History of Flight
On September 16, 2019, at approximately 1925 UTC, a Swiss International Air Lines (SWISS) Airbus Canada A220-300, registration HB-JCA, equipped with two Pratt & Whitney PW1524G geared turbofan engines, experienced a failure of the No. 1 (left) engine during climb, just before reaching cruise altitude of FL350. The flight was over the Côte-d'Or region of northeastern France. The flight crew performed quick reference handbook procedures, declared an emergency, and returned to Geneva Airport (GVA), where they made an uneventful single-engine landing. The regularly scheduled passenger flight was operating from GVA to London Heathrow Airport (LHR). No passenger or crew injuries were reported.
The investigation was conducted under ICAO Annex 13, with the National Transportation Safety Board (NTSB) accepting delegation from the French Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile (BEA). The Transportation Safety Board of Canada (TSB) and the Swiss Transportation Safety Investigation Board (STSB-AV) also participated.
Damage to the Airplane
There was no damage to the airplane structure.
Test and Research
The incident engine, serial number P736195, was examined at the P&W Columbus Engine Center. The low-pressure compressor (LPC) forward case had missing material from the 3 to 11 o'clock positions. The LPC mid case had a 360-degree circumferential crack and was missing material from the 7 to 10 o'clock positions. LPC stages 2 and 3 showed secondary impact damage. A borescope inspection of the engine core revealed impact damage and material loss through all eight high-pressure compressor stages and both high-pressure turbine stage 1 blades and stage 2 vanes were missing material.
Metallurgical analysis of the recovered LPC stage 1 integrally bladed rotor (IBR) fragment identified a high-cycle fatigue crack originating at the runout of an airfoil leading edge root radius, approximately 0.0033 inch beneath the surface. No material or processing anomalies were found near the crack origin, and no cyclic markers or arrest lines were observed.
Testing and analysis determined that at specific engine operating conditions, an acoustic tone generated by the 2.5 bleed valve located aft of LPC stage 3 rotor excited coupled LPC stage 3 and stage 1 IBR rotor modes. This acoustic coincidence, combined with blade flutter response, created stress levels exceeding material limits, leading to crack formation and IBR fracture. Factors that contributed to the acoustic coincidence included an electronic engine control (EEC) software revision that altered the LPC variable inlet guide vane (IGV) schedule and tighter LPC IBR blade tip clearance due to low time on the engine.
Between July 25, 2019, and February 12, 2020, four PW1500G series LPC stage 1 IBR separations occurred on multiple operators; this incident was the second. The engine parameters and damage patterns were consistent in all events.
Corrective Actions
Corrective actions were released by Pratt & Whitney, the Federal Aviation Administration (FAA), Airbus Canada, and Transport Canada. These included recurrent borescope inspections of the LPC stage 1 IBR, which identified two additional crack findings in the fleet. An engine low rotor speed (N1) restriction above FL290 was implemented. EEC software update V2.11.9 reverted the LPC vane schedule to the original, and update V2.11.10 automated a 95.2% N1 speed limit above FL290. Pratt & Whitney began installation of a redesigned 2.5 bleed valve in the fourth quarter of 2021 to provide adequate frequency separation.