On July 5, 2011, about 1050 Pacific daylight time, a Grumman AA-5, N1334R, collided with a tree and then terrain near Yacoit, Washington. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The commercial pilot and one passenger sustained serious injuries; the airplane sustained substantial damage from impact forces. The personal cross-country flight departed Grove Field, Camas, Washington, about 1040, with a planned destination of Grant County Regional/Ogilvie Field, John Day, Oregon. Visual meteorological conditions prevailed, and a visual flight rules (VFR) plan had been filed.The pilot reported that he departed straight out from runway 25, and opened his flight plan. He contacted Portland Approach Control for VFR flight following. Approach Control instructed him to remain clear of the class C airspace until they had positive radar identification. The pilot reversed his course, and the airplane was back abeam Grove Field. He remained on an easterly heading, and climbed to 2,400 feet. He observed rising terrain to the east. He decided to head back to the west, and maintained a reduced power setting and 100 miles per hour (mph) airspeed. Portland Approach contacted the pilot and stated that they had radar contact, and queried when he could accept a clearance to continue on course. He replied that he could proceed on course immediately, and indicated that his position was about 4 miles from the Gymme intersection, which was the first waypoint on his planned route of flight. He requested to cruise at 9,500 feet mean sea level (msl). He added full power, and began a climbing left turn to proceed on course. The pilot stated that he did not lose adequate terrain clearance at any time during the course reversal. The airplane was at full power climbing about 400-500 feet per minute. About 3,000 feet msl, he felt a small bump, and noted that the airspeed dropped to 80 mph. He verified that the throttle was in full, and then noticed that the airspeed dropped to 60 mph, which he said was 2 mph above the clean stall speed. While maintaining 60 mph with full power, the airplane began descending. At this point, the pilot noticed that a large fir tree was in the airplane's path; he stated that the airplane had about 1,000 feet of clearance above the tree's elevation prior to the bump. He started a gentle 4-degree bank turn to avoid the tree. The airplane descended until the right wing collided at midspan with a smaller unseen tree. The airplane came to rest in a gravel pit. Both the pilot and passenger sustained broken legs and lacerations; the pilot sustained broken fingers on his right hand as well, which he attributed to his maintaining the full throttle position until touchdown. The pilot stated that his preflight forecast was for calm conditions to 6,000 feet, and he did not encounter any turbulence during the flight. The Federal Aviation Administration (FAA) accident coordinator interviewed a bystander who came to the aid of the airplane's occupants. The bystander arrived about 5 minutes after the crash; he observed one person with a shattered ankle standing by the left side of the airplane, and one person still in the right seat. He noted that he saw a small fuel leak from under the left wing, and there was a fuel odor. Two FAA inspectors examined the airplane on scene. They observed a 5-gallon bucket under the left wing with about 1/2 inch of fuel in it. They opened the fuel caps on each wing tank, but could not determine if any or how much fuel was in the tanks. The FAA accident coordinator interviewed the pilot. The pilot indicated that he was maintaining a low altitude to avoid the controlled airspace above him. The pilot initiated a left turn to avoid rising terrain ahead, and could not estimate the altitude above ground level (agl). The pilot did not think that winds were a factor, but that the airplane might have been too low at the intuition of the turn. The FAA accident coordinator interviewed the passenger. The passenger stated that he was looking around enjoying the flight and the scenery as they were heading up a valley. He did recall looking at the engine gauges as this time, and the engine rpm was in the green operating range. The engine sounded good up until the end. As he looked back to the front of the airplane, he and the pilot almost simultaneously stated that they were not going to make it. The pilot indicated that they would be all right if they could get between two trees. The airplane hit one of the trees, and then the ground. The passenger was not sure what direction the airplane was headed or if it was turning. He felt that all changes to the airplane's flight path were controlled at all times, and did not think that there were air pockets, updrafts, or downdrafts that affected the airplane's flight path.