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Malfunctioning equipment, crew experience and training contributed to Shell 77 crash

Malfunctioning equipment, crew experience and training contributed to Shell 77 crash

SPOKANE, Wash. - A cascade of problems, from malfunctioning equipment to crew training and experience led to the catastrophic loss of a KC-135 over Kyrgyzstan last May and the deaths of three Fairchild Air Force Base airmen.

Air Mobility Command released its Accident Investigation Board report into the crash of Shell 77 Thursday morning in an online briefing presented by Brig. Gen. Steven Arquiette, the Inspector General for Headquarters Air Mobility Command at Scott Air Force Base, Ill.

That report detailed a series of events that led up to the crash of the KC-135 and the deaths of Capt. Mark T. "Tyler" Voss, Capt. Victoria A. "Tori" Pinckney, and Tech. Sgt. Herman "Tre" Mackey III.

The three airmen died on May 3, 2013, when their tanker crashed 11 minutes after their departure from the Transit Center at Manas on a refueling mission in support of Operation Enduring Freedom.

The Flight

The tanker took off from Manas at 2:37 p.m. local time, 18 minutes before scheduled takeoff time, which was not unusual, Arquiette said. The forecast for takeoff included isolated thunderstorms and the cloud deck was at 12,000 feet.

Upon takeoff the tanker experienced an immediate "crab" to the right; the pilot -- Capt. Voss -- said the aircraft was "waffling a lot." Soon afterward the aircraft went into a Dutch roll, a type of motion where the aircraft wags its tail while rocking from side to side. At approximately seven minutes into the flight the co-pilot, Capt. Pinckney, began to make "corrective action" to compete with the Dutch roll.

"It motions back to the left. The left wing now has more wind over it and it begins a turn to the left and this situation just goes back and forth in a oscillatory manor until it's either dampened out or it will grow into a more severe case which it did in this case here," Arquiette said.

The crew also attempted to engage the autopilot twice and on both occasions the oscillations of the aircraft increased. Voss also knew there were issues with the Series Yaw Damper but did not shut it off.

"The malfunction aggravated itself further into the flight," retired Air Force Lt. Col. Dale Storr said. "They attempted to resolve it with the autopilot; that only made the situation worse. They analyzed the situation the best they could with the training and information they had from their manuals, it didn't seem to help them."

Storr, who retired from flying KC-135 tankers with the Washington Air National Guard several years ago, knows all too well what its like to fight to keep your plane in the air. While running a combat mission into Kuwait as an A-10 Warthog pilot during Desert Storm, Storr was shot down and spent 31 days as a prisoner of war.

"With improper control inputs it just aggravates to start (making it sway) more and more and the nose starts sliding more and more. With proper control inputs you'll dampen the Dutch roll out and it will go to zero and the airplane will fly normally," he added.

Ten minutes into the flight Voss took control of the aircraft from Pinckney. The aircraft was in a more pronounced Dutch roll and he started using the rudder to regain control. Both Voss and Pinckney were being rocked back and forth in their seats, but Voss maintained pressure on the rudder input with his left foot as he was rocked in the cockpit.

As this was happening, Voss shifted slightly from left to right rudder and within 20 seconds there was a drastic effect on the tail section. A combination of the Series Yaw Damper malfunctioning, coupled with the flight crew's attempts to engage the autopilot followed by the use of the rudder increased the Dutch roll the plane. The subsequent accident investigation revealed there were 20 rudder movements on the aircraft as the flight crew tried to correct the Dutch roll, with the side slip worsening each time.

The tail section was ripped from the rest of the aircraft and the plane began plummeting to the ground.

"Balance is provided by the tail section. So as the tail section is now removed, the natural tendency for the airplane is to pitch down and at this point once the tail section is (gone) the airplane pitched down at 82 degrees nose low," Arquiette said.

At 10,000 feet, with the aircraft in an 82-degree dive, the right wing ripped away the fuselage, exposing fuel in the wing tank which triggered an explosion.

At 2:48 p.m. local time, 11 minutes into the flight, Shell 77 crashed into the ground. Voss, Pinckney and Mackey were killed in the crash.

The Crash Investigation

Air Force officials report the debris field was approximately 10 miles in size, with the tail section being found a mile and a half from the main crash site, which was about 2.5 miles in diameter. It took 16 days to collect all of the debris from the crash field.

The investigation into the crash, which took nearly a year to complete, found there were a number of factors that contributed to the crash. Arquiette cited there were "organizational training problems" on the training of Dutch roll recovery procedures as well as handling problems related to the Series Yaw Damper. In both cases the training was "insufficient."

Additionally, Arquiette noted that "the KC-135 simulator was incapable of realistically training crews for this type of situation." He added that this has since been updated for flight crews.

Another factor that hampered the safe recovery from the Dutch roll was that while the crew was qualified but "had little recency of experience" which "reduced situational awareness and detracted from safe operations."

Voss had recently upgraded to command pilot and was considered an extremely strong pilot. He had just under 1,200 hours in the KC-135 and nine hours as an aircraft commander. Pinckney had recently re-qualified after not flying for 10 months. She only four flights in the previous 15 months prior to deploying to Manas. Mackey recently re-qualified as a boom operator after nearly four years of non-flying duty. He had qualified for his position four weeks before the crash.

"They were an absolutely qualified crew, but they were a young crew," 92nd Air Refueling Wing commander Colonel Brian Newberry said during a media briefing held at Fairchild immediately following Arquiette's briefing. "They were ill-prepared to handle that. Were there different decisions that other pilots might have made? Perhaps, but for this crew and many other pilots would have made the same decisions, and they did the best."

All three crew members were medically qualified for flight status, there was no evidence of medication use, all three had adequate rest before the flight and were in good spirits before the mission, Arquiette said. The trio had deployed to Manas two weeks before the mishap.

There was "no evidence other than extreme overload that caused this aircraft to fail," Arquiette said. The aircraft had a tendency to roll to the right, and while it hadn't been written up by the crew, it had been experienced on a previous flight to Manas from RAF Mindenhall in England. The aircraft had been flown 14 times before the crash without a mishap.

The Air Force, as a result of the loss of Shell 77, has initiated a number of safety improvements, including improved training on Dutch roll recovery, flight manual updates, increased tracking of avionics malfunctions, modification of KC-135 simulator software, rudder movement monitoring development and rudder system evaluation.

"This was an accident that was caused because of mechanical error," Newberry said. "There were mechanical anomalies out there that resulted in Dutch roll characteristics that the crew was just not ready to respond to. They didn't have the training for it and our simulators aren't able to do that."

"Recommendations have been put forward that have immeasurably increased the safety of our vital KC-135 fleet. We will use these lessons of this tragic accident to better train our air crews, how do we respond and recognize Dutch roll," Newberry added.

"I'm convinced that it was an aircraft malfunction that was aggravated by the autopilot and may have been aggravated by some crew inputs, but only because they didn't recognize that it was a Dutch roll," Lt. Col. Storr said. "The problem is we've only been taught to see it in a simulator and as the Accident Investigation Board said, the simulator doesn't do a very good job of presenting the Dutch roll to our students. We need to improve that and they are."

"We did learn a lot from this accident and it's going to be implemented into training which is critical to prevent an accident like this from happening," he added.

The Air Force has met with the families of Voss, Pinckney and Mackey in recent weeks and briefed them on the details surrounding the crash of Shell 77. Arquiette said the familes expressed their thanks to the those who helped determine the cause of the crash.

While the fallen airmen returned home last May, Shell 77 is still overseas and is being prepared for its final transport back to the United States. Newberry said a new monument dedicated to Voss, Pinckney and Mackey will be unveiled on the one-year anniversary of their final, fatal flight.