What happened
On July 15, 2019, an IndiGo Airbus A320-271(NEO), registration VT-ITU, was performing a scheduled flight from Goa to Ahmedabad. While the aircraft was climbing through 26,000 feet, the crew heard a loud bang, followed immediately by an Engine #1 stall alert on the Engine-Indicating and Crew-Alerting System (ECAM).
The flight crew responded by following the Quick Reference Handbook (QRH) procedures, reducing the thrust lever for the affected engine to idle. During the event, the crew observed high N1 vibrations of 10 and N2 vibrations of 6.7, alongside Exhaust Gas Temperature (EGT) levels rising beyond 900°C. Due to these abnormal parameters, the crew shut down the engine in flight. The aircraft subsequently performed an air turn-back and landed safely at Goa. There were no injuries to the 178 passengers or the four cabin crew members on board.
The investigation
An investigation by the AAIB examined the engine components following the incident. A post-flight visual inspection of the engine inlet and exhaust areas revealed significant damage to the Low Pressure Turbine (LPT) 3rd stage blades. Further borescope inspections identified several other issues, including scratches on the High-Pressure Compressor (HPC) stage 8 blades, damage to the High-Pressure Turbine (HPT) stage 1 blades, and damage to LPT stage 2 blades.
Technical analysis conducted by NAL, Bengaluru, focused on the material properties of the LPT 3rd stage blades. The study determined that the blades were constructed from a gamma-based Titanium Aluminide (TiAl) alloy, which is inherently brittle and possesses low fracture toughness. The investigation confirmed that the blades lacked sufficient crack growth resistance and damage tolerance to withstand impacts from material liberated upstream in the engine.
Findings
- The primary cause of the incident was the failure of the LPT 3rd stage blades due to their inability to withstand impact damage.
- The material used in the pre-modified blades was prone to instantaneous fracture once a crack initiated, as it lacked adequate damage tolerance.
- This incident was part of a known series of similar events involving the PW1127G-JM engine type.
- The aircraft and crew were fully compliant with all airworthiness directives and operational requirements at the time of the event.