What happened
On 3 May 2013, a KC-135R, registration 63-8877, crashed in the mountainous terrain approximately 6 miles south of Chaldovar, Kyrgyz Republic. The aircraft, operated by the 22d Expeditionary Air Refueling Squadron, was performing a mission to refuel coalition aircraft in Afghanistan before returning to the Transit Center at Manas.
Shortly after departure, the aircraft experienced an unexpected lateral shift in its heading. During the climb, the crew noted continuous rudder hunting, where the nose of the aircraft drifted slightly left and right. While the pilot noted difficulties with lateral control and suspected a potential yaw damper malfunction, the flight continued with the systems active. Roughly nine minutes into the flight, the aircraft entered a series of increasing yaw and roll oscillations, a condition known as a dutch roll, which the crew did not identify.
In an attempt to stabilize the aircraft, the co-pilot utilized manual aileron controls and briefly engaged the autopilot. While manual inputs initially prevented the oscillations from expanding, the use of the autopilot worsened the instability. The pilot eventually took manual control and attempted a left turn using left rudder. However, the forces generated by the dutch roll caused varying pressure on the rudder pedals, leading to a series of alternating rudder inputs that significantly intensified the oscillations. A subsequent right rudder input intended to roll out of the turn further aggravated the condition.
Findings
Investigation into the crash revealed that the malfunctioning yaw damper was a primary factor in the instability. The combination of this malfunction, the use of the autopilot, and the crew's rudder inputs during the unmanaged dutch roll created aerodynamic forces that surpassed the structural design limits of the aircraft. This caused the tail section to separate from the fuselage. Following the structural failure, the aircraft entered a high-speed dive, exploded in mid-air, and struck the ground at three separate locations. The accident resulted in 3 fatalities and the total destruction of the aircraft.