NTSB Warns Pilots: Weather Radar Can Be Misleading

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The "age indicator" on some in-cockpit weather displays can show a time stamp that's off by as much as 20 minutes, the NTSB warned in a safety alert issued on Wednesday. "Even small time differences between the age indicator and actual conditions can be important for safety of flight," the safety alert (PDF) says, "especially when considering fast-moving weather hazards, quickly developing weather scenarios, and/or fast-moving aircraft." The NEXRAD "age-indicator" on the cockpit display indicates the time the mosaic image was created, not the time of the actual weather conditions. The NEXRAD image is always older than the actual weather conditions, the NTSB said.

The NTSB said it has investigated two fatal weather-related aircraft accidents in which NEXRAD images displayed to the pilot were presented as one minute old on the age-indicator, but contained information that was up to five to eight minutes behind the real-time conditions. The mosaic images, which are available to pilots via flight information service-broadcast (FIS-B) and private satellite weather service providers, are created with radar data from multiple radar ground sites. When a mosaic image is updated, it may not contain new information from each ground site. "Let your fellow pilots know about the limitations of in-cockpit NEXRAD," the NTSB says, and always get a preflight weather briefing.