Kolb Company FIRESTAR KXP N4443G accident near Cave Junction, Oregon

Probable cause

The pilot's exceedance of the airplane's critical angle of attack during a turn, which resulted in an aerodynamic stall. Contributing to the accident was the pilot's use of potentially impairing substances with bipolar disorder, which resulted in a decreased reaction time during a stall recovery at a low altitude.

NTSB analysis

The pilot had recently installed an overhauled engine and decided to depart for a local flight. Witnesses observed that the pilot was in good spirits and that, after takeoff, the airplane turned left to the northwest, about 500 ft above ground level (agl). The airplane continued to turn left back towards the airport environment on a 30° to 40° bank angle (to the southeast). The witnesses stated that they saw the airplane descend about 100 ft in a slightly nose-down pitch attitude and subsequently entered a 90° nose-down attitude toward the ground. The airplane impacted the ground and came to rest in an open field, sustaining substantial damage to the fuselage and wings. Multiple witnesses confirmed that the engine was producing power. Examination of the wreckage did not reveal any mechanical anomalies to the airframe or engine.

The pilot’s toxicology results identified multiple potentially impairing substances including diphenhydramine, gabapentin, and venlafaxine, all of which may adversely and unpredictably interact with one another to cause sedation, decreased reaction time, and impaired cognition. Venlafaxine may induce mania in people with bipolar disorder if used on its own to treat depression without an additional mood stabilizing medication.

Based on information obtained from the patient’s family, the pilot had severe depression and bipolar disorder. The details of the pilot’s illness and his response to treatment are unknown. An episode documented by law enforcement the night before the accident was consistent with the pilot experiencing acute behavioral symptoms at that time. In people with bipolar disorder, the occurrence of acute symptoms decreases the threshold for further episodes, making the episodes occur more frequently if medical intervention is not provided. Additionally, bipolar disorder in people over 50 years of age increases the risk of cognitive defects including decreased executive function, impaired information processing speed, and impaired memory.

Additionally, bipolar disorder is a disqualifying psychiatric condition that is required to be evaluated by a Federal Air Surgeon. The pilot never reapplied for a medical after he allowed it to lapse in 2002 and there are no records he was evaluated.

With the available evidence, it is not possible to discern to what degree the effects of the medications used, as opposed to the pilot’s bipolar disorder, contributed to the accident. The pilot’s coronary artery disease placed him at some increased risk of a sudden impairing or incapacitating cardiac event, such as angina, arrhythmia, or heart attack, but there was no autopsy evidence that such an event occurred. However, such an event does not leave reliable autopsy evidence if it occurs immediately before death. Thus, whether the pilot's coronary artery disease contributed to the crash cannot be determined. The pilot's use of multiple potentially impairing substances and his bipolar disorder likely would have contributed to a diminished state of health during any attempts to recover the airplane after control was lost, given the pilot's experience with the airplane and the circumstances of the accident. The airplane was likely in an uncoordinated left turn (skid) as it turned back toward the airport. The lower (left) wing entered an aerodynamic stall initially during this skidding left turn, resulting in a nose-down pitch attitude, as is typical of straight-wing airplanes. The FAA suggests a margin of at least 1,500 ft agl for single-engine airplanes to recover from a full stall. Although the pilot was a certificated flight instructor and experienced pilot, his use of potentially impairing substances and medical history likely influenced his reaction time to recover from the stall at 500 ft agl. There was insufficient evidence to ascertain the specific recovery inputs the pilot implemented.

Text from the NTSB. Open the NTSB docket for WPR24FA104 for the full record.