Last updated: 30 June 2016
Narrative:A US Air Force Boeing KC-135R Stratotanker aircraft left Bishkek-Manas Airport at 14:30 LT for a combat aerial refueling mission.
Upon takeoff, a flight control system malfunction, the board found, generated directional instability, causing the aircraft's nose to slowly drift from side-to-side or "rudder-hunt." This condition, not fully diagnosed by the crew, progressed into a more dangerous oscillatory instability known as a "Dutch roll." The board identified that a poor layout of key information in the inflight manual and insufficient crew training contributed to the mishap by detracting from the crew's ability to act on critical information during their troubleshooting to turn off either of two cockpit switches which may have eliminated the malfunction.
Having not recognized the Dutch roll condition, the crew initiated a left turn to remain on-course along the planned route of flight and used a small amount of left rudder to coordinate the turn. The use of rudder, while in a Dutch roll, increased the aircraft's oscillatory instability. The ensuing large side-to-side movements of the aircraft varied the crew member's foot pressure on the rudder pedal which caused inadvertent fluctuations in rudder position. These fluctuating rudder movements, coupled with slight right rudder use while rolling out of the turn, compounded the Dutch roll severity and produced extreme airframe stress that caused the KC-135's tail section to separate from the aircraft. The subsequent, uncontrollable descent resulted in an in-flight explosion.
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