WPR22FA054

The instrument-rated pilot and three passengers departed on a night cross-country flight into instrument meteorological conditions (IMC). Automatic dependent surveillance-broadcast (ADS-B) flight track information indicated that the pilot departed and climbed the airplane to 495 ft mean sea level (msl), about 200 ft above ground level, before initiating a left turn. The airplane reached an altitude of 620 ft msl, then began a descent as the left turn continued. ADS-B data ended at an altitude of 395 ft about 660 ft northwest of the accident site. The airplane impacted flat, open terrain about 1 mile southwest of the departure end of the runway. The wreckage was fragmented and distributed in a manner consistent with a high-energy impact with terrain. All major structural components of the airplane were located at the accident site. Examination of the airframe and engine revealed no evidence of any preexisting anomalies that would have precluded normal operation. Review of weather information at the time of the accident indicated low cloud ceilings and restricted visibility due to mist, with ceilings near 300 ft above ground level and tops near 2,000 ft msl. The pilot obtained a weather briefing before departure. The night IMC present at the time of the accident were conducive to the development of spatial disorientation and would have made control of the airplane by visual references difficult, especially if the pilot encountered restrictions to visibility, such as clouds, during the transitional phase of flight after takeoff and initial climb. The left turn initiated at low altitude, the pilot’s failure to maintain the climb, the tightening, descending turn, and the subsequent high-energy impact are all consistent with the known effects of spatial disorientation. Therefore, it is likely that the pilot was experiencing the effects of spatial disorientation when the accident occurred. Postaccident toxicology testing revealed varying levels of ethanol in the pilot’s liver, kidney, and muscle tissue; a second lab did not report any ethanol in his muscle tissue. The ethanol concentration found in liver tissue was higher than the detected ethanol concentrations in kidney and muscle tissue. Isopropanol was also detected in liver tissue. Given the differing ethanol tissue concentrations, the state the body was recovered, and the presence of isopropanol in liver tissue, it is likely that the identified ethanol was from sources other than ingestion and did not contribute to this accident.

The FAA Civil Aeromedical Institute's publication, "Introduction to Aviation Physiology," defines spatial disorientation as a “loss of proper bearings; 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 IFR conditions, frequent transfer between visual flight rules and IFR conditions, and unperceived changes in aircraft attitude. The FAA’s Airplane Flying Handbook (FAA-H-8083-3B) describes some hazards associated with flying when the ground or horizon are obscured. The handbook states, in part, the following: The vestibular sense (motion sensing by the inner ear) in particular can and will confuse the pilot. Because of inertia, the sensory areas of the inner ear cannot detect slight changes in airplane attitude, 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. On December 4, 2021, about 1840 Pacific standard time (PST), a Beech V35 N7933M, was substantially damaged when it was involved in an accident near Visalia, California. The pilot and three passengers were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Recorded ADS-B data provided by the Federal Aviation Administration (FAA) showed that the airplane departed runway 30 at 1837:01 and climbed to 495 ft msl before entering a left turn. The data showed that at 1837:26, the airplane continued to climb in a left turn and reached an altitude of 620 ft msl before entering a descent. The data showed that the airplane continued descending in a left turn until ADS-B contact was lost at 1837:37, at an altitude of 395 ft, about 660 ft northwest of the accident site as seen in figure 1. The departing airport elevation was 295 ft msl. A witness located near the accident location reported that, while in her residence, she heard an airplane flying very low, followed by the sound of the airplane impacting terrain. While the airplane was flying overhead, the engine noise was constant and did not sound like it was malfunctioning. Concerned, she then notified first responders. Figure 1: View of airplane ADS-B track The Tulare County Coroner's Office, Tulare, California, performed an autopsy of the pilot. The pilot's cause of death was blunt trauma. Toxicology testing performed at the FAA Forensic Sciences Laboratory detected ethanol in the pilot’s liver (0.402 grams per hectogram [gm/hg]), kidney (0.045 gm/hg), and muscle tissue (0.035 gm/hg); no ethanol was detected in the pilot’s muscle tissue by another laboratory. Isopropanol was detected in his liver tissue at 0.009 gm/hg. The non-impairing cholesterol lowering medicationatorvastatin was detected in the pilot’s liver and muscle tissue. At 1830, the Visalia Municipal Airport (VIS) automated weather observation station reported wind from 280° at 5 knots, visibility of 2 ½ miles, mist, broken ceiling at 300 ft above ground level (agl), temperature 8°Cand dew point temperature 8°C, altimeter 30.24 inches of mercury. An AIRMET SIERRA advisory for instrument flight rules conditions was issued at 1245 and was valid at the time of the accident. The advisory identified ceilings below 1,000 ft, visibility below 3 statute miles, mist, and fog. No air traffic control services were provided to the pilot during the accident flight. A review of the pilot’s logbook showed that he completed an instrument proficiency check on March 24, 2021. In the 12 months preceding the accident flight, he accumulated about 4 hours of simulated instrument flight, 0.4 hours of actual instrument flight and about 1 hour of night flight. The airplane impacted a flat, open wheat field about 1 mile southwest of the departure end of runway 30. It came to rest on its left side, on a heading of about 265° magnetic, at an altitude of 290 ft mean sea level. The first identified point of contact with terrain was a ground scar/impression about 14 ft long, 22 inches wide, and 3 inches deep. The debris field extended about 345 ft to the main wreckage on a magnetic heading of 105°and was 200 ft wide. The propeller and propeller hub were located about 15 ft from the initial impact point. Flight control continuity was established from the cockpit to all primary flight controls. Numerous separations were noted within the flight control system consistent with signatures consistent with overload separation or due to recovery personnel during the recovery process. There were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.