Contributor

Harry Weisberger

The FAA’s final rule on civil tiltrotor noise limits and conditions for noise compliance measurement becomes effective March 11. It amends regulations governing noise certification standards and establishes new noise limits and procedures to ensure that noise-reduction technology is incorporated in tiltrotors. 
This final rule applies to issuance of original type certificates, type certificate changes and issuance of standard airworthiness certificates. It creates noise standards applicable to all tiltrotors–currently the only civil design is the AgustaWestland AW609–and incorporates the same standards as ICAO Annex 16, Chapter 13, Attachment F. The FAA believes these noise certification standards will facilitate startup and development of a new commercial class of aircraft. It places the cost of complying with the final noise rule at $588,000 for one tiltrotor type, about the same as for a traditional helicopter design.
The only tiltrotor currently in production after more than six decades of research and development is the Bell-Boeing <a href="http://ainonline.com/aviation-news/galleries/tiltrotor-returns-farnborough-2012">V-22 Osprey</a> flown by the U.S. Marine Corps and Air Force. The V-22 can transport 24 fully equipped troops, and the AW609 can carry six to nine passengers in a corporate configuration.
The final rule adopts limits for maximum noise levels when the tiltrotor operates in its noisiest configuration–helicopter mode. In airplane mode, the tiltrotor is significantly quieter. The rule adds Appendix K to Part 36 to specify noise-evaluation measures, measurement reference points, noise limits and trade-offs. 
Maximum noise levels, at the takeoff reference point in VTOL/conversion mode, range from 109 EPNdB for tiltrotors with mtow of 176,370 pounds, decreasing with weight to 89 EPNdB. Flyover noise limits decrease from 108 EPNdB to 88 EPNdB, and from 110 EPNdB to 90 EPNdB on approach. Tiltrotor power must be stabilized at takeoff maximum starting from 1,640 feet before the flight path reference point, at 65 feet above ground.