What happened
On 22nd December 2019, a Go Airlines Airbus A320(NEO), registration VT-WJE, was performing a scheduled flight from Mumbai to Chandigarh. While climbing through flight level 210, the crew received "Engine Stall" and "High Engine Vibration" ECAM warnings for the number one engine. The vibration levels reached a maximum of 10 units on both N1 and N2 parameters, accompanied by a significant rise in Exhaust Gas Temperature (EGT).
Following established checklists, the crew reduced power on the affected engine to idle. Despite attempts to gradually increase power, the vibration levels increased again, prompting the crew to declare a return to Mumbai. The aircraft landed safely at Mumbai airport with no injuries to the 172 passengers or the crew. A subsequent visual inspection of the engine exhaust area revealed that the Low-Pressure Turbine (LPT) 3rd stage blades were broken and damaged.
The investigation
AAIB India examined the engine components and the flight history of the aircraft. The investigation focused on the physical state of the engine and the metallurgical properties of the turbine blades. Laboratory analysis conducted by NAL, Bengaluru, revealed that all 78 blades in the 3rd stage of the LPT had fractured. The study found that the fractures were brittle and instantaneous, with no evidence of progressive fatigue.
Technical evaluations confirmed that the blades were constructed from a Gamma-base Titanium Aluminide (Ti-Al) intermetallic material. While this material is used for its efficiency, it possesses low fracture toughness and is highly sensitive to impact damage. The investigation noted that this incident was part of a known series of similar failures involving this specific engine type.
Findings
- The primary cause of the incident was the failure of the LPT 3rd stage blades due to a lack of sufficient crack growth resistance and damage tolerance.
- The material used in the blades was unable to withstand impacts from debris or material liberated upstream in the engine.
- The engine was equipped with pre-modified blades that were more susceptible to such failures.
- The manufacturer had previously issued Service Bulletin 72-00-0111 to introduce a new blade design made of a more impact-resistant material.
- The airline had since complied with the necessary service bulletins to replace the affected components across its fleet.