14 CFR § 91.815 - Agricultural and fire fighting airplanes: Noise operating limitations.
(a) This section applies to propeller-driven, small airplanes having standard airworthiness certificates that are designed for “agricultural aircraft operations” (as defined in § 137.3 of this chapter, as effective on January 1, 1966) or for dispensing fire fighting materials.
(b) If the Airplane Flight Manual, or other approved manual material information, markings, or placards for the airplane indicate that the airplane has not been shown to comply with the noise limits under part 36 of this chapter, no person may operate that airplane, except -
(1) To the extent necessary to accomplish the work activity directly associated with the purpose for which it is designed;
(3) To conduct “nondispensing aerial work operations” in accordance with the requirements under § 137.29(c) of this chapter.