CEN18FA037

The 89-year-old commercial pilot departed on a cross-country flight late on the day before Thanksgiving to visit relatives. He received two weather briefings in the 2 days before the flight, with the most recent briefing (the day before the flight) indicating widespread marginal visual flight rules conditions and mountain obscuration; the briefer advised the pilot that visual flight rules (VFR) flight was not recommended. Despite the conditions presented during the weather briefing, the pilot chose to conduct the flight under VFR and indicated to the briefer that he did not want to fly through clouds with potential icing conditions. GPS track data downloaded from a unit onboard the accident airplane indicated that the flight began uneventfully, with the pilot following a highway, likely for route guidance. As the flight progressed, the airplane's altitude began to decrease. This is consistent with the reported weather conditions and the pilot attempting to remain clear of clouds since he was not on an instrument flight rules flight plan and did not want to fly through the clouds. Near a location where the highway turned west through a town and around terrain, the airplane continued straight and flew along a valley between two ridges. The airplane made two turns within the valley, then made a left turn to the west, possibly in an attempt to return to the highway. While heading toward the highway and after crossing the ridge, the airplane entered a descending right turn. The GPS data ended about 750 ft from the accident site and indicated that the airplane was about 425 ft above ground level. Examination of the airplane, engine, flight controls, and instruments did not reveal any preimpact anomalies that would have precluded normal operation. Toxicology testing indicated that the pilot had used diphenhydramine, a sedating antihistamine, at some time before the accident; however, the blood level of the potentially impairing medication was below the therapeutic and impairing level. Therefore, it is unlikely that the pilot's use of diphenhydramine contributed to the accident. Based on the available information, it is likely that the pilot inadvertently encountered instrument meteorological conditions while maneuvering the airplane in deteriorating light conditions near the end of civil twilight. Although the pilot was instrument rated, no determination of his recent instrument flight experience could be made. He was likely not prepared for the sudden entry into instrument conditions and the loss of visibility combined with the turns and varying altitudes while attempting to exit the valley resulted in spatial disorientation and a subsequent loss of airplane control.

Spatial Disorientation The FAA Civil Aeromedical Institute's publication, "Introduction to Aviation Physiology," defines spatial disorientation as a loss of proper bearings or a state of mental confusion as to position, location, or movement relative to the position of the earth. Factors contributing to spatial disorientation include changes in acceleration, flight in IMC, frequent transfer between VMC and IMC, and unperceived changes in aircraft attitude. The FAA's Airplane Flying Handbook (FAA-H-8083-3A) describes some hazards associated with flying when the ground or horizon are obscured. The handbook states, in part: The vestibular sense (motion sensing by the inner ear) in particular tends to confuse the pilot. Because of inertia, the sensory areas of the inner ear cannot detect slight changes in the attitude of the airplane, nor can they accurately sense attitude changes that occur at a uniform rate over a period of time. On the other hand, false sensations are often generated; leading the pilot to believe the attitude of the airplane has changed when in fact, it has not. These false sensations result in the pilot experiencing spatial disorientation. The airplane, serial number 17254671, was manufactured in 1966 and was a single-engine monoplane with fixed tricycle landing gear and seating for four occupants including the flight crew. It was constructed primarily of metal and was powered by a Lycoming O-360-A4M, horizontally opposed four-cylinder engine, serial number L-36690-36A, rated to produce 180 horsepower. The airplane maintenance records were not available for review. The airplane was originally equipped with a Continental O-300-D engine rated to produce 145 horsepower. The airplane's airworthiness file did not reflect the installation of the Lycoming engine. On November 22, 2017, at 1656 eastern standard time, a Cessna 172G, N4676L, was destroyed when it impacted trees and terrain near Pittsford, Vermont. The pilot was fatally injured. The airplane was registered to Anne Kristine II, Inc., and was operated by the pilot under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. Night instrument meteorological conditions (IMC) existed near the accident site and the flight was operated on a visual flight rules (VFR) flight plan. The personal cross-country flight originated from Pittsfield Municipal Airport (PSF), Pittsfield, Massachusetts, at 1555 with the intended destination of Middlebury State Airport (6B0), Middlebury, Vermont. The pilot's son reported that the purpose of the flight was to visit relatives for the Thanksgiving holiday the next day. A hand-held Garmin 396 GPS receiver was found within the wreckage. Although the unit was damaged, track data for the accident flight was downloaded from the unit and depicted the entire accident flight. The airplane departed PSF at 1555 and traveled in a northerly direction until reaching Hoosick Falls, New York, where the airplane began to track northeast. The airplanecontinued on the northeasterly track until reaching Arlington, Vermont. After reaching Arlington, the airplane appeared to follow US Highway 7 for about 50 miles. During the initial portion of the flight, the airplane's altitude was generally at or above a GPS altitude of 3,000 ft. About 35 miles before the end of the recorded data, the airplane's altitude began to decrease. When the airplane was about 2 miles south of Pittsford, its altitude was about 1,500 ft agl. Before reaching the town of Pittsford, while still following Highway 7, the highway made a left turn toward the west through the town and around terrain, but the airplane continued its track toward the north. As the airplane continued north, with the highway to the west, it entered a valley between two ridges. After entering the valley, the airplane made a turn to the east followed by a turn to the north. These turns were within the bounds of rising terrain and ridge lines were on either side of the flight track. The airplane continued to follow the valley between the ridges in the terrain before turning toward the west. The airplane crossed the western ridge, then began a descending right turn toward the north, where the track data ended. The last recorded GPS position, about 14 miles from 6B0, was at 1,152 ft msl and about 750 ft from the accident site; the ground elevation at that location was about 727 ft. The Vermont State Department of Health, Office of the Chief Medical Examiner, Burlington, Vermont, performed an autopsy on the pilot. The cause of death was attributed to blunt impacts received in the accident. The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicology testing on specimens of the pilot. Diphenhydramine was detected in urine and cavity blood and ibuprofen was detected in urine. Diphenhydramine is a sedating antihistamine used to treat allergy symptoms and as a sleep aid. It is available over the counter under the names Benadryl and Unisom. Diphenhydramine carries the FDA warning: "may impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery)." According to the FAA toxicologist, the diphenhydramine level in the pilot's blood was well below therapeutic range and below the reporting curve. Ibuprofen is a non-sedating pain medication that is generally considered not to be impairing. The pilot received two weather briefings, one 2 days before the accident at 1814, and another the day before the accident at 1420. During the first briefing, the pilot was advised of a cold front moving through the area with scattered light precipitation, marginal visual flight rules (MVFR) conditions at best, and AIRMET Sierra for mountain obscuration likely. During the second briefing, the pilot indicated that he would like to fly VFR because he didn't want to fly through clouds with potential icing issues. The briefer advised the pilot of widespread MVFRconditions, current METARs, Terminal Aerodrome Forecasts (TAFs), AIRMETs, freezing levels, winds aloft, and that VFR flight was not recommended along the route of flight. The briefer also advised the pilot of mountain obscuration east and south of the intended destination, which would have included the accident site. AIRMETs Sierra, Zulu, and Tango were valid for the accident site at the accident time. The AIRMETs warned of IMC due to precipitation and mist; mountain obscuration conditions due to clouds, precipitation, and mist; moderate icing conditions below 7,000 ft; and moderate turbulence below 14,000 ft. At 1556, the recorded conditions at Southern Vermont Regional Airport (RUT), about 14 miles south-southeast of the accident site, included wind from 310° at 4 kts, 10 statute miles visibility, light rain, an overcast ceiling at 2,000 ft above ground level (agl), temperature 2°C, dew point 0°C, and an altimeter setting of 29.94 inches of mercury. At 1656, the conditions at RUT included wind from 310° at 6 kts, 6 statute miles visibility, light snow and mist, broken ceiling at 2,000 ft agl, overcast ceiling at 2,600 ft agl, temperature 2°C, dew point 0° C, and an altimeter setting of 29.94 inches of mercury. 6B0, the next closest airport with official weather information, was 14 miles north-northwest of the accident site; at 1635, 6B0reported wind from 340° at 4 kts, 10 statute miles visibility, broken ceiling at 2,200 ft agl, overcast ceiling at 3,400 ft agl, temperature 2°C, dew point 0°C, and an altimeter setting of 29.96 inches of mercury. At 1655, the conditions at 6B0 included wind from 350° at 5 kts, 10 statute miles visibility, scattered clouds at 2,200 ft agl, overcast ceiling at 3,600 ft agl, temperature 2°C, dew point 0°C, and an altimeter setting of 29.96 inches of mercury. Astronomical data indicated that the end of civil twilight occurred at 1657. The 89-year old pilot held a commercial pilot certificate with airplane single-engine land, airplane multiengine land, and instrument airplane ratings. His most recent third-class medical certificate was issued on July 14, 2015, with a limitation that the pilot must wear corrective lenses for near and distant vision; the medical certificate was not valid after July 31, 2017. At the time of the medical examination, the pilot reported 1,520 total hours of flight experience, and 55 hours in the 6 months preceding the examination. The pilot's flight logbook was not found in the wreckage and was not available for review during the investigation. Based on the pilot's age, his medical certificate would have been valid through July 31, 2017. He had not completed the requirements listed in 14 CFR Part 68, entitled "Requirements for Operating Certain Small Aircraft Without a Medical Certificate", also known as BasicMed as described in FAA Advisory Circular AC 68-1A. Examination of the airplane and engine did not reveal any preimpact anomalies. Details of the examination can be found in thedocket material associated with the accident investigation. Examination of the flight instruments recovered from the accident scene indicated that the airplane was equipped with both vacuum- and electrically powered gyroscopic flight instruments. An electrically powered artificial horizon indicator was found, as well as the face and external case of another artificial horizon indicator. The internal components of the second artificial horizon indicator were not located. The first artificial horizon indicator was disassembled; one of the gyroscope housing bearing mounting areas was fractured. Examination of the rotating core of the gyroscope and its cage showed evidence of circumferential scoring on both components consistent with rotation during the impact sequence. A vacuum-powered directional gyroscope was found and disassembled. The bearing mounts and the rotating core of the gyroscope were intact and did not show any evidence of the rotating gyroscope core having contacted the housing during the impact. A gyroscopic turn-and-bank indicator was found and was partially disassembled. Upon removal of the outer case, it was evident that the rotating gyroscope was intact and still turned freely on its bearings. No further disassembly was performed. The airplane's vacuum pump separated from the engine during the accident sequence. The vacuum pump was disassembled and internal examination revealed that the pump vanes were intact and no preimpact anomalies could be found.