Summary: GAO discussed the Federal Aviation Administration's (FAA) progress in developing its Voice Switching and Control System (VSCS), intended to provide voice communications for new controller workstations developed under the FAA Advanced Automation System. GAO noted that: (1) original estimates for VSCS prototype development increased from $67 million to $145 million; (2) total project cost estimates increased from $258 million to over $786 million; (3) prototype developers experienced unanticipated technical difficulties in meeting VSCS requirements, necessitating significant changes in proposed hardware and software; (4) technical difficulties have delayed the estimated date for VSCS implementation from 1986 to 1992; (5) prototype contractors may be striving to meet target dates at the expense of work quality; (6) VSCS development problems could delay Advanced Automation System workstation implementation; and (7) FAA does not plan to complete its testing requirements before awarding a production contract. GAO believes that FAA must complete all necessary testing before awarding the production contract to ensure that VSCS will meet its requirements.