Navy Helicopter Vibrated Before Falling Into the Sea, Report Says

A U.S. Navy helicopter that crashed off the coast near San Diego last week, killing five sailors, landed on an aircraft carrier and experienced vibrations before its main rotor struck the flight deck and the aircraft fell into the ocean, the Navy said in a safety report.

The MH-60S Seahawk helicopter had been operating from the flight deck of the U.S.S. Abraham Lincoln, a Nimitz-class aircraft carrier, before it crashed into the sea about 4:30 p.m. local time on Aug. 31, the Navy said.

Efforts to save the five sailors who were declared missing after the crash ended on Saturday. One person was rescued from the helicopter, according to the Navy, and five people on the flight deck were injured.

The Navy did not elaborate on what had happened to the Seahawk, or what had caused the injuries on the flight deck. But a day after the crash, an item on Page 28 of a regularly published safety report offered more details.

According to the report from the Naval Safety Center, the helicopter touched down on the Lincoln before it “experienced side-to-side vibrations causing main rotor to strike flight deck.” The aircraft then fell over the side of the carrier, the report said. Details of the crash from the safety report were reported by Navy Times.

Matthew Robinson, an aircraft safety expert and former aircraft accident investigator with the Naval Safety Center, said the crash could have been caused — or exacerbated — by any number of factors including mechanical failures, poor maintenance, pilot error, the movement of the aircraft carrier in the ocean, and even wind conditions.

“We need to be cautious about developing theories before evidence collection and analysis,” he said.

The safety report, he said, seemed to show some indication of “ground resonance,” a phenomenon caused in part by an imbalance within the rotor system that can cause helicopters to shudder while on the ground, sometimes violently enough to tear the aircraft apart.

Mr. Robinson said that the Seahawk might have also experienced a dynamic rollover — when a helicopter banks so steeply that it cannot recover equilibrium — and added that blade damage from the rotor’s collision with the deck could have made stabilization impossible.

Five search helicopters joined the U.S.S. Lincoln, the U.S.S. Cincinnati and Coast Guard vessels in the search for the missing sailors, who were part of the Navy’s Third Fleet. They were declared dead on Saturday after a search that the Navy said lasted more than 72 hours. No remains have been found.

The helicopter had been conducting “routine flight operations” about 60 nautical miles off the coast, Navy officials said. On Wednesday, a spokesman for the Third Fleet said that the Navy had nothing to add to the report, and said that the episode was still under investigation.

Navy officials on Sunday identified the sailors as Lt. Bradley A. Foster, 29, a pilot from Oakhurst, Calif.; Lt. Paul R. Fridley, 28, a pilot from Annandale, Va.; James P. Buriak, 31, a second-class Naval aircrewman from Salem, Va.; Sarah F. Burns, 31, a second-class hospital corpsman from Severna Park, Md.; and Bailey J. Tucker, 21, a third-class hospital corpsman from St. Louis.

The MH-60S is a model that has been in use since 2002, according to the Naval Air Systems Command. The 14,000-pound helicopter has a range of 245 nautical miles and can reach a top speed of 180 knots, according to the command. The Navy has more than 250 MH-60S helicopters in use, the command said.

MH-60S helicopters are used for an array of purposes, including “vertical replenishment, combat search and rescue, special warfare support and airborne mine countermeasures” according to Naval Technology, a website that reports on military equipment.