Summary

Pursuant to a congressional request, GAO reviewed the Federal Aviation Administration's (FAA) installation of automated weather observing systems (AWOS) at commercial and general aviation airports, focusing on: (1) the performance of automated weather sensors in making weather observations in various FAA tests and demonstrations; and (2) the cost-effectiveness of installing automated systems at commercial airports that already have weather observers.

GAO found that FAA has established operational requirements for automated weather systems to ensure that they provide observations at least as accurate and complete as those presently provided by human weather observers. Both FAA and the National Weather Service, which currently provides weather reports to FAA, consider these operational requirements essential to aviation safety. However, FAA tests and demonstrations have shown that the planned automated systems do not meet operational requirements for measuring four of the nine required weather elements. Specifically, GAO found that: (1) cloud height sensors could only measure cloud ceilings up to half the height required and presently reported by weather observers; (2) visibility sensors could not measure to the required distance, and the error in their measurement increased during marginal and hazardous weather, when accurate visibility information is most important; (3) precipitation sensors could not distinguish among types of precipitation and could not detect the occurrence of precipitation 62 percent of the time; and (4) the system was not designed to detect or measure thunderstorm activity. In addition, GAO found that: (1) FAA will augment the automated systems with human observers to ensure that current weather observation requirements are met; (2) FAA incorrectly estimated both the cost of maintaining the present weather observation system and that of maintaining automated systems; and (3) it is not cost-effective for FAA to install automated weather observation systems at commercial airports.