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Aircraft Malfunction, Insufficient Training Lead to KC-135 Crash, Three Fatalities

After its tail snapped off and an in-flight explosion, A KC-135 Stratotanker, like the one pictured here from McConnell AFB, Kan., crashed in the Kyrgyz Republic while on a combat aerial refueling mission May 3, 2013, because of both mechanical and human failures, according to the recently released accident investigation board report. The crash killed all three crewmembers and destroyed the nearly $40 million aircraft. (U.S. Air Force Photo/Senior Airman Armando A. Schwier-Morales/ Released)

After its tail snapped off and an in-flight explosion, A KC-135 Stratotanker, like the one pictured here from McConnell AFB, Kan., crashed in the Kyrgyz Republic while on a combat aerial refueling mission May 3, 2013, because of both mechanical and human failures, according to the recently released accident investigation board report. The crash killed all three crewmembers and destroyed the nearly $40 million aircraft. (U.S. Air Force Photo/Senior Airman Armando A. Schwier-Morales/ Released)

SCOTT AIR FORCE BASE, Ill. -- An aircraft malfunction and the aircrew’s insufficient training to handle such an in-flight emergency are among the factors that contributed to the May 3, 2013, crash of a KC-135 Stratotanker in the Kyrgyz Republic, according to the recently released Air Force accident investigation board report.

All three crewmembers — Capt. Mark Tyler Voss, 27, of Boerne, Texas; Capt. Victoria Ann Pinckney, 27, of Colorado Springs, Colo.; and Tech. Sgt. Herman Mackey III, 30, of Bakersfield, Calif. – perished in the mishap. They were en route from the Transit Center at Manas to Afghanistan on 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 a poor layout of key information in the in-flight manual and insufficient crew training as contributing to the mishap. The report said these factors detracted from the crew’s ability to act on critical information during their troubleshooting to turn off two cockpit switches, either of 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 report said. 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 report said.

According the investigation board, the subsequent, uncontrollable descent resulted in an in-flight explosion.

A unique combination of six factors — flight control malfunctions, insufficient crew force training, incomplete crew checklist response, use of rudder while in a Dutch roll condition, crew composition, and cumbersome procedural guidance — all came together during the flight’s short 11-minute duration and resulted in this accident, the board reported.

“The crew encountered a condition that they had not realistically experienced in training, and when coupled with decisions based on their relatively low recent experience levels, were presented with an unrecognized hazardous and difficult situation to overcome,” said Brig. Gen. Steve Arquiette, who led the accident investigation board.
The aircraft was assigned to the 22nd Air Refueling Wing at McConnell Air Force Base, Kan., and was flown by members of the 92nd Air Refueling Wing at Fairchild AFB, Wash. The crew and aircraft were flying out of the 376th Air Expeditionary Wing at the Transit Center Manas.



SIX FACTORS THAT CAUSED MISHAP
According to the accident investigation board, a half-dozen factors came together during the KC-135’s short 11-minute flight to contribute to the destruction of the aircraft and death of its three crewmembers.
• Flight control malfunctions
• Insufficient crew force training
• Incomplete crew checklist response
• Use of rudder while in a Dutch roll condition
• Crew composition
• Cumbersome procedural guidance