History of Flight
On June 27, 2013, at about 1020 mountain daylight time, a Cessna 172M (registration N4459R) owned and operated by IMSAR Aviation was substantially damaged when it struck powerlines and terrain during an attempted emergency landing on a road near Birdseye, Utah. The commercial pilot was seriously injured, and the required crewmember (a test engineer) received fatal injuries. The flight was a radar equipment test flight conducted under Part 91 in visual meteorological conditions; no flight plan was filed.
IMSAR used two Cessna 172 airplanes as platforms for radar system development and testing. On the accident morning, the IMSAR chief pilot flew the other company airplane, while a contract pilot operated the accident airplane. The mission plan was to fly predefined tracks and orbits at a location about 16 miles south of Spanish Fork-Springville Airport (U77) at an altitude of about 8,000 feet.
Engine start, taxi, run-up, and takeoff were uneventful. The pilot flew to the Birdseye test area via Spanish Fork Canyon and conducted straight-line track tests for about 2 hours, then began 360-degree orbits. After several orbits, the test engineer reported smelling smoke. The pilot saw smoke wafting from under the front seats and opened windows and a vent. Looking over his right shoulder, he observed an open flame about 8 inches high and 4 inches in diameter on top of test equipment behind the front seats.
The pilot decided to land as soon as possible and chose a nearby road. He maneuvered for a northbound right-hand downwind leg, broadcast a mayday on 121.5 MHz, and received a response from an overflying airliner to whom he briefly relayed the situation. He then focused on landing, configuring the airplane for a southbound landing on the road. About 30 feet above the road, he visually detected a powerline suspended above the road and pulled up to overfly it. The airplane struck that wire, then other powerlines and terrain. There was no post-impact fire. Passers-by aided the pilot and contacted emergency services.
Personnel Information
The pilot held commercial pilot and flight instructor certificates with single-engine land ratings. He had about 2,528 total flight hours, including about 2,088 hours in single-engine airplanes and 20 hours in the accident make and model. His most recent flight in the accident airplane was about 1 month prior. He was a part-time contract pilot who began flying for IMSAR in early February 2013. IMSAR equipment test flights always included a pilot and an engineer/observer. The pilot was responsible for flying and executing test ground tracks; the engineer performed equipment mounting and hookup and operated the equipment.
The test engineer was an IMSAR engineering employee, not a pilot. He had flown in the accident airplane three times previously (on June 14 and June 18) with the IMSAR chief pilot. He did not incur thermal injuries; his death was impact-related.
Aircraft Information
The airplane, a 1974 Cessna 172M (serial number 17263201), was equipped with a Lycoming O-320 engine. It was purchased by IMSAR Aviation in February 2013 and modified for radar equipment testing. The airplane was registered in the restricted category. At the time of the accident, it had about 2,111 total hours; its most recent annual inspection was on June 2, 2013. The airplane flew 11.2 hours on five flights before the accident. The certification basis required flame-resistant cabin furnishings but did not include smoke, fume, or particulate criteria. No fire extinguisher was on board, nor was one required by FAA or IMSAR.
Wreckage and Impact Information
The accident site was about 15 miles south of U77. The pilot attempted an emergency landing to the south on US Highway 89 at an elevation of about 5,520 feet. On-scene evidence showed the airplane struck two sets of powerlines: one east-west transverse set with two lines, and one north-south parallel set with four lines. The first struck wire was the highest transverse wire about 28 feet above the road; the second transverse wire at 23 feet was not struck. The airplane then struck at least two wires in the parallel set, the highest at about 35 feet. The nose landing gear first struck the transverse cable; the right wing and main landing gear subsequently struck the parallel cables. The airplane came to rest inverted about 270 feet south of the transverse strike, with no components separated. Control cable continuity was established throughout the airplane.
Examination revealed that a supplemental electrical system installed to power radar equipment had overheated and begun to burn. Thermal damage was confined to the operator-installed electrical system and airplane furnishings. The supplemental power supply system was designed by IMSAR and included a battery, inverter, power distribution box, and other components. The power distribution box was stacked on a battery box and secured with a cargo strap. Wires were pressed between the battery box cover and distribution box, with no provisions for positioning or separation. The installation had no vibration envelope requirements or wire abrasion resistance specifications. The radar technician who fabricated the system was not an FAA-certified mechanic. No guidance for physical installation was provided by the operator.
Meteorological Information
The 0955 automated weather observation at an airport 20 miles north included variable wind at 3 knots, visibility 15 miles, clear skies, temperature 26°C, dew point 9°C, altimeter 30.25 inHg. At the accident time, the sun's azimuth was about 98° from true north, elevation 47° above the horizon.
Additional Information
IMSAR designed and manufactured synthetic aperture radar systems primarily for DoD airborne platforms. The supplemental power supply was an internal product flown only on company aircraft, subject to IMSAR design standards. The system components, including a battery, inverter, and distribution box, were not permanently affixed and were loose-laid or stacked. The wiring was not protected against chafing in the high-vibration environment of a piston-engine airplane.
The powerlines were not marked with conspicuity devices, nor were they required to be.