Government and industry representatives are currently at work formulating a rule for certifying the noise levels of short takeoff and landing (STOL) aircraft. Conventional aircraft are primarily turbofan propelled and fly over well-defined landing or takeoff paths at conventional airports. In contrast to this, STOL aircraft may be propelled by propellers or rotors as well as turbofans, and will fly over varied landing and takeoff paths at new STOL ports located in or around populated areas. Therefore, it is expected that the STOL noise rule will differ from that issued late in 1969 for conventional subsonic transport aircraft. In this paper, the background information on STOL aircraft noise, STOL port site characteristics and noise evaluation units is discussed. Based on this information, the characteristics of a STOL noise rule are discussed that recognize the variety of aircraft types, the complexity of landing and takeoff paths, and the uniqueness of STOL ports which will make up the intercity air transportation system of the future.