Chinook, MT, USA
N30921
Cessna 177B
While in cruise flight the aircraft suddenly lost all engine power, and after unsuccessfully attempting to get the engine restarted, the pilot attempted a forced landing on a nearby gravel road. During that attempt, the pilot failed to adequately compensate for strong crosswinds, and therefore inadvertently clipped the top of a tree that was located immediately adjacent to the approach end of the section of road he was trying to land upon. A post-accident inspection of the engine determined that the carburetor had separated from the engine in cruise flight, due to the fact that there were no longer any nuts on any of the four carburetor mount retaining lug bolts. The carburetor mounting flange holes all remained intact, and none of the four mounting bolts showed any signs of damaged or distorted threads. Recent use of Marihuana was determined to have impaired the pilot's judgment at the time he was attempting the forced landing.
HISTORY OF FLIGHT On October 9, 2003, approximately 1720 mountain daylight time, a Cessna 177B, N30921, collided with a tree during an attempted engine-out forced landing about five miles south of Chinook, Montana. The private pilot and one of his passengers received fatal injuries, and a second passenger received serious injuries. The aircraft, which was owned and operated by the pilot, was destroyed by a post-impact fire. The 14 CFR Part 91 personal cross-country flight, which departed Great Falls, Montana, about 50 minutes earlier, was being operated in visual meteorological conditions. No flight plan had been filed. There was no report of an ELT activation, and the ELT itself was destroyed by the fire. According to family members, the pilot and his front seat passenger flew from Poplar, Montana, to Great Falls earlier that morning in order to attend court proceedings that involved a member of their extended family. While in Great Falls, the pilot offered another individual, who had come to Great Falls from Poplar, in order to attend the same event, the opportunity to fly back to Poplar in his aircraft. This person eventually became the back seat passenger. The pilot and his two passengers returned to the Great Falls Airport around 1545, and according to Great Falls Tower personnel, the aircraft took off for Poplar at 1621. Recorded radar data shows that after takeoff, the aircraft made a left downwind departure and headed northeast, paralleling Highway 87. While en route, the pilot climbed to about 6,000 feet, and stayed within a couple hundred feet of that altitude until 1608:42. At that time the aircraft's mode C beacon indicated that it was at 5,800 feet, and located at 48 degrees, 28.07 minutes north, 109 degrees, 22.33 minutes west, and traveling at a ground speed of 132 knots. This was the last recorded radar hit. According to the surviving passenger (rear seat), the aircraft was in cruise flight when the engine suddenly quit without any warning. There were no unusual noises, vibrations, or smells prior to the loss of power. She also said that there had been no smoke, or comment from the pilot, or anything else that would have alerted her to the fact that the engine was about to stop producing power. She further stated that initially the pilot seemed to be very excited or a little panicky, but soon thereafter seemed to become calm, and began trying to restart the engine. Reportedly, the pilot attempted a number of times to get the engine restarted, but was unable to do so. As the aircraft descended, the pilot told the other occupants that he was going to land on a gravel road that he had noticed below. As the aircraft got closer to the ground, the pilot maneuvered toward the north end of a straight stretch of the road he had selected for the emergency landing. He then tried one more time to get the engine restarted, but after being unsuccessful, appeared to turn his attention totally toward landing on the gravel road. He ultimately entered a shallow left turn that brought the aircraft to a position that was essentially a close-in left base for an approximately 1,000 foot long straight stretch of the gravel road he had selected for the forced landing. As the pilot was making the final turn to land in a southerly direction on the road, the aircraft collided with the upper branches of a 40 foot high deciduous tree growing just off the east side of the road. According to the passenger, after hitting the tree the aircraft slowed significantly, spiraled down into the surface of the road, and then slid into an adjacent ditch on the west side of the road. Immediately after the aircraft came to a stop, a small fire started under the instrument panel, in the area near the pilot's feet. At that time, the back seat passenger exited the aircraft and attempted to walk, but quickly found it necessary to crawl because she had broken her back. Soon thereafter, the aircraft was engulfed in flames and was eventually consumed by the fire. METEOROLOGICAL INFORMATION The 1655 aviation surface weather observation (METAR) at Havre, Montana, which is located about 20 miles west of the accident site, reported clear skies, 10 miles visibility, and winds of 260 degrees at 19 knots. A witness to the accident, who was working on a farm about one-half mile north of the accident site, reported that it was clear in the area, and that there were strong gusty winds coming out of the west at what he estimated was about 20 miles per hour. Law enforcement officials reported that when they arrived at the scene about ten minutes after the crash, there were strong winds blowing almost directly across the road from west to east. WRECKAGE AND IMPACT INFORMATION Two main branches on the east side of the initial impact tree had been sheared off approximately 10 feet below the top of the tree. These branches were about four inches in diameter at the point where they had broken off. A number of smaller branches were scattered across the road along the track the aircraft traveled after impacting the tree, with the two largest pieces being found where the aircraft came to rest. Ninety feet past the tree, near the middle of the hard-packed road, on a magnetic heading of 260 degrees from the tree, there was a two inch deep impact crater that measured about one foot across. Scattered around that crater were about a dozen pieces of the aircraft's windshield. The main wreckage came to rest about 110 feet past the tree, just off the west side of the road, at 48 degrees, 30.600 minutes north, 109 degrees, 16.42 minutes west. The engine and fuselage were setting upright in a shallow depression, and pointing almost directly back across the road to the east. The wings, which had ultimately come to rest inverted, were laying almost exactly perpendicular to the fuselage. The aluminum structure around the engine compartment, the inboard half of both wings, and the entire fuselage until just forward of the empennage, was almost entirely destroyed by the intense post-impact fire. The outboard half of the wings and the empennage itself were the only clearly discernable aluminum structure remaining. The empennage, which was partially elevated off the ground by the wires of a barbed-wire fence, showed very little evidence of impact damage, and significant fire damage was limited to the portion of the empennage that was laying on the ground. Both propeller blades were bent aft about 30 degrees, and the outboard one-third of one blade and the most outboard six inches of the other had melted from the intense heat. The nose of the propeller spinner was crushed almost straight back, with no indications of rotational twisting. The engine itself showed no significant evidence of impact damage, but the lower part of the exhaust system, including the muffler, had been pushed almost directly aft about four or five inches. The primary structure of all the engine accessories had melted away, and the carburetor was found laying on the ground directly below the engine. The components of the flight control system had come loose from the rest of the structure as that structure melted away in the fire, but all control cables were traced, and all torque tubes, pulleys, and bell cranks were located and identified, and there was no evidence of any anomaly or lack of continuity in the flight control system. Once the wreckage was moved to an enclosed work space, the engine was subjected to a further teardown inspection. During that inspection the top spark plugs were removed from each cylinder, and they were determined to have normal electrode wear patterns, normal grayish-white coloration, and no evidence of mechanical damage to their electrodes or insulators. Compression was created in each cylinder by placing a thumb over the spark plug hole and rotating the crankshaft. The number two and three cylinders were bore scoped, and there was no evidence of detonation or excessive oil accumulation, and all four valves were intact. The number one and number four cylinders were removed from the crankcase, and there was no evidence of detonation, excessive oil accumulation, or valve degradation in those cylinders. With the number one and number four cylinders removed, their associated connecting rods, cam shaft lobes, and crankshaft throws were inspected, and there was no evidence of any mechanical damage, heat distress, or lack of lubrication. The oil screen was removed and found to be clean, with no evidence of metal contamination. The exhaust system was inspected and its coloration was the normal grayish-white, and there was no evidence of an oil residue. Because the carburetor, which had no readily apparent mechanical damage to its flange, was found laying below the engine at the accident site, the carburetor, the oil sump ( to which the carburetor attaches), and the muffler (which had been displaced aft into the area the front part of the carburetor normally occupies) were sent to the NTSB's northwest regional office for further inspection and examination. Further examination of these components revealed that there were no washers or nuts on the four carburetor flange attachment studs that extend out of the bottom of the oil sump. Before the soot was cleaned from these studs, they were inspected with both 10X and a 30X magnifiers, and no distortion or damage of the stud threads was detected. In addition, a strong magnet was passed closely by the surface of all four studs, and no ferrous metal particles were able to be collected. The four studs were then cleaned with a stainless steel brush, and the residue was collected. After the residue was removed, the studs were again inspected under magnification, and no distortion or damage to the threads was observed (see photo #6). The residue was again subjected to a magnetic field, and no metallic particles were collected. As a final step in the inspection of the residue, all of it was placed on a piece of smooth white paper and rubbed gently with a fingertip to feel for solid particles. None were found, and all of the residue was absorbed into the fiber of the paper. In addition, the carburetor mounting flange was inspected, and it was determined that the flange had not torn away at any of the four mounting holes (see photo #7). Although the left front hole was severely distorted by heat deformation of the flange (see photo #8), the other three holes maintained their shape. The right front hole (marked LF) and the left rear hole (marked RR) showed no distortion consistent with a partially mounted carburetor being forced aft and off of its studs (see photos #9 and #10). The right rear hole (marked LR) had a four millimeter long indentation along the very edge of its mounting surface lip that was consistent with an angular side force being applied by its mounting stud (see photo #11). The remainder of the left rear hole contour showed no other evidence of damage or distortion. It was also noted that the brass fuel filter cover cap, which on an undisturbed configuration sits directly behind the exhaust muffler, was not dented or disfigured (see photo #12). Although both the left side of the carburetor's oil sump mounting flange and the left side of its carburetor heat box mounting flange suffered distortion from the intense heat, inspection of the remainder of the body of the carburetor did not reveal any indication of discernable impact damage (see photo #13). Inspection of the muffler system prior to removal from the engine confirmed that it had been displaced aft about five inches, and that its most aft surface was now sitting in a location that normally would be occupied by the most forward three inches of the carburetor (see photo #14). It was noted that on the surface of the muffler shroud, directly in front of the two forward carburetor mounting lug bolts, there were two one-half inch wide dents in the shroud. At the very bottom of these dents (deepest point) were sharp-edged scars/gouges (see photo #15). With the muffler still on the engine, these scars were setting about one-half inch directly forward of the ends (tips) of the two aforementioned mounting lug bolts (see Photo #16). It was also noted that one of the two mounting bolts had been forced slightly aft (tilted, not bent), so that its tip was one-half millimeter more aft than its base. Where this bolt protruded from the oil sump case, impact forces had elongated the threaded lug hole so that there was a one-half millimeter space between the bolt body and the structure of the case. AIRCRAFT INFORMATION The last annual inspection was signed off on June 25, 2003. At that time the aircraft had accumulated 3,083.1 hours. During that inspection there was no maintenance work performed on the carburetor, and according to the individual who had performed the last six annuals on this aircraft, there had been no work involving the carburetor performed on this aircraft since the carburetor’s overhaul on July 16, 1981. At that time the aircraft had accumulated 2,193 hours. ADDITIONAL DATA AND INFORMATION An autopsy of the pilot was completed by the Pathology Department of Northern Montana Hospital, and the cause of death was determined to be accidental due to multiple traumatic injuries secondary to an aircraft crash. A forensic toxicology examination of the pilot was completed by the FAA's Bioaeronautical Sciences Research Laboratory, and it was determined that there was no detectable carbon monoxide or cyanide in the blood, and no ethanol in the vitreous fluid. The same examination made the following determination for legal and illegal drug screening: 0.0025 (ug/ml, ug/g) TETRRAHDROCANNABINOL (MARIHUANA) detected in the blood. 0.0141 (ug/ml, ug/g) TETRAHYDROCANNABINOL CARBOXYLIC ACID (MARIHUANA) detected in the blood. 0.0713 (ug/ml, ug/g) TETRAHYDROCANNABINOL CARBOXYLIC ACID (MARIHUANA) detected in the urine. The entire wreckage, to include the carburetor, oil sump, and the muffler, were released to Tracy Barrus, an officer of Phoenix Aviation Adjusters, Inc., on 11/14/03.
The total loss of engine power in cruise flight due to the separation of the carburetor from its mounting bolts, and the pilot's failure to adequately compensate for strong crosswinds while attempting the subsequent forced landing. Additional factors include strong crosswinds, a tree immediately adjacent to the gravel road that the pilot chose to land on, and the pilot's impairment due to recent use of Marihuana.
Source: NTSB Aviation Accident Database
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