Schleicher Alexander Gmbh & Co ASH 26 E N50FU accident near Wellington, Colorado

Probable cause

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.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for CEN23FA391 for the full record.