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Malfunction, pilot error caused May KC-135 crash

Mar. 13, 2014 - 06:00AM   |  
KC-135 refuels F-35
A KC-135 Stratotanker flies over Edwards AFB. (Senior Airman Julius Delos Reyes / Air Force)
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A flight control system malfunction and subsequent pilot error ultimately brought down a KC-135 Stratotanker on May 3, minutes after takeoff from Manas Transit Center, Kyrgyzstan, an Air Force accident investigation report released March 13 shows.

All three Fairchild Air Force Base, Wash.-based, crew members onboard perished in the crash: pilot Capt. Mark Tyler Voss, 27, of Boerne, Texas; co-pilotCapt. Victoria Ann Pinckney, 27, of Colorado Springs, Colo.; and boom operator Tech. Sgt. Herman Mackey III, 30, of Bakersfield, Calif.

The trouble began just after takeoff at 2:37 p.m., according to the accident report. The pilot and co-pilot, in communications with controllers, described the aircraft, which was headed for a refueling mission in Afghanistan, as “kind of waffling” and getting difficult to fly.

A bent lock lever in the power control unit caused the initial slow, erratic drifting, which soon grew into a dangerous “Dutch roll” of the plane — rocking side to side and pitching up and down, according to the report. The relatively inexperienced crew did not recognize the roll, which got worse as they turned the plane left toward its flight path. “Extreme airframe stress” caused the plane to separate at its tail section, leading to an in-flight explosion as the aircraft plummeted into the sparsely populated foothills of the Himalayas.

The plane broke into four pieces scattered across a 6-mile-wide debris field near where local villagers grazed cattle and sheep.

A poorly organized inflight manual, which warned against some of the pilot’s and co-pilot’s maneuvers as the plane began to oscillate — they switching briefly to autopilot and used the rudder to turn the Stratotanker — compounded the problem, Brig. Gen. Steven Arquiette, accident investigation board president said in an accident report briefing.

“I don’t believe the Dutch roll would have gotten worse on [its] own,” he said.

The airmen also were not properly trained to recognize and respond to the dramatic oscillations, which detracted “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,” the report said.

“The crew, if it had taken proper actions, most likely would have prevented this outcome,” Arquiette said.

The crew was fully qualified, well-rested and in good spirits on the day of the crash, he said. But they had “relatively low overall experience.”

Voss had become a command pilot just seven weeks before he deployed. Pinckney, the co-pilot, and Mackey, the boom operator, had both re-qualified on the KC-135 less than two months before deploying to the Middle East. Before that, Mackey had spent nearly four years on non-flying duty; Pinckney re-qualified after 10 months off.

Teams of experts and investigators spent months analyzing what Arquiette described as a highly complex crash, the results of which were shared last month with the family members of the lost crew.

The plane had no structural problems, he said. It underwent unscheduled maintenance less than three months before the crash for “rudder hunting,” the slow drifting back and forth the crew first reported on takeoff. The aircraft went on to fly 14 more times before the May 3 mishap.

Safety improvements are underway, he said, including beefed up Dutch roll recognition and recovery training and updated and expanded flight manual publications. Modifications are also underway for the KC-135 simulator, which was “incapable of realistically training crews for this type of situation,” Arquiette said.

The Air Force is also evaluating the rudder system.

“It’s very important to note this airplane the Air Force will continue to fly for the next decade,” Arquiette said.

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