ERA09MA157 · Cessna 206H

The airplane was over water, operating on an instrument flight rules (IFR) flight plan at 7,000 feet, and approaching the middle of the western shore of Puerto Rico, when the pilot canceled the flight plan to “clear this weather.” The airplane subsequently turned northeast and descended to 5,500 feet. After proceeding over land for about 28 miles, and as it approached the island’s northern coast, the airplane disappeared from radar in the vicinity of a well-defined cumulus congestus cloud, containing level 5 “intense” activity, typically associated with severe turbulence. Witnesses reported seeing the airplane “spiral” and “spin straight down” from clouds before it impacted the ocean. The accident occurred 14 minutes after sunset, and the airplane did not have onboard weather radar or downloadable satellite weather, but did have a lightning detector. There were no weather advisories or pilot reports of adverse weather at the time of the accident, and no “mayday” calls from the pilot. Some smaller, less-aerodynamic items, including windshield material, were recovered on land; however, the majority of the wreckage was located 300 to 800 yards offshore. Missing items included the right horizontal stabilizer, the right elevator, the vertical stabilizer and the rudder, which could have been swept away by ocean currents. No preaccident mechanical anomalies were noted with the airplane, but weight and balance calculations indicated that it was about 300 pounds overweight at the time of the accident. The airplane’s ground speed at the end of the flight was calculated to be 189 knots; however, the in-flight airspeed during the encounter with intense weather was unknown. The airplane’s “never exceed speed” was 180 knots calibrated airspeed (KCAS), the “maximum structural cruising speed” was 147 KCAS, and the “maneuvering speed” was 123 KCAS at maximum gross weight. Observed downward bending of wing components, missing tail components, and witness reports of a “pop” or “boom” when the airplane was still at altitude indicate that portions of the tail likely separated in flight from the airplane due to overstress.

Verbatim NTSB analysis and probable cause from the NTSB dataset