HISTORY OF FLIGHT On September 19, 1998, at 1314 mountain daylight time, a Piper PA-20-180, N6028D, was destroyed during an emergency landing following a loss of power. The aircraft impacted in a field adjacent to a residential area in Thornton, Colorado. The commercial pilot sustained serious injuries. The flight was a banner tow operating under Title 14 CFR Part 91 and no flight plan was filed. Visual meteorological conditions prevailed. The flight originated from Aurora Air Park, Watkins, Colorado, at 1300. According to the pilot, about 14 minutes after departure while in cruise flight at 1,200 feet above ground level (agl), the engine made a loud bang, seized, and it appeared that the engine moved to the right and part of the cowling came loose. In an interview, the pilot said that following the failure, he had limited aileron control but no pitch or yaw control. He said he guided the aircraft to an open field in a residential area. Witness marks at the crash site provided evidence the aircraft struck trees beside a house located at the top of a hill above where the aircraft came to rest. After striking the trees, the aircraft impacted the ground in an inverted attitude and skidded to a stop. There was no fire and the pilot was removed from the aircraft by emergency response personnel and transported to medical facilities. PERSONNEL INFORMATION The pilot held commercial pilot certificate number 324522522 issued February 3, 1984. He held ratings in airplane single and multiengine land and an instrument rating in airplanes. According to Federal Aviation Administration (FAA) records, the pilot held a 2nd class medical certificate number EE0996624, issued March 31, 1997. There were no medical limitations. The pilot stated he had approximately 1,500 hours total flight time and approximately 250 hours in the accident aircraft make and model. AIRCRAFT INFORMATION The accident aircraft was originally manufactured as a PA-22-150 in 1956 and converted to a PA-20-180 in 1995. On December 1, 1995, the aircraft was certificated under the provisions of Federal Aviation Regulation (FAR) 21.185 as a special purpose aerial advertising aircraft. The certification was for the sole purpose of this aircraft conducting aerial advertising. According to information provided by the pilot, the airframe had a total time of 1,600 hours, 250 hours since overhaul of the engine, and 80 hours since the last inspection, which was conducted on November 1, 1997. The engine was a Lycoming O-360-A3A, serial number L-8260-36A, and the propeller was a Sensenich part number 76EM8S5-0-60, serial number 13369K. The pilot could supply no history on the propeller. WRECKAGE AND IMPACT INFORMATION Following the loss of engine power described above, the pilot was able to make approximately a 180-degree turn before the aircraft impacted trees and the ground. According to witness marks, following impact with trees at the top of a 50-foot hill, the aircraft traveled approximately 130 feet in the air, impacted the ground in an inverted attitude and skidded 52 feet. The skid track was on a base course of 205 degrees and the aircraft came to rest on a heading of 264 degrees. The ground was soft, moist, and covered with marsh grass and cattails. The engine separated from three of the four engine mounts and folded to the right side of the aircraft. One propeller blade was fractured approximately 16 inches from the hub and the outer portion was not located during the course of the investigation. The other blade of the two-blade propeller remained attached to the hub/engine and penetrated the right side of the aircraft, coming to rest between the pilot and the instrument panel. Penetration marks provided evidence the propeller was not turning at the time it penetrated the side of the aircraft and impact debris lodged against the firewall provided evidence the engine was loose from the mounts prior to impact with the trees and ground. The intact blade exhibited span wise white marks and scratches. The right wing was intact and control continuity was present. The strut remained attached and was undamaged. The left wing was crumpled accordion fashion from the tip towards the root and was compressed against the side of the fuselage. Control continuity was confirmed and the strut was folded upward. The empennage was folded scorpion fashion over the top of the aircraft. The fold was approximately 18 inches forward of the leading edge of the vertical stabilizer, which penetrated the top of the baggage compartment, located at the back end of the cabin. Control continuity to the elevators and rudder was confirmed. The cabin area remained intact and the seat belt was attached to its mounts. A shoulder harness was not installed. The main landing gear remained attached to the aircraft fuselage and was undamaged. The tail wheel remained attached and was compressed upward into the bottom of the fuselage. The banner tow was attached aft of the tail wheel and was also compressed upward. TESTS AND RESEARCH On October 6, 1998, further examination of the airframe and engine was conducted at the facilities of Beegles Aircraft Services, Greeley, Colorado. Present for the examination were an airframe and power plants mechanic from Beegles, a representative of Lycoming Engines, a representative from the FAA, and the NTSB IIC. No preaccident failure or malfunction was found during the engine examination; however, 21.5 inches of one propeller blade was missing and the remaining portion of the propeller was sent to the NTSB Materials Laboratory for further examination. Their examination provided evidence the blade had fractured due to fatigue from corrosion pitting on the convex side of the blade. For details of both the engine examination and the blade examination, refer to the attached engine and laboratory reports. Examination of the engine mounts provided evidence that three of the four mounts had pulled out of their respective firewall attachments in a forward and right direction. The fourth mount was partially fractured due to bending approximately 160 degrees at the forward edge of the mounting bolt area. ADDITIONAL INFORMATION Parties to the investigation were Lycoming Engines and the Federal Aviation Administration. The aircraft was released to the owners' representative on October 6, 1998. The propeller was returned directly to the owner.