Chuathbaluk, AK, USA
N1673U
CESSNA 207
The pilot departed on a positioning flight during dark night, marginal visual meteorological conditions. A witness, who was waiting for the airplane at the destination airport, stated that shortly after the pilot-controlled airport lighting activated, a snow squall passed over the airport, greatly reducing the visibility. The accident airplane never arrived at its destination, and a search was initiated. The airplane’s fragmented wreckage was discovered early the next morning in a wooded area, about 2 miles from its destination. A review of archived automatic dependent surveillance-broadcast (ADS-B) data received from the accident airplane showed that the pilot departed, and the airplane climbed to about 700 feet above ground level. The airplane remained at about 700 feet for about 3 minutes, and then entered a shallow right-hand descending turn, until it impacted terrain. On-site examination of the airplane and engine revealed no preaccident mechanical anomalies that would have precluded normal operation. The cockpit area was extensively fragmented, thus the validity of any postaccident cockpit and instrument findings was unreliable. Likewise, structural damage to the airframe precluded the determination of flight control continuity. A postaccident examination of the engine and recovered components did not disclose any evidence of a mechanical malfunction. Given the witness account of worsening weather conditions at the airport just before the accident and the lack of mechanical anomalies with the airplane, it is likely that the accident pilot encountered heavy snow and instrument meteorological conditions while approaching the airport. It is also likely that the pilot became spatially disoriented during the unexpected weather encounter and subsequently collided with terrain.
HISTORY OF FLIGHT On November 29, 2011, about 1925 Alaska standard time, a Cessna 207 airplane, N1673U, collided with terrain approximately 2 miles southwest of the Chuathbaluk Airport, Chuathbaluk, Alaska. The commercial pilot was fatally injured, and the airplane sustained substantial damage. The flight was being operated by Inland Aviation, Aniak, Alaska, as a visual flight rules (VFR) positioning flight under 14 Code of Federal Regulations Part 91, when the accident occurred. Night, marginal visual meteorological conditions (MVMC) prevailed at the time of departure, and company flight following procedures were in effect. The flight originated from the Aniak Airport about 1920. In a written statement to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), a witness who was waiting for the flight to arrive at Chuathbaluk stated that she had spoken to the pilot about 1800, and was told that the visibility was too low for him to depart Aniak. She spoke with the pilot again at 1905, and was advised that the visibility had improved enough for him to depart, so she drove to the airport to wait for the flight to arrive. She stated that the runway lights came on at approximately 1925, and at that time she could see the entire runway. About two minutes later, she said that the snow increased considerably, and that she could no longer see to the end of the runway. At 1940, the airport lights went off, and being concerned that the plane didn’t arrive, the witness called Inland Aviation again with no answer. Another person from the village told the witness that someone heard what sounded like an airplane crash nearby. The witness then contacted the Alaska State Troopers in Aniak, and a search was initiated. PERSONNEL INFORMATION The pilot, age 61, who was also the owner/director of operations for the carrier, held a commercial pilot certificate with airplane single-engine land, single-engine sea, multiengine land, and instrument airplane ratings. His last Federal Aviation Administration (FAA) second class medical was issued on August 7, 2011, with a limitation that he must wear corrective lenses. At the time of the last medical, he reported a total of 10,000 flight hours. The pilot’s personal logbooks were not available for review. His last CFR Part 135.293 airman competency flight check with a Federal Aviation Administration (FAA) inspector from the Anchorage Flight Standards District Office was performed on July 14, 2011, and was satisfactory in all areas of operation. On November 29, the pilot flew seven legs before the accident flight, all in the accident airplane. The first flight of the day initiated at approximately 1200. The pilot had a history of deficient vision in the left eye for which he was issued a Statement of Demonstrated Ability (SODA), and exotropia of the right eye, astigmatism, and early cataracts which were evaluated by the FAA Aerospace Medical Certification Division (AMCD). In addition, he had hypertension which was controlled with medication, and a below-the-knee amputation of the right leg for which he was issued a SODA by AMCD. AIRCRAFT INFORMATION At the time of the accident, the airplane had a total time in service of 16,888.9 flight hours. A review of the maintenance records showed that maintenance personnel completed a 100 hour inspection on the airplane the morning of the accident. The airplane was equipped with a Continental IO-520-F engine, rated at 300 horsepower. The engine had a total time in service of 5,841.7 hours at the last 100-hour inspection, and was overhauled approximately 835 hours prior to the accident. METEOROLOGICAL INFORMATION The closest weather reporting facility is the Aniak Airport, approximately 8 miles west of the accident site. At 1916, about 9 minutes before the accident, an Aviation Routine Weather Report (METAR) was reporting, in part: Wind 360 degrees (true) at 5 knots; visibility, 4 statute miles; sky condition, 3,600 feet overcast; temperature, zero degrees F; dew point, minus 8 degrees F; Altimeter, 29.55 in Hg. At 1936, about 11 minutes after the accident, the Aniak METAR reported: Wind, 360 degrees at 5 knots; visibility, 2.5 statute miles; sky condition, 1,500 scattered, 2,900 broken, 3,500 overcast. At 1956, the visibility was reported at 1.25 miles, and the ceiling was 900 feet broken and 1,300 feet overcast. The area forecast for the Yukon Kuskokwim Valley, valid until 0600 on November 30, called for isolated ceilings below 1,000 feet; visibility below 3 miles; with light snow, blowing snow, and mist. COMMUNICATIONS There were no communications with the accident airplane. WRECKAGE AND IMPACT INFORMATION On December 1, the NTSB IIC, an FAA operations inspector, and two Alaska State Troopers examined the wreckage site, but moderate snow, cold temperatures, and limited daylight restricted the available time at the scene. All the major components of the airplane were located within the wreckage path. The main wreckage was in an area of dense birch, and spruce trees. The average heights of the trees surrounding the accident site were in excess of 50 feet. The first observed point of impact was an approximately 70-foot tall spruce tree, situated 180 feet from the main wreckage. The initial impact point on the ground, approximately 31 feet from the main wreckage, was discernible by a disturbed area of snow-covered ground containing the airplane’s propeller, which had separated from the engine crankshaft. Numerous chopped and broken tree limbs were noted along the wreckage path. The path from the initial point of impact to the airplane’s point of rest was on a magnetic heading of approximately 120 degrees. At its point of rest, the airplane was suspended on top of numerous collapsed small birch trees. The nose of the airplane rested on the ground, and the empennage was suspended approximately 10 feet. Extensive impact damage was evident to the airplane's firewall, instrument panel, and cabin area. The throttle, propeller, and mixture controls were found in the full forward position, but their position at impact could not be determined, due to the control cables being pulled forward when the engine separated from the airframe. Due to impact damage, primary flight control continuity could only be established to the rudder and elevator. The right wing had extensive spanwise leading edge crushing. The inboard section of the right wing was separated from the fuselage attach points, and was displaced and rotated forward about 90 degrees. Approximately 5 feet of the outboard section of the right wing, along with the right aileron was suspended in a birch tree near the initial point of impact. The left wing remained attached to the fuselage, but was displaced aft about 30 degrees. The left lift strut was buckled about 2 feet from the mid-wing attach point. The outboard section of the left wing had extensive aft crushing, and approximately 4 feet of the outboard wing was torn off, and rested on the ground below the wing. The empennage was bent to the left just forward of the horizontal stabilizer. The right horizontal stabilizer was crushed inward from the tip, and the right elevator was buckled upward. The left horizontal stabilizer was mostly undamaged, but the left elevator separated from its attach points, and was located on the ground below the empennage. The top of the vertical stabilizer was crushed aft. The engine assembly was torn from the airplane's firewall, and came to rest approximately 15 feet beyond the main wreckage. Both the exhaust and induction system exhibited impact and crushing damage, and the folded edges of the exhaust tubes did not exhibit any cracking or bending. The oil sump was crushed against the bottom of the crankcase. The engine propeller separated from the engine just forward of the crankcase nose case seal. All three of the propeller blades remained in the hub. Two of the propeller blades displayed leading edge gouging, torsional “S” bending, and chordwise scratching. The third blade was bent slightly aft, and displayed chordwise scratching. MEDICAL AND PATHOLOGICAL INFORMATION A postmortem examination was conducted under the authority of the Alaska State Medical Examiner, Anchorage, Alaska, on December 1, 2011. The cause of death for the pilot was attributed to multiple blunt force injuries. The autopsy noted that the pilot had preexisting coronary artery disease without evidence of an acute heart attack. The FAA's Civil Aeromedical Institute performed toxicological examinations for the pilot on March 12, 2012, which was negative for alcohol. The toxicological examination revealed 15 percent Carbon Monoxide detected in the pilot’s blood, and an unspecified level of Cotinine in the blood. Cotinine is a metabolite of nicotine. Nicotine is found in cigarette smoke. The pilot was known to be a heavy smoker. According to a medical review of the toxicology, the levels of Carbon Monoxide detected in the pilot’s blood posed a low probability of impairment, and is likely a product of heavy smoking. SEARCH AND RESCUE After being notified that the airplane did not land in Chuathbaluk, and checking the Aniak airport and Inland Aviation hangar, search and rescue personnel from the Alaska State Troopers, and local volunteers, initiated a ground search for the missing airplane about 2030. About 2330, the Alaska Air National Guard Rescue Coordination Center notified the state troopers that the accident airplane had been tracked by the Alaska Radar System, a network of 16 long-range and three short-range military radar sites that provide Alaska air space surveillance, intercept control, and navigational assistance to military and civilian aircraft, and forwarded them the airplane’s last reported radar position. About 0145 the next morning, searchers located the airplane in an area of wooded terrain, just south of the airplanes last reported radar position, and confirmed that the pilot had sustained fatal injuries. TESTS AND RESEARCH On January 25, 2012, an engine examination was performed by Alaska Aircraft Engines, Anchorage, under the supervision of the NTSB IIC, and representatives of Continental Motors, Inc., and Cessna Aircraft Company. No anomalies, contamination, or evidence of malfunction were found in any of the engine accessories, excluding the magnetos and the vacuum pump, which were not on the engine during the inspection. The cylinders, pistons, valve train, crankshaft, and other internal components were all without evidence of anomaly or malfunction. On September 7, 2012, an examination of the airplanes’ attitude gyro, and directional gyro was performed by Aircraft Instrument Repair, Anchorage, under the supervision of the NTSB IIC. Both units were badly damaged with the housings dented in. The attitude gyro inlet filter was coated in a black residue. Markings inside the rotor housing appeared to have the same black residue. The rotor housing was intact with no damage to it, except one balancing nut shaft broken off, and one erection vane broken off. Opening of the rotor housing showed no conclusive signs that the unit was running at time of impact, and the rotor assembly was free to run with the bearings in operational condition. There were no markings on the dial face to indicate what attitude the unit was in upon impact. The directional gyro case was dented in badly, and had to be cut away to gain access to the internal assembly. The unit showed signs of the same black residue as the attitude gyro. Removing the rotor assembly from its housing showed it to have slight endplay in it, but was free to run. There were no conclusive signs that the unit was running at the time of impact. On September 7, the engine driven vacuum pump was disassembled by Avionics and Aircraft Systems, Anchorage, under the supervision of the NTSB IIC. The vacuum pump vanes were fractured, and the housing showed signs of rotation at impact. The frangible drive gear was not sheared during the impact sequence. No other preaccident anomalies were noted with the vacuum pump that would have precluded normal operation. ADDITIONAL INFORMATION ADS-B data and Flight Path The accident airplane was equipped with automatic dependent surveillance-broadcast (ADS-B) technology. In typical applications, the ADS-B capable aircraft uses an ordinary Global Positioning System (GPS) receiver to derive its precise position from the Global Navigation Satellite System (GNSS) constellation, and then combines that position with any number of aircraft parameters, such as speed, heading, altitude and flight number. This information is then simultaneously broadcast to other ADS-B capable aircraft, and to ADS-B ground, or satellite communications transceivers, which then relay the aircraft's position and additional information to Air Traffic Control centers in real time. A review of the ADS-B data received by the Anchorage Air Route Traffic Control Center (ARTCC), showed the airplane depart Aniak at 1920:24, climb to approximately 700 feet above ground level (agl), and proceed eastbound toward Chuathbaluk. At 1924:52, the airplane enters a shallow left turn, and at 1925:01 enters a shallow descending right turn until impacting trees at 1925:36. A copy of the airplane’s ADS-B flight track and data is available in the public docket for this accident.
The pilot’s loss of situational awareness after an inadvertent encounter with instrument meteorological conditions, which resulted in an in-flight collision with tree-covered terrain.
Source: NTSB Aviation Accident Database
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