What happened
On 30 October 2019, an IndiGo Airbus A320-271(NEO), registration VT-ITM, was performing a scheduled flight from Kolkata to Pune with 180 passengers and four crew members on board. During the climb phase, passing approximately 9,200 feet, the flight crew heard a loud bang from the number one engine and felt the aircraft drift to the left.
Immediately following the noise, the aircraft's Engine Indicating and Crew Alerting System (ECAM) triggered both an engine stall and high vibration warning. The crew observed significant N1 and N2 vibrations, alongside Exhaust Gas Temperature (EGT) rising beyond 950°C. The crew also noted a burning smell in the cockpit, which was confirmed by the cabin crew. After reducing power on the affected engine to idle, the crew decided to divert the flight back to its point of origin. The crew declared a MAYDAY, and the aircraft landed safely at Kolkata airport without any injuries to passengers or crew.
The investigation
AAIB India conducted an investigation into the serious incident, focusing on the mechanical integrity of the engine. Post-flight inspections of the engine inlet and exhaust areas revealed extensive damage to the Low Pressure Turbine (LPT) assembly. Specifically, all blades in the LPT 3rd stage were found to be fractured.
Technical analysis performed by NAL, Bengaluru, examined the material properties of the LPT 3rd stage blades. The investigation looked into the history of similar occurrences involving the Pratt & Whitney PW1127G-JM engine and reviewed the implementation of Service Bulletin 72-00-0111, which was designed to address these specific component failures.
Findings
- The primary cause of the incident was the failure of the LPT 3rd stage blades during flight.
- Material analysis determined that the pre-modified LPT 3rd stage blades were made of a gamma-based Titanium Aluminide alloy that possessed low fracture toughness and inadequate crack growth resistance.
- The blades were unable to withstand the impact of material liberated from upstream components, leading to instantaneous brittle fractures.
- This failure resulted in the observed high engine vibrations and EGT overlimit conditions.
- The incident was part of a known series of similar events involving this engine type, which the manufacturer had previously addressed through a service bulletin introducing a more impact-resistant material.