Aircraft engines are rated in stages for noise; which is the order from loudest to quietest?

• A. Stage 1 is loudest and Stage 4 is quietest
• B. Stage 1 is quietest and Stage 4 is loudest
• C. Stage 2 is loudest and Stage 3 is quietest
• D. Stage 3 is loudest and Stage 2 is quietest

Answer: (A)

Noise certification stages reflect progressively stricter limits on how loud an engine can be. Each newer stage requires more reduction in noise, so engines designed to meet later stages are quieter than those meeting earlier stages. That’s why the order from loudest to quietest follows moving from the earliest stage to the latest stage. In practice, designers achieve quieter engines through technologies that reduce propulsion and airframe noise, such as improved turbine aerodynamics, optimized fan and core flow, and advances in nacelle acoustics. Options that imply later stages are louder or that a middle stage is the loudest don’t align with how the staging system is defined.