WPR24FA124

The pilot’s continued use of the airplane’s autopilot after flight into moderate to severe icing conditions, which resulted in an exceedance of the airplane’s critical angle of attack and an aerodynamic stall.

The accident pilot had been in a recurrency training program in the accident airplane the week before the accident flight, which was the return flight after completing the week with the instructor. According to the instructor, the pilot wanted to proceed home so they had planned for the accident pilot to depart on that leg of the flight no later than 1830 for a route of flight that remained west of specific terrain due to weather forecasts and that would arrive at the destination airport before dark. The pilot subsequently departed about 30 minutes past the planned departure time and flew a route east of the terrain that had been discussed, which placed the airplane in severe weather conditions after dark. While descending from its cruising altitude, the airplane encountered turbulence and the autopilot disengaged. For the remainder of the flight, multiple transmissions were recorded between air traffic control (ATC) and the pilot regarding course corrections, altitudes, icing conditions, and issues with the airplane’s autopilot. ATC offered vectors from the arrival procedure; however, the accident pilot declined the vectors. After receiving another pilot’s report of airframe icing from ATC, the accident pilot confirmed to ATC that he had accumulated moderate rime ice and agreed when ATC offered a lower altitude. When ATC asked, the pilot confirmed that the airplane remained in icing conditions during the continued descent, and the airplane subsequently leveled at 7,200 ft above mean sea level (msl). ATC instructed the pilot to climb the airplane to the last assigned altitude of 7,400 ft msl; however, the airplane remained at 7,200 ft msl for 29 seconds and began a right turn. During flight at 7,200 ft msl, the airplane’s groundspeed slowed from 124 kts to 84 kts. ATC asked the pilot if he was ready to turn back to the left and the pilot responded “turning.” The airplane subsequently began a rapid descent from which the pilot did not recover. Recorded weather closest to the accident site reported wind from the southwest at 15 kts, with gusts to 23 kts, rain, and a cloud ceiling of 1,100 ft above ground level (agl). Multiple AIRMETS and SIGMETS were in effect throughout the planned route of flight, and areas of moderate to severe icing were forecast. The airplane flew its descent in instrument meteorological conditions and moderate to severe icing conditions, including supercooled liquid droplets (SLD). Given the conditions, the airplane likely encountered serious icing during the descent. The pilot continued to use the airplane’s autopilot system while flying in sustained moderate to severe icing conditions. It is likely that either the autopilot masked the effects of the ice accretion on the airframe until it either reached its limits of use and disengaged at a low attitude or that it remained engaged until the airplane exceeded its critical angle of attack and entered an aerodynamic stall. The sudden onset of a rapid descent and subsequent near-vertical impact are consistent with a loss of control due to an aerodynamic stall. Postaccident examination of the airframe and engines revealed no evidence of any preexisting mechanical failures or anomalies that would have precluded normal operation. Medical review indicated that the pilot had used a cannabis product and it is possible that he could have been experiencing associated impairing effects at the time of the accident. However, the exact timing of his last cannabis use or level of impairment could not be determined from muscle tissue results alone.

The operator provided an estimated flight time for the pilot of 3,100 total hours, 950 hours of which were within the previous year. According to the operator, the accident pilot had been working for the company as a contract pilot for about 18 months before the accident. The pilot completed recurrent training in the accident airplane on the day of the accident. According to the flight instructor who conducted the recurrency training, he provided the accident pilot ground instruction and flight training each day from April 9, 2024, to April 13, 2024. The training was treated “like an initial” at the operator’s request and included about 20 hours of both ground and flight instruction. At the conclusion of the training, the instructor discussed a return flight plan with the accident pilot that included departing SCK no later than 1830, flying a route that remained to the west of specific mountains due to weather forecasts, and landing at CNO before dark. The instructor assisted with providing overnight options for the accident pilot if he could not depart by 1830. Maintenance records for the airplane showed that the most recent maintenance was performed on February 15, 2024: a 12-month/150-hour periodic inspection, and reinstallation of the left engine. The airplane was equipped with a Collins AP 106 autopilot. According to Collins Aerospace, none of the system components contain nonvolatile memory. An autopsy of the pilot was performed by the San Bernardino County Coroner’s Office, San Bernardino, California, which listed the cause of death as multiple blunt impact injuries, and the manner of death as accident. Autopsy evaluation for natural disease was limited by the severity of injury. Toxicology testing performed at the FAA Forensic Sciences Laboratory detected delta-9-tetrahydrocannabinol (delta-9-THC) in muscle tissue at 5.5 ng/g and carboxy-delta-9-tetrahydrocannabinol (carboxy-delta-9-THC) in muscle tissue at 1.8 ng/g. No blood was available for testing. On April 13, 2024, about 2019 Pacific daylight time, a Gulfstream Corporation 695A airplane, N965BC, was destroyed when it was involved in an accident near San Bernardino, California. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot had planned to fly the airplane from Stockton Metro Airport (SCK), Stockton, California, to Chino Airport (CNO), Chino, California, following the completion of recurrent training in the accident airplane earlier that day. The airplane departed SCK about 1903 and climbed to a cruise altitude of flight level 250. The cruise portion of the airplane’s flight remained unremarkable. Review of official audio recordings from Southern California Terminal Radar Approach Control facilities and ADS-B flight track data revealed that, during the descent portion of the flight, about 2011, near the FLAVR waypoint, ATC asked the pilot to confirm that he was on the ZIGGY arrival and the pilot responded in the affirmative; however, the airplane’s autopilot had disengaged in turbulence, and he was course correcting. ATC acknowledged and issued a descent clearance to 12,000 ft msl. About 2012, ATC offered the pilot vectors and the pilot declined; he responded that he was correcting to join at the MAJEK intersection. About 2014, ATC relayed a previously received Pilot Report (PIREP) regarding icing and the accident pilot replied that he was in moderate rime icing conditions. ATC asked if the pilot wanted to descend to a lower altitude and the pilot responded in the affirmative. ATC issued a discretionary descent to 8,000 ft msl. About 2016, ATC asked the pilot if he was still in icing conditions during the descent and the pilot responded in the affirmative but indicated there was some improvement. ATC issued a continued descent to 7,400 ft msl. About 2017, ATC instructed the pilot to fly heading 185° and advised they could offer a lower altitude in a few miles. The airplane leveled at 7,200 ft msl. About 2018, ATC stated that the Ontario altimeter was 30.05 inches of mercury (inHg). The pilot asked ATC to repeat the last transmission and stated he was having issues with the airplane’s autopilot. ATC asked if he could turn the airplane back to the left and received a partial transmission of “...turning...” ATC advised the pilot that the minimum vectoring altitude was 7,400 ft msl and they appeared to be losing altitude rapidly. ATC issued a low altitude alert, and the last recorded ADS-B target was at 2018:47, at an altitude of 2,600 ft msl. An Alert Notice (ALNOT) was issued about 2035, and a ground search was initiated. The wreckage was located the next day by the San Bernardino County Sherrif’s Aviation Unit in steep sloping terrain about 20 miles northeast of CNO, at an elevation of 2,541 ft msl. When the airplane leveled at 7,200 ft msl, it maintained that altitude for 29 seconds, slowed from a groundspeed of 124 kts to 84 kts, and began a right turn. The final 3 ADS-B data points show the airplane in a further turn to the right: 6,800 ft msl at 56 kts, 5,200 ft msl at 36 kts, and 2,600 ft msl at 49 kts, respectively. Examination of the accident site revealed that the airplane impacted mountainous terrain near the top of a 45° sloping ridgeline, within a south-facing ravine. Debris was dispersed along both sides of the sloping ridgeline. The first identified point of contact (FIPC) with the ground was near the top of the sloping ridgeline. The portion of the debris field along the south-facing slope was about 260 ft from the FIPC and was oriented on a magnetic heading of 236°. The portion of the debris field along the north-facing slope was about 190 ft in length from the FIPC and was oriented on a magnetic heading of 286°. All major structural components of the airplane were observed throughout the debris field; they were recovered and exhibited extensive fragmentation and thermal damage. Both engines were recovered and exhibited extensive impact damage. Postaccident examination of the airframe and engines revealed no evidence of preimpact mechanical malfunction or failure that would have precluded normal operation. According to the Twin Commander’s Pilot’s Operating Handbook (POH), “Severe icing may result from environmental conditions outside of those for which the airplane is certificated. Flight in freezing rain, freezing drizzle, or mixed icing conditions (supercooled liquid water and ice crystals) may result in ice build-up on protected surfaces exceeding the capability of the ice protection system, or may result in ice forming aft of the protected surfaces. This ice may not be shed using the ice protection systems, and may seriously degrade the performance and controllability of the airplane.” The POH further states, “Since the autopilot, when installed and operating, may mask tactile cues that indicate adverse changes in handling characteristics, use of the autopilot is prohibited when unusual lateral trim requirements or autopilot trim warnings are encountered while the airplane is in icing conditions.” The section “Procedures for Exiting the Severe Icing Environment” includes the following: - Immediately request priority handling from Air Traffic Control to facilitate a route or an altitude change to exit the severe icing conditions, in order to avoid extended exposure to flight conditions more severe than those for which the airplane has been certificated. - Avoid abrupt and excessive maneuvering that may exacerbate control difficulties. - Do not engage the autopilot. - If the autopilot is engaged, hold the control wheel firmly and disengage the autopilot. If an unusual roll response or uncommanded roll control movement is observed, reduce the angle-of-attack. - Report these weather conditions to Air Traffic Control. According to the FAA’s Airplane Flying Handbook (FAA-H-8083-3C), “Anti-Icing/Deicing Equipmen