The San Diego Union-Tribune
The fatal crash of a Navy MH-60S Seahawk helicopter after landing on the aircraft carrier Abraham Lincoln last summer was caused by a damaged component in the aircraft’s rotor, according to a Navy investigation released late Tuesday.
Investigators said they could not determine when the component — a damper hose — was damaged. The hose failed over time, the investigative report says.
Five sailors were killed in the Aug. 31 crash when the helicopter rolled off the flight deck into the sea. It was assigned to the San Diego-based Helicopter Sea Combat Squadron 8 at Naval Air Station North Island.
The aircraft and the remains of the sailors were recovered from the bottom of the Pacific Ocean in October from a depth of about one mile.
The helicopter was returning from a flight Aug. 31 — its third of the day, the Navy said — and showed no signs of mechanical problems in the air, the investigation found.
However, upon touching down on the Lincoln’s flight deck, the helicopter began experiencing “divergent and uncommanded vertical vibrations,” in what the investigation describes as a “ground resonance event.”
The result was that the helicopter lurched left then right when its rotor struck the flight deck, causing all four blades to detach from the rotor. Several sailors on the flight deck were injured from the resulting shrapnel, the investigation says.
The helicopter then rolled off the right or starboard side of the deck and plunged into the sea with six sailors on board — two pilots, two aircrew and two corpsmen. One of the aircrew was able to escape from the helicopter and swim an estimated 25 feet to the surface, the investigation says.
Five sailors were unable to escape the aircraft and were killed.
“The Navy continues to mourn the loss of Lt. Bradley Foster, Lt. Paul Fridley, Naval Air Crewman (Helicopter) 1st Class James Buriak, Hospital Corpsman 1st Class Sarah Burns, and Hospital Corpsman 2nd Class Bailey Tucker, and our thoughts and prayers go out to their families and loved ones,” said Cmdr. Zach Harrell, a Naval Air Forces spokesperson, in a statement.
According to the investigation, ground resonance events are a phenomenon of multi-bladed helicopters caused by the blades rotating off the aircraft’s center of gravity. The resonance increases over time in frequency and magnitude.
Navy investigators found that the wire braids in a single yellow damper hose had been crushed at some point during routine maintenance, damaging them in a way that eventually led to their failure.
“Fatigue failure of the steel braid strands is progressive,” the investigation says. “In other words, it takes flight time for the failure to occur. The time lapse between kinking and damper hose failure is highly dependent on numerous factors and is very difficult to determine.”
The helicopter entered service in 2011, the report says, and the yellow damper hose was never replaced.
However, in the weeks preceding the crash, two of the four color-coded damper hoses were replaced due to damage. The “red” hose was replaced on Aug. 3. The next day, the “blue” damper hose was also replaced.
The investigation concluded there were no maintenance discrepancies or supervisory negligence in the squadron.
As a result of the findings, the Navy issued new guidance for maintenance crews working around the damper hoses to avoid bending them or crushing them with the pry bar used to work on the rotor.
It also recommended a one-time replacement of all rotor damper hoses on its helicopters.
This story originally appeared in San Diego Union-Tribune.