Pratt & Whitney will certificate the engine for the Bombardier CSeries early next year without a key feature that was part of the original design.
The PW1524G engine includes a reduction gear to slow the rotation of the inlet fan in relation to the low pressure turbine. As the fan speed slowed, P&W also added a two position variable-area nozzle (VAN) to better regulate the slower-moving airflow.
Within months of certification, however, P&W determined that the VAN system was not a necessary addition to the architecture of the PW1524G. That is because the engine also incorporates a new fan blade that performs better than expected, P&W says.
"Through the continued successful aerodynamic and mechanical development of our hybrid metallic fan blade, the PW1500G engine meets all its performance targets and certification requirements without the variable area nozzle," the company says.
The VAN may have helped to smooth the air flow exiting the engine, but it added another moving mechanical piece to an already complex architecture.
The component remains under study, however. Earlier this year, Boeing experimented for the first time with a variable area fan nozzle installed on a modified CFM56 engine on the Boeing 737-800-based ecoDemonstrator. The airframer wanted to learn more about how such a nozzle affects the engine's noise and fuel efficiency.
But neither Airbus or Boeing selected VANs as a technology to be added to the engines powering their re-engined single-aisles - the Airbus A320neo and 737 Max.