CEN23FA391

The pilot’s loss of glider control during approach for reasons that could not be determined, which resulted in an aerodynamic stall at an altitude too low for recovery.

The 71-year-old pilot was operating the motor glider on a personal flight. The last transmitted flight track data showed the motor glider with a 60-kt ground speed and a GPS altitude of 5,948 ft, about 250 ft above ground level. The flight track data were consistent with the pilot conducting a glider landing-out maneuver after descending from 7,800 ft. The glider impacted terrain in a high-energy state, with a nose-down, near-vertical attitude. Postaccident examination of the glider revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Both flap control surfaces, aileron control surfaces, and the cockpit flap actuator were in the landing position. The glider manufacturer stated that a wing drop or aerodynamic stall will result in the glider losing a minimum of 100 to 200 ft of altitude and that nearly vertical, nose-down flight was possible, especially if the pilot did not quickly correct or gave the wrong control inputs during stall recovery. Postaccident toxicological testing of liver and urine samples from the pilot detected the drugs pioglitazone and citalopram. Pioglitazone is a prescription oral medication that may be used in the treatment of diabetes and is not considered typically impairing and likely did not pose a hazard to flight or contribute to the accident. However, the FAA requires case-by-case evaluation of the underlying condition and response to treatment before medical certification. Citalopram is a prescription medication commonly used to treat depression. Studies of citalopram have not established that it results in significant cognitive or psychomotor impairment. However, citalopram may carry a warning that any psychoactive drug may impair judgment, thinking, or motor skills, and that users should be cautioned about operating hazardous machinery, including motor vehicles, until they are reasonably certain that citalopram does not affect their ability to engage in such activities. Additionally, major depression can lead to cognitive impairment, particularly executive function. Pilots on citalopram seeking FAA medical certification are subject to case-by-case evaluation of the underlying condition and the response to treatment. Based on the pilot’s vitreous glucose, it is unlikely he was experiencing severe high blood sugar at the time of the accident. The vitreous and urine glucose results neither support nor exclude the possibility of low blood sugar. Other diabetes effects such as fatigue or blurry vision also cannot be excluded based on the results. There is no clear evidence that the pilot was impaired by the effects of diabetes or its treatment. Also, whether the underlying condition being treated with citalopram resulted in any impairing psychomotor effects at the time of the accident is unknown. The pilot’s cardiovascular disease increased his risk of experiencing a sudden impairing or incapacitating cardiac event, such as arrhythmia, chest pain, heart attack, or stroke. The autopsy does not provide specific evidence that such an event occurred; however, such an event does not leave reliable autopsy evidence if it occurs shortly before death. Pilots are not required to obtain FAA medical certification to act as pilot-in-command of a glider but are obligated to follow regulations that prohibit operations during medical deficiency and while using drugs that affect faculties in a way contrary to safety. It is likely that the pilot lost control of the glider, which then entered an aerodynamic stall at an altitude too low for recovery. The reason for the loss of control could not be determined.

The pilot’s flight history and hours of flight experience were obtained from his FAA medical certificate applications and Online Contest (OLC) Glider Logbook because his pilot logbook was not located. The OLC Logbook contained uploaded glider flights since 2007. The pilot’s last equivalent flight review was an annual check required for his Colorado Soaring Association membership. The Schleicher Alexander GmbH & Co ASH 26E motor glider is self-launching and of composite construction. It is equipped with an engine in the fuselage and a retractable propeller, which is mounted on a pylon that is raised and lowered out of the fuselage behind the cockpit. During normal operation, the propeller pylon is raised electrically to a vertical position before starting the engine. When the pilot is done using the engine to take off or obtain altitude, the propeller is stopped in a vertical position for stowing, and the pylon is then lowered to an engine cool-down position for a short time to allow cooling air to pass through the engine radiator. Once the engine is cool, the propeller pylon is stowed horizontally and faired in the fuselage. During postaccident examination, the propeller pylon was found in the engine cool-down position, but the propeller was horizontal, and no indication was found that the mechanism that holds the propeller vertical for stowing had been engaged. The manufacturer stated that the position was unusual. Although the manufacturer did not have operational experience with the propeller in this configuration, it presumed the position of the propeller would not have had a significant effect on the flight characteristics of the accident glider, based on its knowledge that the propeller pylon has a marginal effect on the glider’s flight characteristics in either the fully extended or engine cool-down position. The glider manufacturer estimated that recovery from an aerodynamic stall would result in a minimum altitude loss of 100 to 200 ft. The glider maintenance logbooks were not located. An autopsy of the pilot was performed by the Office of the Larimer County Coroner/Medical Examiner. According to the autopsy report, the cause of death was multiple blunt force injuries, and the manner of death was accident. The pilot’s last aviation medical examination was in 1999. He did not hold a current medical certificate. Medical certification is not required for glider operations. The pilot’s autopsy identified severe coronary artery disease, including 90% narrowing of the left circumflex coronary artery, 70% narrowing of the left anterior descending coronary artery, and 30% narrowing of the right coronary artery by plaque. Borderline left ventricular hypertrophy and hypertensive and diabetic kidney tissue changes were noted. The pilot’s autopsy report documented diabetes, hypertension, chronic kidney disease, atrial fibrillation, and congestive heart failure as conditions contributing to death based on history and autopsy findings. The specific source of each of these diagnoses was not explicitly stated. The FAA Forensic Sciences Laboratory also performed toxicological testing of postmortem specimens from the pilot. The pilot’s toxicology testing detected citalopram and its metabolite n-desmethylcitalopram and the diabetes medication pioglitazone. Vitreous glucose was normal. Urine glucose was 50 mg/dL. (Glucose in random fresh urine normally is 25 mg/dL or less, and it may increase due to high blood glucose or altered kidney function; the FAA Forensic Sciences Laboratory considers postmortem urine glucose above 100 mg/dL to be abnormal.) Vitreous chemistry performed by NMS Labs at the request of the Office of the Larimer County Coroner/Medical Examiner was notable for mild elevations of vitreous creatinine and vitreous urea nitrogen. Pioglitazone is a prescription oral medication that may be used in the treatment of diabetes. The medication is not typically impairing but carries some risk of adverse side effects, including low blood sugar. Pilots with diabetes on pioglitazone seeking FAA medical certification are subject to case-by-case evaluation of the underlying condition and the response to treatment. Citalopram is a prescription medication commonly used to treat depression. Although citalopram may carry a warning that any psychoactive drug may be impairing, studies of citalopram have not established that it results in significant cognitive or psychomotor impairment. Major depression can lead to cognitive impairment. Whether a condition being treated with citalopram resulted in any impairing psychomotor effects at the time of the accident is unknown. On August 31, 2023, about 1339 mountain daylight time, a Schleicher Alexander GmbH & Co ASH 26E motor glider, N50FU, was substantially damaged when it was involved in an accident near Wellington, Colorado. The pilot sustained fatal injuries. The glider was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Flight track data transmitted from an onboard recorder showed the self-launching motor glider departed to the northwest from the Owl Canyon Gliderport (4CO2), Wellington, Colorado, at 1320 (see figure 1). Figure 1. Flight track data from onboard recorder. During the climb, the pilot performed several turns, and the glider reached a maximum GPS-derived altitude of about 7,800 ft at 1330. The flight track data showed the glider then entered a steady descent on a northwest track, turned 180°, and flew southwest for about 2 miles before it turned back to the west. The last recorded position at 1339:43 showed the glider on a track of about 296°, with a ground speed of 60 kts and a GPS altitude of 5,948 ft, which was about 250 ft above ground level. The accident site was in a relatively flat agricultural field about 6 nautical miles northwest of 4CO2. The motor glider impacted the ground about 77° nose-down attitude, on a heading of 213°, about 900 ft north of the last position logged by the onboard flight recorder. The impact site consisted of a small circular depression and two ground scars that extended the length of the wingspan, consistent with the forward fuselage and both wing leading edges. The wreckage was located about 15 ft northeast of the impact site, upright, and oriented with the ground scar. Postaccident examination of the glider revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Flight control continuity from the control surfaces to the cockpit controls was confirmed. Both flap control surfaces, aileron control surfaces, and the cockpit flap actuator were in the landing position. Both wing airbrake surfaces were in the retracted position. The pilot’s lap belt was unlatched and located underneath the pilot, and the shoulder harness was unlatched and stowed on a fuselage shelf behind the seat. The propeller and driveshaft were in the cool-down position with no damage observed to the propeller blades. The propeller was perpendicular to the storage position and the propeller stop control was in the non-stop position. The engine throttle control was found in the idle position. The master switch position could not be determined due to impact damage. The LXNAV Nano 3 flight recorder mounted on the glareshield on a previous flight (see figure 3) was not located. However, its mount and attachment hardware were located in the debris field. Flight track data from the unit was recovered by a soring club. Figure 3. Cockpit instrument panel photograph uploaded by the pilot on a previous flight. The LXNAV Variometer, S/N 05708, mounted in the upper center of the instrument panel, was recovered and shipped to the NTSB Vehicle Recorder Laboratory for data download. However, due to data buffering, no additional flight track points could be recovered beyond the last transmitted flight track data point from the LXNAV flight recorder. Postaccident examination of