Narrative:

I work as an air traffic controller at roanoke regional airport in roanoke; virginia. This facility provides air traffic control services to approximately five airports as well as over-flight traffic. The facility's airspace is largely located in an area of mountainous terrain. The service is provided 24 hours a day. During the overnight hours our facility staffing is reduced to two full performance controllers. This requires that the controllers switch from our primary airport radar (ASR8) to cenrap. FAA's aeronautical information manual describes cenrap as; 'an alternative to the ASR facilities should an ASR fail or malfunction'. Switching to cenrap disables several functions that are critical in providing safety to aircraft operating at night in mountainous terrain. These disabled functions include; altitude encoding; MSAW (minimum safe altitude warning); and ca (collision alerts). Losing the ability to monitor an aircraft's altitude directly from transponders severely inhibits our ability to monitor an aircraft's altitude during critical phases of flight. We have no means; other than verbally from the pilot; to observe altitude deviations. In the same way; MSAW is disabled removing another means to alert controllers of inappropriate altitude. The suppression of collision alerts is another obvious safety compromise. The use of cenrap is not an acceptable replacement for an existing; functional radar system.

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Original NASA ASRS Text

Title: ROA controller voiced concern regarding the facility's use of CENRAP operations during mid shift operations listing a number of RADAR limitations utilizing the alternative RADAR equipment.

Narrative: I work as an Air Traffic Controller at Roanoke Regional Airport in Roanoke; Virginia. This facility provides Air Traffic Control services to approximately five airports as well as over-flight traffic. The facility's airspace is largely located in an area of mountainous terrain. The service is provided 24 hours a day. During the overnight hours our facility staffing is reduced to two full performance controllers. This requires that the controllers switch from our primary airport RADAR (ASR8) to CENRAP. FAA's Aeronautical Information Manual describes CENRAP as; 'an alternative to the ASR facilities should an ASR fail or malfunction'. Switching to CENRAP disables several functions that are critical in providing safety to aircraft operating at night in mountainous terrain. These disabled functions include; altitude encoding; MSAW (minimum safe altitude warning); and CA (collision alerts). Losing the ability to monitor an aircraft's altitude directly from transponders severely inhibits our ability to monitor an aircraft's altitude during critical phases of flight. We have no means; other than verbally from the pilot; to observe altitude deviations. In the same way; MSAW is disabled removing another means to alert controllers of inappropriate altitude. The suppression of collision alerts is another obvious safety compromise. The use of CENRAP is not an acceptable replacement for an existing; functional radar system.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.