Airbus has resumed flying the PW1100G-powered A320neo flight test aircraft in Toulouse, France after a three-month grounding.
The A320neo is still scheduled to be delivered to launch customer Qatar Airways by the end of the year despite the flight test delay.
The grounding was traced to a fault in a 25.4cm (10in)-diameter snap ring buried in the heart of the engine with the combustor module.
P&W has acknowledged the company inadvertently skipped a step when the snap ring was manufactured.
The part needs to be pre-stressed so it does not slightly change shape when exposed to the intense heat around the combustor module, but the pre-stressing process failed to occur for a batch of snap rings.
The mistake caused Airbus to ground the A320neo fleet while P&W disassembled the engine, manufactured a new snap ring and installed it.