EASA Expands eVTOL Noise Standards, Limits

The European Union Aviation Safety Agency (EASA) has published noise standards for electric vertical-takeoff-and-landing (eVTOL) aircraft, releasing the final version of its specification for multicopter aircraft and inviting public consultation on its draft specification for aircraft with tilting rotors.

The Environmental Protection Technical Specifications (EPTS) for eVTOLs are based on existing international noise standards for conventional aircraft, adjusted to accommodate the characteristics of what EASA calls VTOL-capable aircraft (VCA).

The documents establish procedures for measuring noise on approach, takeoff and in overflight, plus a hover noise assessment to help evaluate the impact of operations close to vertiports. The documents also set the certification limits for noise at each of the measurement points.

Noise is required to be measured using reference procedures for takeoff, overflight, approach and hover. The procedures are essentially the same for both classes of eVTOL, with the exception that requirements for aircraft with tilting rotors also take into consideration nacelle angle.

For eVTOLs with tilting rotors, EASA proposes measuring takeoff and approach noise with the nacelle angle corresponding to the best rate of climb speed. Overflight noise measurement is divided into VTOL/conversion and airplane modes. For VTOL/conversion mode, nacelles are maintained at the lowest angle certified for zero airspeed. For airplane mode, nacelle angle is near 0 deg.

While most eVTOL developers say their aircraft are significantly quieter than helicopters, EASA has not adjusted the noise limits downward for VCA. Maximum noise limits are set for aircraft with a maximum takeoff weight of 80,000 kg (176,000 lb.) and reduce logarithmically to a weight of 788 kg, then stay constant. Typical weights for eVTOL air taxis now under development are 3,175 kg or less.

For both eVTOL classes, noise limits are 86-106 EPNdB for takeoff, 84-104 EPNdB for overflight and 89-109 EPNdB for approach. There is no maximum noise level for hover.

For comparison, a typical light twin-turbine helicopter such as the Airbus EC135 has a takeoff noise level of 88.6 EPNdB versus a limit of 94.5, 84 EPNdB for overflight (vs. 93.5) and 92.7 EPNdB for approach (vs. 95.5). This is louder than for a single-turbine fixed-wing aircraft such as the Daher TBM 900, which has takeoff noise level of 79.6 EPNdB versus a limit of 85.

In NASA tests, the flyover noise generated by Joby Aviation’s 2,200-kg-class S4 tiltprop was measured as 45.2dBA at 500 m (1,640 ft.) altitude. A direct comparison is not possible, as dBA measures loudness while ENPdB measures annoyance by adjusting the sound level to account for human response, but the results indicate eVTOLs are significantly quieter.