A Navy investigation says an August helicopter crash off the coast of San Diego was not pilot error, but was caused by the mechanical failure of a hose funneling hydraulic fluid to the helicopter’s rotor.
The 23-page command investigation by the Navy’s 3rd Fleet was released Tuesday, and chronicles the events during the 2.5-hour training flight that led up to the Aug. 31 crash of the MH-60S Seahawk helicopter as it landed on the USS Abraham Lincoln during the third of four planned training exercises.
The aircraft fell into the ocean shortly after landing on the ship’s deck; five sailors died. One crew member was later rescued from the ocean alive.
The helicopter’s commander, Lt. Bradley A. Foster was from Oakhurst, California. Foster, 29, had 900 flight hours and 720 of those were logged in the Seahawk. He was in the Navy for more than six years.
The others who died were Lt. Paul R. Fridley, 28, a pilot from Annandale, Virginia; Naval Air Crewman (Helicopter) 2nd Class James P. Buriak, 31, from Salem, Virginia; Hospital Corpsman 2nd Class Sarah F. Burns, 31, from Severna Park, Maryland; and Hospital Corpsman 3rd Class Bailey J. Tucker, 21, from St. Louis.
All five belonged to the Helicopter Sea Combat Squadron 8 based at North Island, San Diego. The USS Abraham is also based out of San Diego.
“The investigation found that there is no evidence that pilot or aircrew error was a causal factor in the crash,” Cmdr. Zach Harrell, a spokesperson for Naval Air Forces, said.
Instead, investigators said in the report “the crash was caused by an in-flight failure of a damper hose, resulting in total loss of the main rotor damping, which led to severe vibrations upon touchdown.”
The hose feeds hydraulic fluid to the rotary assembly. If the hydraulic fluid is interrupted, it can cause instability in the rotor.
According to the investigators, all appeared normal aboard the helicopter and the pilots and hospital corpsman had completed three training scenarios, including medical training in the cabin and a search and rescue mission. Communication was good throughout the flight, the investigators said.
During the helicopter’s landing, visibility was 10 nautical miles and the wind was light over the flight deck. The ocean conditions were ordinary, and the flight deck was stable. The accident occurred during the third of four training events.
The aircraft had flown for nearly nine hours and successfully “hot-seated,” meaning that the helicopter had refueled and passed from one crew to another without shutting down its engines.
As the helicopter tried to land on the flight deck, it “experienced lateral and vertical vibrations,” investigators said. As vibrations intensified the helicopter “rotated 50 degrees vertically left and then 200 degrees to the right.”
Then the helicopter’s blade hit the flight deck and it fell into the ocean on the starboard side, sliding tail first.
Witnesses told investigators the helicopter’s approach to land appeared normal and that it hovered 10 feet over the ship before landing. As it touched down, vibrations inside “became violent and the noise level significantly increased during touchdown,” the report said.
As the helicopter went overboard, video from the flight deck showed the pilots’ doors were closed, the cabin doors were closed, and all the aircrew were restrained. A door near the gunner was open, which allowed one crewman to escape, Harrell said.
“The damper hose failed in-flight due to flattening of steel braid strands,” the investigators said in their report. “Bending the hose crushed wire braids into each other causing flattening and nicking that resulted in fatigue failure of the steel braid strands.”
Investigators said the hose likely failed over time as the helicopter logged more flight hours.
“Records dating back to 2011 do not document a yellow damper hose replacement and the flattening likely happened due to a one-time event at some point,” investigators concluded.
The report released Tuesday says the Navy has taken steps to prevent hose damage due to kinking from occurring in the future.
The helicopter and its crew were found 5,000 feet below the ocean’s surface on Oct. 8 by a Navy salvage and diving team from the HOS Bayou.
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