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Aviation Accident

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NTSB Identification: WPR16FA067
14 CFR Public Aircraft
Accident occurred Wednesday, February 10, 2016 in Springville, CA
Probable Cause Approval Date: 01/18/2017
Aircraft: FLIGHT DESIGN GMBH CTLS, registration: N911TS
Injuries: 2 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The airplane, which was owned and operated by the local county sheriff's department, was on a low-altitude observation flight. According to GPS data recovered from the airplane, about 1 minute before the accident, the airplane was flying westbound (heading 242°) over a highway, about 500 feet above ground level (agl), and at a groundspeed of 52 knots. The GPS data and witness observations indicated that the airplane entered a left turn. According to the witnesses, the airplane's wings then dipped left and right, and the airplane descended to ground impact. The witnesses heard the engine operating in a steady tone until ground impact. A postcrash fire ensued, which destroyed the airplane.

Examination of the wreckage did not reveal evidence of any preimpact mechanical malfunctions or anomalies that would have precluded normal operation. The airplane's estimated weight at the time of the accident was about 152 lbs over the airplane's maximum gross weight. Because of the higher gross weight, the airplane's stall speed in a 30° banked turn was 3 knots higher than it would have been at the airplane's maximum gross weight. This resulted in a stall speed of about 48 knots calibrated airspeed, which was near the airplane's recorded groundspeed of 52 knots.

The sun position at the time of the accident was on a bearing of 241° and was 13° above the horizon, indicating that the pilot was looking directly into the sun before the left turn began. Another pilot who flew in the vicinity shortly after the accident reported that when flying westbound over the highway, he was looking straight into the sun, there was a lot of haze, and he could not distinguish the tops of the hills to the left of the highway from the sky. It is likely that the accident pilot was partially blinded by sun glare and did not see the hills rising above him on his left. After he entered the left turn moving away from the sun line, it is likely that the rising terrain suddenly came into view, and he increased the airplane's bank angle in order to avoid the terrain and exceeded the wing's critical angle-of-attack, which resulted in an aerodynamic stall. The altitude the airplane was operating at was too low to allow for a recovery.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
  • The pilot's failure to maintain adequate airspeed while maneuvering at low altitude in hilly terrain, which resulted in the airplane's wing exceeding its critical angle-of-attack and a subsequent aerodynamic stall. Contributing to the accident were the pilot's inability to recognize the rising terrain due to the sun glare and the pilot's operation of the airplane in excess of its gross weight.