WPR16LA023

The pilot departed on a local flight; during initial climb, the canopy partially disconnected from the airplane and the airplane vibrated violently. The pilot made a precautionary landing in a field, and the right wing impacted a fence post. Postaccident examination revealed that the mechanism that allowed the canopy to move fore and aft and retained the aft portion of the canopy during flight separated at a weld, which resulted in airflow into the cockpit. The components were not made available for metallurgical examination and the failure mode could not be determined; however, it is possible that the separation was due to repeated loading on the canopy over time. According to the pilot and a representative of the airplane type club, the canopy design was unique to the accident airplane, and was likely the only one of its kind.

On November 6, 2015, at 1530 Pacific standard time, an experimental Thorp T-18, N1488, was substantially damaged during a precautionary landing in a field near Independence State Airport, Independence, Oregon. The pilot was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The private pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan was filed. In a phone interview following the accident, the pilot stated that the airplane was climbing after takeoff when the canopy partially disconnected from the airplane and the airplane violently vibrated. The pilot landed in a cow pasture and the right wing impacted a fence post during the landing roll. He further reported that the airplane was serial number 303 and his father had built the airplane. The airplane had an early canopy design that had been modified in later designs. The canopy ran on a track. On each side of the canopy there are two fiberglass rollers and the back was secured through a track. The rear track separated and allowed airflow underneath to lift up and vibrate the canopy. The pilot believed that the separation occurred due to repeated use over time. A Federal Aviation Administration (FAA) inspector examined the airplane following the accident. The canopy mechanism allowed the canopy to move fore and aft, as well as retain the aft portion of the canopy during flight. The rear portion of the mechanism separated at a weld. The Thorp T-18 type club was contacted regarding the canopy mechanism design. The mechanism was reported as a unique design and uncommon to the fleet.