Nexrad Weather Radar Linked to Small Plane Crash Deaths

Federal transportation experts are warning that a weather radar system used in many small planes may have caused the deaths of at least two pilots who were provided outdated weather information.

According to a safety alert (PDF) issued by the National Transportation Safety Board (NTSB), data provided by the Next Generation Radar (NEXRAD) may be older than the age actually indicated on the display, misleading pilots into believing they are viewing current weather information.

The age indicator associated with the mosaic image on the cockpit display does not show the age of the actual weather conditions as detected by the NEXRAD network, which may have played a factor in the deaths of at least two pilots, according to the NTSB warning.

Instead of the actual age of the NEXRAD data, the age indicator displays the age of the mosaic image created by the service provider. As a result, the report indicated, weather conditions depicted on the mosaic image will always be older than the age indicated on the display.

The NTSB believes the imagery could be as old as 15-20 minutes.

At least two fatal small plane crashes have been linked to the weather radar problems. In the death of one pilot in Brownsville Tennessee on March 25, 2010, the NTSB concluded the pilot’s cockpit display indicated that it had received one NEXRAD image. The image was delivered halfway through the flight. This image was indicated to be about 1 minute old. However, the information was 5 minutes old. The image indicated severe weather was about 7 miles away from the home base where the pilot was attempting to land, but the severe weather was actually just crossing over the home base at about the time the display received the NEXRAD image.

In the death of another pilot traveling near Bryon, Texas on Dec. 19, 2011, the NTSB reported the pilot had been diverting to avoid weather and had likely received several NEXRAD updates in the minutes leading up to the accident. According to the NEXRAD data the pilot likely would have received, he was flying clear of precipitation along the edge of the rain. Near the end of the flight, the pilot flew into a section of the developing rain shower. His display likely indicated that he still remained clear of the precipitation, the report concludes.

Weather radar “mosaic” imagery created from NEXRAD data is available to pilots in the cockpit via the flight information service-broadcast (FIS-B) and private satellite weather service providers. A mosaic image presents radar data from multiple radar ground sites on a single image on the cockpit display.

The slightest of differences between the age indicator and actual conditions can be important for safety of flight. The NTSB reported while this issue has been addressed in pilots’ guides, in industry literature, and on service providers’ websites, the agency has not found any documentation containing details about the potential time difference between the age indicator and actual conditions.