"The Rotorcraft Master Plan advocates the establishment of additional communications, navigation, and surveillance (CNS) facilities, as well as the analysis and development of systems to satisfy the increasing demand for widespread IFR rotorcraft operations within the NAS. The objective of this study is to determine if there is an economic basis for improvement of these low altitude instrument flight rules (IFR) services within the National Airspace System (NAS) in order to better support rotorcraft IFR operations. The findings of this study will aid FAA decisionmaking in that regard. In view of prior implementation decisions on Loran-C, the emphasis in this effort is on communications, surveillance, procedural changes, and avionics. This report is one of a series of three reports that address rotorcraft low altitude IFR benefit/cost analysis. The other two are: 1) Rotorcraft Low Altitude CNS Benefit/Cost Analysis: Operations Data, DOT/FAA/DS-89/9, 2) Rotorcraft Low Altitude IFR Benefit/Cost Analysis: Methodology and Applications DOT/FAA/R D-89/1 1. This second interim report defines operational requirements and constraints for selected rotorcraft missions. A candidate list of 50 sites around the country, selected for their potential to benefit from increased low altitude IFR services, is presented. Radar and communications coverages in those areas are then identifed. CNS improvements to be provided by implementation of the NAS plan, relevant FAA policies, ATC procedures, and avionics improvements are analyzed for their potential to benefit low altitude rotorcraft IFR operations. Last, a benefit/cost methodology to determine where the most benefits would accrue from improvements in rotorcraft low altitude IFR services or changes in ATC procedures is presented."--Report documentaion page.