Relying on NEXRAD data proves fatal for pilot

This October 2010 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

Aircraft: Cessna 210. Injuries: 1 Fatal. Location: Aiken, S.C. Aircraft damage: Substantial.

What reportedly happened: There was no record of the pilot, who did not have an instrument rating, obtaining a weather briefing or filing a flight plan. The pilot was on a VFR cross-country flight when an air traffic controller advised him that a broken line of weather with moderate-to-heavy precipitation existed and extended almost to the destination airport.

During the ensuing conversation, the pilot advised the controller that he was underneath the weather and that he had weather radar. The pilot then entered the weather in the vicinity of his destination airport.

Radar imagery, witness statements, and measurements from local surface stations indicated that areas of light, moderate, and possibly heavy precipitation existed and that the airplane was most likely in instrument meteorological conditions in its final two minutes of flight. According to radar data, the pilot’s altitude control became erratic after entering the weather, and the airplane entered an ever-tightening right turn, consistent with the pilot experiencing spatial disorientation. The airplane completed about two and a half 360° turns of progressively smaller diameter before radar contact was lost, and the airplane hit terrain.

Examination of the wreckage revealed no evidence of any pre-impact malfunction or failure of the airplane or engine, and it did not reveal any evidence that on-board weather radar was installed.

During the wreckage examination, the remains of a portable global positioning system receiver were discovered. The receiver was not certificated for use under instrument flight rules and was intended by the manufacturer to be used as an aid for VFR navigation. It was capable of displaying weather data and images from the NEXt-generation RADar (NEXRAD) ground radar network, but, unlike on-board weather radar, transmitted NEXRAD data is not real-time. The manufacturer cautioned that the lapsed time between collection, processing, and dissemination of NEXRAD images can be significant, and, therefore, they should only be used for long-range planning purposes and not for short-range weather avoidance.

Furthermore, according to the FAA, NEXRAD data or any radar data should not be used to penetrate hazardous weather. Rather, it should be used in an early-warning capacity of pre-departure and en route evaluation. As discussed in the Safety Alert issued by the NTSB on in-cockpit NEXRAD, because NEXRAD images present radar data from multiple ground sites as a single mosaic image, the age indicated on the NEXRAD image does not show the age of the actual weather conditions but rather represents the time when the mosaic image was created. The actual weather conditions could be up to 15 to 20 minutes older than the age indicated on the image. Both the FAA and the NTSB advise that advanced avionics weather data systems should not be used as a substitute for a pre-flight weather briefing.

Probable cause: The pilot’s inadequate weather planning and improper decision to continue a VFR flight into IMC, which resulted in a loss of control due to spatial disorientation. Contributing to the accident was the pilot’s improper use of in-cockpit next generation radar imagery for short-range weather avoidance.

For more information: NTSB Identification: ERA11FA038

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