no injuries to the 172 passengers or 4 cabin crew members on board.
The investigation
An investigation by AAIB India focused on the mechanical condition of the engine following the incident. A post-flight inspection of the engine inlet and exhaust areas revealed extensive damage. Specifically, all blades of the Low Pressure Turbine (LPT) 3rd stage were found to be fractured from the tips.
Further borescope inspections revealed several other issues, including a bent rotor blade in the High-Pressure Compressor (HPC) Stage 8, damage to the combustion chamber, and erosion and burn-through on the High-Pressure Turbine (HPT) Stage 1 blades. The investigation also involved failure analysis by the National Aerospace Laboratories (NAL) in Bengaluru, which examined similar fractured blades from other engines.
Findings
- The primary cause of the incident was the failure of the LPT 3rd stage blades.
- The blades, constructed from a Gamma-based Titanium Aluminide (TiAl) intermetallic material, were found to be inherently brittle with low fracture toughness.
- Metallurgical analysis confirmed that the blades fractured instantaneously in a brittle manner when subjected to impact, rather than through progressive fatigue.
- The engine was equipped with pre-modification blades that lacked sufficient damage tolerance to withstand material liberated from upstream components.
- The aircraft and crew were fully compliant with all regulatory requirements, including valid airworthiness certificates and appropriate pilot licensing.