SEA98FA083

The purpose of the flight was to demonstrate the airplane's performance envelope and flight characteristics to an individual who had recently invested in the company, that produces the kits for building this experimental aircraft. For the first five minutes of the flight, the Mustang flew in formation with an aircraft being flown by a company official, and then the Mustang demonstration pilot proceeded to an area south of Marsing, Idaho. The aircraft was observed performing a series of maneuvers in that area under a ceiling that was estimated at 2,000 to 2,500 feet AGL. Recorded electronic engine performance data indicated that the aircraft's throttle was retarded to idle about a minute and forty-five seconds prior to impact. Witnesses said that after they heard the power reduced, the aircraft climbed for awhile and then began to slow. As the aircraft's speed became 'very slow' its nose dropped and it lost a few hundred feet of altitude. After leveling off and slowing again, the aircraft's nose dropped a second time. Soon thereafter the aircraft rolled to the left and impacted the ground from an altitude that was estimated to be between 75 feet and '...two and one-half times the height of the nearby power line towers.' The recorded engine data showed that about five seconds before impact, the aircraft's throttle was pushed forward to about 72%, and the engine accelerated to almost 4,100 rpm. About one second before impact the throttle was retarded to idle.

History of flight

On May 30, 1998, approximately 1245 mountain daylight time, an experimental Papa 51 Thunder Mustang, N151TM, impacted the terrain about six miles south of Marsing, Idaho. The commercial pilot and his passenger, who held a private pilot certificate, received fatal injuries, and the aircraft, which was owned and operated by Papa 51 Ltd., of Nampa, Idaho, was destroyed. The 14 CFR Part 91 personal pleasure flight, which was being conducted to demonstrate the performance capabilities of the aircraft to the private pilot, departed Nampa Municipal Airport, Nampa, Idaho, about 20 minutes prior to the accident. No flight plan had been filed, and according to witnesses, the aircraft was being operated in visual meteorological conditions. There was no ELT transmission as the ELT had been removed for repair.

According to a company representative, the private pilot rated passenger had invested in Papa 51 Ltd., about four months prior to the flight, and this was the first opportunity to demonstrate the Thunder Mustang's performance and flight characteristics to this individual. About 1220, the company demonstration pilot and the investor departed Nampa Airport. Approximately the same time, a Papa 51 company official, piloting a Glassair III, took off from Nampa and joined up with the Mustang in formation flight west of Nampa Airport. After maneuvering together for about 5 minutes, the company official in the Glassair told the two pilots in the Mustang that he and his passenger were going to return to the airport. As the Glassair pilot turned east toward Nampa, the Mustang pilot turned to proceed to the west. Soon after the two aircraft separated, the demonstration pilot in the Mustang advised the company official flying the Glassair that the alternator light on the Mustang had just illuminated, but that they would complete the demonstration flight before returning to Nampa. According to the company official in the Glassair, since the Mustang had been flown before using battery power only after a loose wire had rendered the alternator inoperative, there was no further discussion of the illumination of the light. Except for the failed alternator indication, there had been no indication from the demonstration pilot that there was anything abnormal or unusual about the flight. In addition, neither of the individuals in the Glassair had noticed anything that would indicate that there was something wrong with either the Mustang or its pilot.

Soon after the two aircraft separated, a number of individuals noticed the Mustang performing a series of maneuvers in an area about five miles south of Marsing, Idaho. A number of these witnesses reported that when the aircraft was first seen, it was approaching the area from the direction of Marsing, and was traveling in relatively level flight at a high rate of speed. Once in the area near where the accident took place, the aircraft was seen climbing, descending, turning at varying degrees of bank angle, and maintaining level flight for brief periods of time. The witnesses reported that during this series of maneuvers, there were times when the engine sounded like it was running smoothly at a high power setting, times when the engine sounded as if it were "popping", "sputtering" or "backfiring" at a reduced power setting, and times when it could not be heard at all. During this period, which most witnesses indicated lasted between five and ten minutes, no smoke or fluids were seen trailing the aircraft, and no one reported seeing any structural components separate from the airframe.

Almost all of the witnesses reported that a short period of time before the impact, they heard "backfiring" and "popping" sounds, as they had during some of the previous maneuvers. This was followed by another period during which no engine sounds could be heard, except for an occasional backfiring sound heard by some of the witnesses. Individuals who heard this period of zero or reduced engine sound, gave estimates of a duration from 30 seconds to over a minute. According to the few witnesses who were still watching the Mustang during this last period of reduced engine sound, the aircraft appeared to climb for a short period of time after the reduction of engine noise, and then began descending while heading to the south toward slightly rising terrain. A number of witnesses lost sight of the aircraft as it proceeded to the south, but two witnesses reported watching the Mustang until it impacted the ground. According to one of these witnesses, during the final portion of its flight, the aircraft's southerly course paralleled Highway 95, about one mile west of the highway. This individual reported that he watched the aircraft as it passed about 1.5 miles east of his residence and proceeded to the south at high speed. He said that it flew over a ridge that runs between his home and Highway 95, and that the aircraft appeared to be between 1,000 and 2,000 feet above the ground. He also commented that when he initially heard the engine it was running fine, but as it continued to the south, it sounded to him like it "backfired" and then was silent. He reported that the aircraft began to slow as it proceeded south in level flight, and then its nose dropped sharply, and the aircraft appeared to lose a few hundred feet. The aircraft then returned to level flight and continued to the south. The witness said that during its return to level flight, the engine might have accelerated a little bit, but he was not certain. As it once again continued to the south, its speed over the ground appeared to slow significantly, and according to this witness became "very slow." When asked for an estimate of its speed, the witness stated that it looked to him as if the aircraft was going 35 to 40 miles per hour. As the aircraft approached the location where it ultimately struck the ground, the nose was once again seen to drop, followed by another loss of altitude. One of the two witnesses said that there was no engine sound after this second nose drop, and that during the altitude loss, the aircraft rolled left and descended into the ground. The other witness said that it sounded as if the pilot "got back on the gas" for a short period of time after the nose dropped, followed immediately by the initiation of a left turn. This witness further stated that while the aircraft was in the turn, it sounded to him like the engine "stopped altogether," and then the aircraft "...gently rolled into the ground." One of the witnesses reported that after the second nose drop, the aircraft was about 75 feet above the ground, and the other described it as about 2 to 2 1/2 times the height of the nearby power line towers. Both witnesses said that immediately upon contacting the ground, the aircraft was engulfed in a ball of fire.

Meteorological information

At 1215, about five minutes prior to the time the two aircraft departed Nampa Airport, the Aviation Routine Weather Report (METAR) taken at Caldwell, Idaho, which is located about 13 miles north-northeast of the accident site, reported calm winds, 10 statute miles visibility, scattered clouds at 3,100 feet and 3,700 feet, broken clouds at 5,000 feet, a temperature of 13 degrees Celsius, and a dewpoint of 6 degrees Celsius. At 1254, about 10 minutes after the accident, the METAR from the same location indicated calm winds, 10 miles visibility, scattered clouds at 3,800 feet and 4,700 feet, broken clouds at 6,000 feet, and a temperature/dewpoint of 13 and 7 degrees Celsius. The METAR taken about ten minutes after the accident at Boise Air Terminal, located about 30 miles east of the accident site, reported winds variable at 4 knots, 10 miles visibility, few clouds at 3,200 feet, scattered clouds at 4,000 feet, broken clouds at 6,500 feet, and a temperature/dew point of 13 and 6 degrees. According to the pilot of the Glassair, there was a broken to overcast ceiling of about 2,000 to 2,500 feet (AGL) in th