On August 22, 2010, about 1150 Pacific daylight time, a Grumman AA-5A airplane, N26118, sustained substantial damage during a forced landing, about 1 mile north of the Lake County Airport, Lakeview, Oregon (LKV). The private pilot and passenger were not injured. The airplane was operated by the pilot as a personal cross-country flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91, when the accident occurred. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at Lakeview, and was en route to Burns, Oregon. The pilot reported that during the preflight and preflight run-up he did not detect any anomalies with the airplane’s engine. Shortly after takeoff, at approximately 150 feet above ground level (agl), the engine revolutions per minute (rpm) dropped from 2,500 to 1,500 rpm. The pilot immediately checked fuel quantities, and attempted to lean the engine. Despite the pilot’s efforts, the problem persisted, and the pilot initiated an off-airport landing to an open field about 1 mile north of LKV. The pilot stated that during the landing roll, the airplane’s left wing struck a fence post and the empennage collided with tall sage brush, both of which resulted in substantial damage to the airplane. Postaccident examination of the airplane by a certificated airframe and powerplant (A&P) mechanic revealed that the airplane’s left wing and empennage sustained substantial damage. When an engine compression test was conducted, no compression was found in the number three cylinder. Further examination revealed that the exhaust valve was stuck in the full open position. The examination revealed no further anomalies with the cylinder assembly or engine.