After dropping a load of skydivers, the pilots were returning to the airport to pick up another group of skydivers, with the second-in-command (SIC) as the pilot flying. The pilot-in-command (PIC) indicated that the approach was stabilized until the airplane descended below the tree line and encountered what he described as windshear. The SIC initiated a go-around; however, before he could arrest the airplane’s sink rate and establish a climb, the right main landing gear impacted the runway surface and separated from the airplane. The crew declared an emergency, reported the loss of the right wheel, and requested to divert to a larger airport. During this diversion, the crew planned the landing, and the SIC communicated with air traffic control (ATC) while the PIC flew the airplane.The PIC reported that, about 20 minutes into the diversion, after conducting approach and emergency briefings, the SIC became visibly upset following the hard landing. The PIC described that, about this time, the SIC opened his side cockpit window and lowered the ramp in the back of the airplane, indicating that he felt like he was going to be sick and needed air. The PIC stated that the SIC looked at him and said he was sorry, got up from his seat, removed his headset, and ran out of the airplane via the aft ramp door. The PIC subsequently notified the controller that the copilot had just jumped out of the back of the airplane without a parachute. The PIC subsequently performed a successful emergency landing.Although the PIC and operator reported that the SIC’s departure from the airplane was an intentional act, there was insufficient information to support that assertion. No family or company personnel shared concerns about the SIC’s state of mind or behavior until the events that resulted in his departure from the aircraft; however, a company pilot shared an event during which the SIC had seemed to have a disproportionate, intense emotional and physical reaction upon becoming worried that he had lost a fuel payment card. The operator and family Page 2 of 11 ERA22LA348also indicated that the SIC felt that the accident flight with the PIC, who was also the chief pilot for the operator, was very important. This would have added to the SIC’s stress and emotional response after the hard landing, during which he was the pilot flying. In the 20 minutes of flight while serving as the monitoring pilot, the SIC was actively engaged in communicating with ATC, reviewing emergency procedures, and providing recommendations to the PIC on the landing runway at the diversion airport.In his initial statement to authorities, the PIC stated that, before departing the airplane, the SIC became visibly upset and apologetic, and reported feeling sick. His actions to increase ventilation in the cabin, which included opening the window and lowering the ramp, as well as his hurried departure from his seat, are consistent with an attempt to address increasing nausea symptoms and a desire to not throw up in the cockpit. However, the SIC made an unsafe decision to run to the rear of the cabin with the ramp in a fully lowered position, as he likely had not previously been in the cabin in flight with the ramp down. It is possible in his haste he lost his footing when encountering the area of the ramp and inadvertently fell from the airplane. Weather sounding and radar data supported the potential for windshear and turbulence activity, and the PIC reported that there had been moderate turbulence during the flight. The postaccident toxicological finding of mitragynine in the SIC’s liver tissue and urine indicated that he had used a kratom product, which had the potential to cause impairment. Notably, anxiety control was a common motivation for kratom use, and anxiety itself may predispose people to heightened physiological responses to stress, which sometimes manifest with nausea, dizziness, or feeling hot or smothered. Although it is possible that effects of kratom may have contributed to nausea or to some dizziness or perceptual impairment that may have increased his risk of falling, there is insufficient evidence to determine whether effects of the SIC’s kratom use contributed to the accident.