SAN DIEGO — A brief Navy narrative of a fatal helicopter crash off Southern California says the aircraft experienced “side-to-side” vibrations that caused the main rotor to hit the deck of an aircraft carrier while landing, The San Diego Union-Tribune reported.

The MH-60S Seahawk fell off the deck of the USS Abraham Lincoln on Aug. 31. One crewmember was rescued and five were declared dead after a search. Five sailors on the carrier deck were injured.

The crash summary in a Naval Safety Center document, first reported by the Navy Times, did not include any information on what might have caused the vibrations.

Michael Canders, a retired military helicopter pilot who is the director of the Aviation Center at Farmingdale State College in New York, told the Navy Times that side-to-side vibrations can occur if rotor blades are out of balance.

“All of that has to be carefully balanced to make sure you don’t have these sorts of excessive vibrations,” he said.

Oakhurst Pilot Among the 5 Sailors Killed

The Navy announced on Sept. 4 that the missing crewmembers had been declared dead and that the search efforts were shifting to recovery operations. The helicopter sank about 70 miles off San Diego.

The five sailors who died were identified as Lt. Bradley A. Foster, 29, a pilot from Oakhurst, California; 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, Missouri.

The aircraft belonged to the Navy’s Helicopter Sea Combat Squadron 8. The Union-Tribune reported Tuesday that the squadron’s spouses club has raised almost $180,000 for the families of those who died.