On July 14, 1999, approximately 1100 mountain daylight time, a Piper PA-18-150, N4385Z, impacted the terrain while performing aerial application at a field located about seven miles north of Opheim, Montana. The commercial pilot received fatal injuries, and the aircraft, which was owned and operated by Aero Crop Care of Las Animas, Colorado, sustained substantial damage by a post-impact fire. The 14 CFR Part 137 aerial application flight, which had been in the air for about ten minutes, was operating in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to witnesses, shortly before the accident, the pilot added fuel and application chemical to the aircraft. The pilot reportedly said that he was going to take on a partial load of both chemical and aviation fuel because he estimated the temperature to be 75-80 degrees Fahrenheit and was concerned about the reduced performance of the aircraft under the ambient conditions. Although witnesses reported that he did not fill the fuel tanks, it could not be confirmed that he took on a reduced load of chemicals. After refueling, the pilot returned to an application site that was approximately 3,000 feet above sea level (MSL). Although the field itself was relatively flat, it required executing a course reversal at one end over abruptly rising hilly terrain. After he returned to the field, witnesses saw the aircraft make a application pass in one direction, but the aircraft did not make a pass in the opposite direction. Soon thereafter witnesses noticed black smoke coming from the area where the pilot was spraying. Upon arrival at the field, these individuals found the aircraft being consumed by fire, on the aforementioned rising terrain, at a location where the pilot would be performing a course reversal just beyond the field perimeter. According to the FAA inspector who responded to the scene, the entire aircraft came to rest intact at one location. The inspector reported that there were no ground scars except for those directly underneath the position where the airframe came to rest, and no other evidence of lateral movement across the ground was found. The leading edge ribs on both wings were crushed almost directly backwards into the forward spar, and both wings had come to rest with their chord-line nearly perpendicular to the terrain (see attached photographs). The engine was still attached to the engine mount, but the mount had been deformed by the force of the engine being pushed backward into the instrument panel. Neither main gear sustained impact damage, and all four lift struts were still attached to their associated spar and longeron. Although much of the aircraft suffered post-impact fire damage, there was not evidence of direct impact damage of the wing aft of the forward spar, or of the fuselage aft of the instrument panel. A post-accident inspection of the aircraft revealed no evidence of a flight control malfunction, system anomaly, or airframe structural failure. A teardown inspection of the engine revealed no evidence of any pre-impact malfunction or anomaly that would have precluded normal operation. According to the Density Altitude Chart contained in FAA AC 61-21A (Flight Training Handbook), the density altitude at the time of the accident was approximately 4,800 feet. The FAA's Toxicology and Accident Research Laboratory conducted a forensic toxicology examination of the pilot's tissues and fluids and found no carbon monoxide, cyanide, or drugs in the blood. The test revealed 22 mg/dl of ethanol and 13 mg/dl of acetaldehyde in the blood, and 47 mg/dl of ethanol in the muscle. According to the Civil Aeromedical Institute (CAMI), ethanol concentrations of this level may be the result of postmortem ethanol production.