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Final NTSB report concludes Citation pilot experienced spatial disorientation in 2021 crash into TN lake, killing 7

Photo of the accident plane by Alan Radeki, creative commons attribution 3.0 licenseOn May 29, 2021 the pilot flying a Cessna Citation I CE-501 (N66BK) lost control of the aircraft because of a type of spatial disorientation called somatogravic illusion and crashed into Lake Percy Priest shortly after takeoff, killing all seven on board. The Citation took off from Smyrna Airport (MQY) in Smyrna, Tennesse operating as a Part 91 flight. The pilot had filed an instrument flight rules flight plan, headed for Palm Beach International Airport (PBI). After being cleared for takeoff, the pilot was told to climb to and maintain 3,000 feet mean sea level (msl) and he initially read back the clearance as "at or above 3,000 feet" to which the controller corrected him, telling him to climb and maintain 3,000 feet instead. After takeoff, when the plane was about three miles north of the airport, the departure controller asked the pilot if the plane was "on frequency" and then after receiving a response instructed the pilot to turn right heading 130 degrees. The pilot did not acknowledge this, with the controller asking a minute later if he had copied the heading instruction. He responded with "130…Bravo Kilo."The flight path for the Citation A minute after this interaction the controller instructed him to climb and maintain 15,000 feet msl, but received no response. Multiple attempts were made to re-establish communications but there were no further responses, according to the report. Radar data shows that the pilot had contact with departure control until the time the radar track for the flight ended. Data revealed the plane had made a series of heading changes and several climbs and descents before entering a steep descending left turn. The last radar return showed the plane at an altitude of about 700 feet msl and descending at a rate of 31,000 fpm (feet per minute) on a heading of 090 degrees. This led the NTSB to believe the pilot was suffering from special disorientation. From the flight track data, the NTSB knew the plane entered the clouds and made frequent heading changes with climbs and descents before the final descending left turn. This maneuvering is often associated with a type of special disorientation called somatogravic illusion. A somatogravic illusion is a rapid acceleration that can produce the illusion of being in a nose-high altitude even when flying a straight and level flight. This illusion can prompt a pilot to lower the nose and enter a dive, or when in a deceleration have the opposite effect, thinking you are in a dive and raising the nose.RELATED STORY:9 Optical Illusions Every Pilot Should Watch For Because of the special disorientation, the pilot likely did not use his instrumentation during his takeoff and climb. This could have caused him to experience a high workload managing the flight profile and had an adverse effect on his flight performance. When the plane entered a high acceleration at an unusual altitude and entered into the descending left turn, the pilot was likely unable to recover. Witnesses fishing in the lake heard the sound of a jet before seeing the plane impact the lake straight down, with the nose hitting the water first. One witness described hearing an "extreme vertical acceleration for about 3-4 seconds" followed by a "boom" the report noted the witness described the plane sounding like a military jet. One witness also reported a very low ceiling mist at the time of the crash. Weather reported at MQY was wind from 310 degrees at ten knots, visibility of ten miles, overcast ceiling of 1,300 feet, temperature at about 57 degrees Fahrenheit, a dewpoint of 53 degrees Fahrenheit and a barometric altimeter setting of 30.04 in Hg. The pilot had a commercial pilot certificate with ratings for airplane single-engine and multiengine land and instrument airplanes. He also held a private pilot certificate with a rotorcraft-helicopter rating. The last FAA second-class medical certificate issued for the pilot was on Nov. 12, 2019 with a limitation ordering him to wear corrective lenses. He was not on any medication and had no known medical conditions at the time of the crash. He had logged 1,680.5 flight hours and of the total number of hours, 83 were in the accident plane. There were 39.8 hours of total instrument flight experience and 5.9 in the accident airplane. A previous flight instructor noted that he saw no issues with the pilot's ability to operate in instrument meteorological conditions (IMC) but he was more familiar with the navigation system installed on another plane he owned than the system on the accident plane. He had a check-ride with a designated pilot examiner (DPE) on March 11, 2020 and the DPE stated he had full confidence in the pilot's ability to operate the Citation in IMC. According to the logbook, the pilot had flown with another pilot on several occasions before obtaining his type rating. The other pilot said the accident pilot did not have issues operating the Citation or running through the checklist, but noted he struggled when operating in IMC and when using autopilot on the plane, saying it was a "...bit complicated and caused the pilot confusion." The report said the other pilot said in an interview that the accident pilot was "weak" when it came to flying IMC and often struggled with instrument approaches outside of his local flying area if he did not receive radar vectors onto an approach. He also stated that the accident pilot relied on his iPad to help him understand "time in space" and was told he was not proficient enough to operate in certain cities, like New York or Los Angeles. There was a pilot-rated passenger on board who had earned a commercial pilot certificate and rating for airplane multiengine land just two days before the accident. He only had a total of 310 flight hours on his FAA Airman certificate and/or rating application. He also held an instrument rating on his commercial pilot certificate and had private pilot certificate privilege ratings for airplane single-engine land and rotorcraft-helicopter. His last third-class medical certificate was issued on Nov. 16, 2017 and he was not type-rated for the Citation. The plane impacted two to eight-foot-deep water and was consistent with a plane traveling at a high rate of speed when it hit the water. A water sonar was used to find larger pieces of wreckage and underwater divers felt for debris. There was poor visibility and deep mud/silt on the lakebed that impeded the recovery process. About two-thirds of the wreckage was recovered, including the main cabin door, both engines, parts of the main cabin windows, all three landing gear and sections of both wings. Pieces recovered were examined and it was determined the plane was functioning normally, due to not finding a source of malfunction or failure or inconclusive findings. A simulation of the flight was performed and it was determined based on simulation calculations that the pilot could have perceived the aircraft as nose-up rather than nose-down during the descents. It was also found to be possible for the roll angle to have felt less extreme than it was. Because of the pitch and roll motions and the frequent changes in acceleration and deceleration, the pilot's vestibular system which allows the inner ear to have a sense of balance and spatial orientation, might have been disrupted. When this happens, it can be difficult to distinguish between load factors due to motion versus those due to gravity. The inner ear alone is unable to differentiate between a tilt and an acceleration and other factors like visual cues are needed. The instrument-rated pilot likely had limited visual cues due to the instrument meteorological conditions. The FAA's Pilot's Handbook of Aeronautical Knowledge states that "a rapid acceleration, such as experienced during takeoff, stimulates the otolith organs in the same way as tilting the head backward." "This action may create what is known as the "somatogravic illusion" of being in a nose-up attitude, especially in conditions with poor visual references. The disoriented pilot may push the aircraft into a nose-low or dive attitude. A rapid deceleration by quick reduction of the throttle(s) can have the opposite effect, with the disoriented pilot pulling the aircraft into a nose-up or stall attitude."
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