Shell 77 crew encountered a condition they had not realistically experienced in training, which left them with an unrecognized hazardous situation that was difficult to overcome.
On May 3, 2013, a KC-135R, call sign Shell 77, crashed in the foothills of mountains located six miles south of Chaldovar, Kyrgyz Republic. The aircraft was assigned to the 22d Air Refueling Wing at McConnell AFB, Kan., and was flown by members of the 92d Air Refueling Wing at Fairchild AFB, WA. The crew was flying out of the 376th Air Expeditionary Wing at the Transit Center at Manas.
The crew was departing from the Transit Center at Manas to Afghanistan on a combat aerial refueling mission. The aircraft exploded in flight, impacted the terrain at three main locations, and burned, costing the lives of Capt Mark Tyler Voss, Capt Victoria A. “Tori” Pinckney, and TSgt Herman “Tre” Mackey III.
According to Air Mobility Command (AMC) Accident Investigation Board (AIB), immediately after takeoff, a flight control system malfunction generated directional instability, causing the aircraft’s nose to 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 “Dutch roll.”
The AIB identified that a poor layout of key information in the flight manual and insufficient crew training contributed to the mishap by detracting from the crew’s ability to act on critical information while troubleshooting. The AIB found the crew did not recognize the Dutch roll condition, initiated a left turn to remain on course, and used the left rudder to coordinate the turn, thereby increasing the aircraft’s oscillatory instability. The ensuing severe side-to-side movements of the aircraft varied the crew member’s foot pressure on the rudder pedal, which caused inadvertent fluctuations in the rudder position. These fluctuations, coupled with 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.
A combination of factors–flight control malfunctions, insufficient crew force training, incomplete checklist response, use of rudder while in a Dutch roll condition, crew composition, and procedural guidance–all came together during the flight, resulting in this accident. The crew encountered a condition they had not really experienced in training, which left them with an unrecognized hazardous situation that was difficult to overcome.
“Our hearts go out to the family members and friends of these Airmen,” said Brig Gen Steve Arquiette, who led the accident investigation board. “Having attended the memorial service at Manas and later interviewed many co-workers, I know these Airmen were highly regarded and are greatly missed. The investigation team, with the help of our industry and Kyrgyz government partners, pushed through months of intense fact-finding for the primary purposes of understanding what happened that day and to honor the crew’s service to our nation.”
The AMC way forward was clear–making immediate changes and improvements to checklists, to procedures, and to simulators. Specific actions included revised crew procedures for unscheduled rudder deflection and modifying KC-135 flight simulators and training syllabi to better prepare aircrews for Dutch roll and lateral flight control events. The command was also working with the airplane manufacturer and the AF Lifecycle Management Center to rewrite flight manual sections and conduct an in-depth analysis of rudder system components to develop components and T.O. improvements. AMC plans to continue to refine and implement solutions to prevent any repeats of this tragedy and ensure the KC-135 remains a safe, effective, and capable aircraft for many years.
Photo by U.S. Air Force