On June 29, 2001, about 1350 Alaska daylight time, a wheel-equipped Piper PA-18-150 airplane, N6881B, sustained substantial damage during a forced landing at a private airstrip located about 2 miles north of Palmer, Alaska. The airplane was being operated as a visual flight rules (VFR) personal flight under Title 14, CFR Part 91, when the accident occurred. The certificated private pilot, and the one passenger aboard, sustained serious injuries. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at the accident airstrip about 1349. A witness to the accident reported to the Alaska State Troopers that just after the accident airplane departed from the 800-feet long airstrip, the engine began to run rough and lose power. The witness said that it appeared that the pilot was trying to turn the airplane around in an attempt to return to the airstrip, and subsequently struck the surface of an open field next to the airstrip. The airplane sustained substantial damage to the wings, fuselage, and empennage. A Federal Aviation Administration (FAA) airworthiness inspector from the Anchorage Flight Standards District Office, traveled to the accident scene on June 29, and examined the airplane. He reported that the airplane came to rest upright with the left wing still attached to the fuselage, but the right wing was torn from the airplane during the impact. The FAA inspector noted that both wing fuel tanks remained intact and were not breached. He added that the left fuel tank appeared to be about 2/3 full, and the right tank was empty. The fuel selector valve was selected to the right fuel tank. The FAA inspector interviewed a neighbor that lives close to the accident airstrip who responded to the accident site, just after the accident. The neighbor stated that in conjunction with responding fire rescue personnel and Alaska State Troopers, he was one of first to reach the accident site. He reported that during the rescue attempts of the pilot and passenger, Fire Department personnel asked him to move the right wing away from the fuselage. In the process of moving the severed wing, he noted that the right wing fuel tank was empty, with no visible signs of postaccident spillage. While at the accident site an Alaska State Trooper removed the right wing fuel cap, and verified that the right wing fuel tank was empty. The pilot did not to submit a Pilot/Operator report (NTSB form 6120.1/2).