On May 5, 1993, about 0702 hours Pacific daylight time, a Grumman 164A- 600, N5249, crashed during a forced landing near Biggs, California. The airplane was being operated as a visual flight rules (VFR) aerial application flight under Title 14 CFR Part 137 when the accident occurred. The airplane, operated by Williams Ag Service, was destroyed by impact and post impact fire. The certificated commercial pilot, the sole occupant, received fatal injuries. Visual meteorological conditions prevailed. The flight originated from a private airstrip located about 1 mile north of Biggs about 0700 hours. The operator reported that the airplane departed the airstrip with about 1700 pounds of rice seed that was to be applied on a nearby field. After departure, witnesses observed the airplane about 50 feet above the ground while enroute to the field. Witnesses reported hearing the engine "pop" and produce sputtering sounds. The airplane then descended toward an open field that was adjacent to water covered fields and bordered by an irrigation ditch. The airplane struck the inside slope of a raised irrigation levee bank, about 4 feet below the edge. The airplane nosed over and a post crash fire erupted around the engine area. Airworthiness and Operations Inspectors from the Federal Aviation Administration, Sacramento Flight Standards District Office, examined the airplane at the accident site. They reported that the number 2 cylinder separated from the engine at the top of the cylinder barrel. The number 9 cylinder exhibited cracking and partial separation at the top of the cylinder barrel that was similar to the number 2 cylinder. The number 9 cylinder also received impact damage to the top of the cylinder head. Additionally, the number 3 cylinder exhibited a crack that extended from the front spark plug hole to the top of the cylinder head, and down toward the cylinder barrel/head joint. Fire damage to the airplane was limited to the engine area and did not propagate to the cockpit. The airplane's load of rice seed was not jettisoned. The pilot held a commercial pilot certificate with airplane single engine land and multiengine land ratings. The most recent second class medical certificate was issued to the pilot on February 10, 1993, and contained the limitation that correcting lenses be worn while exercising the privileges of his airman certificate. Safety Board investigators reviewed the pilot's FAA medical records back to 1988. Since April 14, 1988, the pilot's applications for medical certificate indicated that no medications were being taken by the pilot. According to the pilot/operator report submitted by the operator, the pilot's total aeronautical experience consists of about 13,850 hours. In the preceding 90 and 30 days prior to the accident, the report lists a total of 75 and 60 hours respectively flown. The airplane had accumulated a total time in service of 6,587.7 flight hours. Examination of the maintenance records revealed that the most recent annual inspection of the engine and airframe was accomplished on April 15, 1993, 51.7 flight hours before the accident. The engine had accrued a total time in service of 7,761 hours of operation and had accrued 924.6 hours since a major overhaul was accomplished on June 22, 1990. On June 4, 1991, after accruing 249 hours since the overhaul, the engine was removed from the airplane due to metal contamination and was sent to a repair facility. The repairs included replacement of pistons, rings, and magneto drives. The engine was reinstalled in the airplane on July 25, 1991, and operated for 675 hours before the accident. Due to the damage that the number 2 cylinder received, the total time accrued on the cylinder is unknown. The closest official weather observation station is Chico, California, which is located 19 nautical miles northwest of the accident site. At 0652 hours, a surface observation was reporting in part: Sky condition and ceiling, 25,000 scattered; visibility 40 miles; wind, 340 degrees at 4 knots; altimeter, 29.97 inHg. The pilot was wearing a helmet on the accident flight. Witnesses reported that upon arrival at the accident scene, the pilot was still restrained by the seatbelt; however, the pilot's helmet was lying next to the pilot and not in position on his head. A post mortem examination of the pilot was conducted by the Butte County Coroner's Office on May 6, 1993. According to the report, the cause of death was attributed to multiple trauma including a fracture to the thoracic spine. No pre-existing conditions were noted during the post mortem examination which would have adversely affected the pilot's abilities to pilot the airplane. A toxicological examination was conducted by the FAA Civil Aeromedical Institute (CAMI) on October 14, 1993, and revealed the presence of Metoprolol in the blood and urine. According to toxicologists at CAMI, Metoprolol is prescribed for hypertension or angina. No medical records or prescriptions for Metoprolol were located for the pilot.