What happened
On 19 August 2019, an IndiGo Airbus A320-271(NEO), registration VT-IVO, was preparing for a scheduled flight from Guwahati to Kolkata. During the takeoff roll at Guwahati Airport, the flight crew increased thrust to takeoff power while the aircraft was stabilizing at 50% N1. Immediately following the power increase, a loud bang was heard from the left side of the aircraft, accompanied by intense vibrations and a tendency for the plane to veer to the left.
The flight crew promptly initiated a rejected takeoff at a ground speed of approximately 30 to 35 knots. The aircraft's Electronic Centralized Aircraft Monitor (ECAM) indicated an Engine #1 stall and high vibration. After bringing the engine thrust lever to idle, the crew obtained clearance from Air Traffic Control and taxied the aircraft back to the gate. There were no injuries to the 174 passengers or 4 cabin crew on board, and no fire was reported.
The investigation
An investigation by the AAIB examined the engine's condition following the event. A visual inspection of the Engine #1 inlet and exhaust areas revealed that the Low Pressure Turbine (LPT) 3rd stage blades and stator vanes were damaged. A subsequent borescope inspection of the High-Pressure Turbine also identified minor tip damage on a 1st stage blade. Additionally, an oil chip was detected in Engine #1 upon engine shutdown.
Technical analysis conducted by NAL, Bengaluru, focused on the material properties of the LPT 3rd stage blades. The study determined that the pre-modification blades were composed of a gamma-based Titanium Aluminide (TiAl) alloy. This specific material was found to be brittle, possessing low fracture toughness and inadequate crack growth resistance. The investigation established that the blades were unable to withstand impacts from material liberated upstream, causing cracks to propagate instantaneously and lead to fracture.
Findings
- The incident was part of a known series of similar events involving LPT 3rd stage blade failures.
- The LPT 3rd stage blade material lacked sufficient damage tolerance and crack growth resistance to withstand upstream impacts.
- The engine manufacturer, Pratt & Whitney, had previously identified this as a known issue and issued Service Bulletin 72-00-0111 to introduce a more impact-resistant blade material.
- All required airworthiness documentation and pilot qualifications were in order at the time of the incident.