Navaids testing risks and their mitigation

Aircrews use several methods to determine the status of navigational aids ("navaids"), including NOTAMs, broadcast messages (e.g., automatic terminal information service or ATIS), and communications with air traffic control (ATC) personnel. However, some navaids testing activities can confuse or mislead aircrews or result in radiating hazardous misleading information (HMI) which cannot be detected by monitoring systems onboard aircraft. Given the possibility of these conditions, additional precautions are necessary to ensure that aircrews do not use the misleading signals, and to minimize the number and duration of such conditions. This article identifies activities known to result in HMI and reviews anecdotal evidence of inadvertently using test signals by aircraft making normal revenue flights. It presents an analysis of the risks and describes current International Civil Aviation Organization (ICAO) and U.S. Federal Aviation Administration (FAA) activities to mitigate the risks of such testing.