Birdseye, UT, USA
N4459R
CESSNA 172
***This report was modified on August 18, 2015. Please see the docket for this accident to view the original report.*** A company that designed and manufactured airborne radar units, primarily for military applications, was using the accident airplane (as well as one other airplane) for some of the airborne development and testing of the externally mounted radar equipment. The pilot was in the left seat and a test engineer, who was not a pilot, was in the right seat. The airplane was equipped with a supplemental electrical power supply system that the company had designed and manufactured to provide electrical power for the radar systems and support equipment on the test flights. Most of the supplemental power supply system was located in the combined baggage area and the area vacated by the removal of the rear seats. In its installed position, the supplemental power supply system was not intended or able to be reached by the pilot or engineer during flight. About 2 hours into the radar test flight, the test engineer smelled smoke in the airplane. The pilot attempted to locate the source of the smoke and observed an open flame on the supplemental power supply. Because the fire was out of the pilot's or engineer's reach and the airplane was not equipped with a fire extinguisher, the pilot decided to land as soon as possible. During the attempted emergency landing on a road, the airplane struck power lines suspended above the road and then impacted the ground. Detailed examination of airplane and power system components revealed that the fire involved several wires that connected directly to the power system battery and that the fire had spread to the airplane floor carpet. The supplemental electrical power supply system components included, in part, an automobile-type 12-volt direct current battery, which was encased in a covered, plastic box, and a company-designed and -manufactured hard-plastic power distribution box. The power distribution box was stacked on top of the battery box, and they were secured in place by a ratcheting cargo strap system. In that configuration, two 12- to 14-gauge plastic-insulated wires, one red and one black, were situated and pressed between the top cover of the battery box and the bottom of the power distribution box, and then routed into the distribution box via a single grommeted hole in the bottom of that box. The installation had no provisions for separating or protecting the two wires, and the evidence was consistent with the wires abutting or crossing one another while pressed between the two boxes. The high-vibration environment of the test airplane caused relative motion between the two boxes and/or the boxes and the wires. That relative motion, combined with the pressure exerted by the boxes on the wires, abraded the insulation of those wires, which then allowed their conductors to contact one another. Because the black wire was connected directly to the negative battery terminal and the red wire was electrically connected to the positive battery terminal, contact of those conductors yielded a direct electrical short. The wires were rated to carry a maximum current of about 45 amperes, and the battery-rated output was 750 amperes. The short circuit resulted in a significant overcurrent in the wires, which caused excessive heating, additional insulation failure, smoke, and fire. Although the pilot did not recall all of the details of the event, the evidence indicated that the fire produced a significant amount of soot and heavy particulate matter, and possibly other physiological irritants. The wire installation was not in accordance with Federal Aviation Administration (FAA) maintenance guidance, which advised that wire insulation be protected against chafing or abrasion because damage can result in a short circuit. The appearance of the supplemental electrical power supply, particularly its intercomponent wiring, was consistent with that of test-bench equipment, designed to be operated in a stationary environment with minimal or no vibration. No guidance or other documentation regarding the physical installation of the system components in the airplane or the security and protection of the associated wiring was located. A company technician, who was not an FAA-certified aircraft mechanic, reported that he accomplished the original installation of the supplemental power supply a few weeks before the accident; the power supply had accumulated about 13 hours of operation since its installation. The investigation was unable to determine if, how many times, or by whom, the power supply or its components might have been adjusted, moved, removed, and/or reinstalled. It could also not be determined whether the company-contracted aircraft mechanic had provided any installation guidance or whether he had examined, changed, or otherwise contacted or disturbed the original installation, because that mechanic did not respond to requests for information. The installation and arrangement of the affected wires were not in compliance with acceptable practices for aircraft, and the installation presented a serious hazard to flight safety due to the high potential for insulation abrasion and failure, with the resultant unintended electrical path(s).
HISTORY OF FLIGHTOn June 27, 2013, about 1020 mountain daylight time, a Cessna 172M, N4459R, was substantially damaged when it struck powerlines and terrain during an attempted emergency landing on a road near Birdseye, Utah. The airplane was owned and operated by IMSAR Aviation, a wholly owned subsidiary of IMSAR, of Springville, Utah. The commercial pilot was seriously injured, and the required crewmember received fatal injuries. The radar equipment test flight was operated under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight. According to representatives of IMSAR, the airplane was one of two Cessna 172 airplanes used as platforms for the development and testing of airborne radar systems. The airplanes were based at Spanish Fork-Springville airport (U77), Springville, Utah. IMSAR employed one full time pilot, and occasionally utilized the services of contract pilots. On the morning of the accident, the IMSAR pilot was operating the other company airplane, and a contract pilot was operating the accident airplane. The mission plan was to fly predetermined tracks and/or orbits at a location about 16 miles south of U77, at an altitude of about 8,000 feet, for several hours. The engine start, taxi, run-up, and takeoff were uneventful. The pilot flew toward the assigned test location of Birdseye via the Spanish Fork Canyon. The IMSAR-required test altitude for this particular flight was 2,500 feet above ground level. The airplane arrived on station over Birdseye and conducted the straight-line track portion of the test program, which took about 2 hours. The pilot then began flying some 360-degree orbit (circling) tracks, remaining near the Birdseye area. After flying several orbits, the test engineer told the pilot that he smelled smoke. The pilot discontinued the orbiting, and began looking for the smoke and its source. He noticed smoke wafting from under the front seats toward the front of the aircraft, and opened both windows and one vent to evacuate the smoke. He then looked over his right shoulder, towards the rear of the airplane, and observed an open flame about 8 inches high and 4 inches in diameter. The flame was situated on top of one of the test equipment components that were located behind the front seats. The pilot made the decision to land as soon as possible, and after visually scanning the region below, he decided that landing on the road was the best option. The pilot maneuvered the airplane for a northbound, right-hand downwind leg, and simultaneously broadcast a "mayday" communication on the emergency frequency of 121.5 MHz. He received a response almost immediately from an overflying airliner, and briefly advised the airliner of the situation, providing airplane registration number, location, nature of the problem, and his intentions. The pilot then ceased communicating on the radio, and focused on the landing. He configured the airplane for landing, and set up to land to the south on the road. Just before the planned touchdown, when the airplane was about 30 feet above the road, the pilot visually detected a powerline that was suspended above the road and in his path, and pulled up in an attempt to overfly it. The airplane struck that wire, and then struck other powerlines and terrain. There was no post impact fire. Passers-by came to the aid of the pilot, and contacted emergency services to notify them of the accident. PERSONNEL INFORMATIONPilot Federal Aviation Administration (FAA) records indicated that the pilot held commercial pilot and flight instructor certificates with single-engine land ratings. According to information provided by the pilot, he had approximately 2,528 total hours of flight experience, which included approximately 2,088 hours in single-engine airplanes, and 20 hours in the accident airplane make and model. He had most recently flown the accident airplane about 1 month prior. His most recent flight review was completed in November 2012, and his most recent FAA first-class medical certificate was issued in May 2013. According to the pilot, he was a part-time contract pilot who began flying for IMSAR in early February 2013. At that time, as part of his orientation, he was instructed on what IMSAR-related equipment was already installed in the airplane, what equipment would typically be brought to the airplane from the IMSAR office by test personnel, and "generally how to mount and connect that equipment." His most recent flights for IMSAR were on May 31, 2013, and one of those flights was about a 1-hour familiarization flight in the accident airplane; that familiarization flight was the pilot's first flight in that particular airplane. That flight was "completely normal" and "uneventful," and the pilot "found nothing about the aircraft or the flight to be unusual, particularly challenging or bothersome." The pilot reported that IMSAR equipment test flights always included 2 persons; 1 pilot and 1 engineer/observer. The pilot was responsible for flying the airplane to the test area, and executing the designated flight test ground tracks, which were depicted on the panel-mounted guidance equipment. The pilot stated that the engineer/observer generally had the responsibility to either perform or assist with the equipment mounting and hookup, and that specific operations of the equipment were the responsibility of the engineer/observer. The pilot incurred serious impact injuries, but no fire- or thermal-related injuries. Test Engineer The test engineer was an engineering employee of IMSAR. He was not a pilot. According to documentation provided by IMSAR, he had flown as the test engineer in the accident airplane twice on June 14, and once on June 18. The durations of those flights were 4.0, 2.5, and 2.0 hours, respectively. The pilot for all three of those flights was the IMSAR chief pilot. The test engineer did not incur any thermal injuries; his death was impact-related. AIRCRAFT INFORMATIONFAA information indicated that the airplane was manufactured in 1974 as Cessna serial number 17263201, and was equipped with a Lycoming O-320 series engine. The airplane was purchased by IMSAR Aviation in February 2013, and modified for mounting and testing of the radar equipment. IMSAR Aviation utilized the services of an independent FAA mechanic with an inspection authorization rating for some of the modifications. The airplane was registered to IMSAR in the restricted category. At the time of the accident the airplane had accumulated approximately 2,111 hours total time in service. Its most recent annual inspection was completed on June 2, 2013, and it had accumulated about 13 flight hours since that inspection. Review of the airplane flight logs indicated that the airplane was not operated during the period from February 23, 2013, to May 30, 2013, inclusive. The airplane flew one flight of 1.0 hours on May 31. It then flew two flights on June 14, and one each on June 17 and June 18. The next flight was the accident flight. The respective durations of those five pre-accident flights were 1.0, 4.0, 2.5, 1.7, and 2.0 hours, for a total time of 11.2 hours. The certification basis for the airplane required that the cabin furnishings, including the floor carpet, be "flame resistant." The regulations and certification criteria defined a "flame resistant" material as material "which will not support combustion to the point of propagating, beyond safe limits, a flame after the removal of the ignition source." The certification basis did not include smoke, fume, or particulate criteria. There was no fire extinguishing equipment on board, nor was a fire extinguisher FAA- or IMSAR- required equipment for the flight. FAA requirements for general aviation aircraft certificated subsequent to the certification of the accident airplane mandated equipping those aircraft with fire extinguishers. METEOROLOGICAL INFORMATIONThe 0955 automated weather observation at an airport located about 20 miles north of the accident site included variable wind at 3 knots, visibility 15 miles, clear skies, temperature 26 degrees C, dew point 9 degrees C, and an altimeter setting of 30.25 inches of mercury. According to astronomical data from the National Oceanic and Atmospheric Administration, at the accident location about the time of the accident, the sun's azimuth was about 98 degrees from true north, and its elevation was about 47 degrees above the horizon. AIRPORT INFORMATIONFAA information indicated that the airplane was manufactured in 1974 as Cessna serial number 17263201, and was equipped with a Lycoming O-320 series engine. The airplane was purchased by IMSAR Aviation in February 2013, and modified for mounting and testing of the radar equipment. IMSAR Aviation utilized the services of an independent FAA mechanic with an inspection authorization rating for some of the modifications. The airplane was registered to IMSAR in the restricted category. At the time of the accident the airplane had accumulated approximately 2,111 hours total time in service. Its most recent annual inspection was completed on June 2, 2013, and it had accumulated about 13 flight hours since that inspection. Review of the airplane flight logs indicated that the airplane was not operated during the period from February 23, 2013, to May 30, 2013, inclusive. The airplane flew one flight of 1.0 hours on May 31. It then flew two flights on June 14, and one each on June 17 and June 18. The next flight was the accident flight. The respective durations of those five pre-accident flights were 1.0, 4.0, 2.5, 1.7, and 2.0 hours, for a total time of 11.2 hours. The certification basis for the airplane required that the cabin furnishings, including the floor carpet, be "flame resistant." The regulations and certification criteria defined a "flame resistant" material as material "which will not support combustion to the point of propagating, beyond safe limits, a flame after the removal of the ignition source." The certification basis did not include smoke, fume, or particulate criteria. There was no fire extinguishing equipment on board, nor was a fire extinguisher FAA- or IMSAR- required equipment for the flight. FAA requirements for general aviation aircraft certificated subsequent to the certification of the accident airplane mandated equipping those aircraft with fire extinguishers. WRECKAGE AND IMPACT INFORMATIONThe accident site was located about 15 miles south of U77. The airplane was examined on-site by FAA and IMSAR personnel on the day of the accident, and then by FAA, NTSB, and Cessna Aircraft Company personnel the day after the accident. The pilot was attempting an emergency landing to the south on US Highway 89, a two-lane north-south asphalt road. The road is situated in a north-south valley about 50 miles south of Salt Lake City. The approximate impact location was at an elevation of about 5,520 feet above mean sea level. The airplane came to rest on terrain about 15 feet lower than, and about 25 feet west of, the road. On-scene evidence was consistent with the airplane striking two separate sets of powerlines. The first set was oriented east-west, transversely across the road, and consisted of two lines. The second set was oriented north-south, parallel to the road, and consisted of four lines. The two powerline sets shared a common weathered-wood support pole located about 40 feet west of the roadway centerline. That pole was one in a series of poles that paralleled the road, and which supported the four-powerline group. The poles in that group were spaced about 350 feet apart. The eastern end of the transverse powerline set was supported by another weathered-wood pole. That pole was situated in a field, and was located about 250 feet east of the road. The airplane first struck and broke the highest powerline in the transverse (east-west) set. That fractured powerline was situated about 28 feet above the road. It had an overall diameter of 0.316 inches, and the nominal rated tensile strength of the cable was 2,850 pounds. A second similar cable in the transverse set, which was situated about 23 feet above the road, was not struck, and remained intact. The airplane then struck at least two separate cables that were in the four-line set that paralleled the roadway on its west side. The uppermost cable was situated about 35 feet above the road, The cable was significantly damaged but not completely fractured; all but one strand of that cable were "bunched" at the south end of an approximately 18-foot section, consistent with them being fractured and then compressed along the single intact strand by the airplane. The overall cable diameter was 0.398 inches, and the nominal rated tensile strength of the cable was 4,380 pounds. A second similar cable, situated about 4 feet closer to the road than, and 3 feet below, the top cable, was completely fractured. Two other cables in that group were not fractured but displayed electrical arcing burns in the vicinity of the bunching. None of the powerlines were marked or highlighted with any devices (such as balls) to increase their visual conspicuity, nor were they required to be. Cable and airplane witness marks were consistent with the nose landing gear first striking the transverse cable, and the right wing and main landing gear subsequently striking the parallel cables. The airplane came to rest about 270 feet south of the transverse cable strike location. The airplane came to rest inverted, with the fuselage oriented about 45 degrees from horizontal. The approximate at-rest heading was 220 degrees magnetic. Aside from multiple small window and plastic fragments, no components had separated from the airplane. The engine was displaced up, aft, and left in the airplane axis system. The two blade fixed pitch metal propeller remained attached to the engine. Cockpit occupiable volume was significantly compromised forward of the front seats. The right wing displayed leading edge crush damage at the outboard-most 3 feet of its span. The left wing exhibited tip crush and fragmentation damage. The flaps were found extended to the full-down landing position of 40 degrees. Both wings and both flaps exhibited crush damage in the lateral direction in their aft inboard regions, and the upper aft fuselage exhibited corresponding crush damage in the region of the rear window. The fuselage exhibited slight buckling towards the aft end of the cabin. The aft fuselage, tailcone, and empennage were essentially undamaged. All airplane components, including all flight controls, were accounted for at the site. Control cable continuity was established throughout the airplane. A Lowrance AIRMAP 1000 GPS, was recovered from the wreckage and sent to the NTSB Recorders Laboratory in Washington, DC for data download. Damage to the device, plus the unit's data storage protocols, prevented development of an airplane flight track time history. Additional details are provided in a separate report in the public docket for this accident. Examination revealed that a supplemental electrical system installed to provide power for the radar equipment and associated test equipment had overheated and began to burn. No evidence of overheating or fire was observed on any wiring or electrical components of the airplane itself; thermal damage was confined to the operator-installed electrical system and airplane furnishings (carpet, sidewalls, etc). The airplane and components were recovered and transported to a secure facility for additional examination. Refer to the public docket of this accident for additional details. ADDITIONAL INFORMATIONIMSAR Equipment IMSAR was a designer and manufacturer of synthetic aperture radar systems that were primarily intended to be used on airborne platforms, primarily by the Department of Defense (DoD), and often as externally-mounted pods. The company used its two Cessna airplanes as low-cost platforms for portions of the airborne development and testing of the radar equipment. In order to provide for the electrical power needs of the various radar systems and support equipment being tested or used on the Cessnas, and also to enable those devices to be ele
***This report was modified on August 18, 2015. Please see the docket for this accident to view the original report.*** The operator's improper installation of a supplemental electrical power supply, which caused a short circuit due to inadequate vibration and abrasion protection, which resulted in chafing of the wires, which contacted one another, short-circuited, and caused an onboard fire. Contributing to the accident were the installation of the supplemental electrical power supply system without the supervision of an FAA-certified mechanic, the lack of an onboard means for fire suppression, and the pilot's inability to see the low-conspicuity power lines across the landing approach path until it was too late to take evasive action.
Source: NTSB Aviation Accident Database
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