What happened
On 26 October 2019, an IndiGo Airbus A320-271(NEO), registration VT-IZT, was operating a scheduled flight from Delhi to Goa. While the aircraft was climbing through approximately 28,200 feet, the crew heard a loud bang, followed immediately by an engine stall alert and high vibration warnings on the Engine 2 ECAM.
As the flight progressed, the crew observed Exhaust Gas Temperature (EGT) levels rising beyond limits. Following established procedures, the pilots decided to divert back to Delhi. During the descent, the crew performed a commanded in-flight shutdown of the second engine. The aircraft subsequently landed safely at Delhi on a single engine with no injuries to the 162 passengers or 4 cabin crew members on board.
The investigation
AAIB India examined the engine following the incident. A visual inspection of the engine inlet and exhaust areas revealed that all blades in the Low Pressure Turbine (LPT) 3rd stage had fractured. Further technical examination showed damage to the LPT 2nd stage vanes and disk, as well as contact damage on the LPT drive shaft.
Metallurgical analysis conducted by NAL, Bengaluru, determined that the LPT 3rd stage blades were constructed from a gamma-based Titanium Aluminide (TiAl) alloy. The study found that this specific material possessed low fracture toughness and inadequate crack growth resistance. The investigation established that the blades were prone to instantaneous fracture upon impact from any upstream material liberation.
Findings
- The primary cause of the incident was the failure of the LPT 3rd stage blades due to a material lack of damage tolerance.
- The pre-modified blades were highly sensitive to impact, meaning any small piece of debris could trigger a catastrophic fracture.
- This incident was part of a known series of similar occurrences involving the same engine type.
- The engine was equipped with the original, un-modified LPT 3rd stage blades, which lacked the improved resistance found in newer versions.