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SAN DIEGO (CNS) — A lawsuit filed on behalf of the families of four Miramar-based Marines killed in a 2018 helicopter crash in Imperial County alleges two companies that manufacture and supply helicopter components are responsible for a defective part that was instrumental to the fatal wreck.

The lawsuit filed in Pennsylvania state court alleges the root cause of the April 3, 2018, crash during a flight exercise near El Centro was the failure of a component part manufactured, sold and supplied by Kampi Components Co. and Diamond Rubber Products Co.

Representatives of the companies could not immediately be reached for comment.

Killed in the crash were Capt. Samuel A. Schultz, 28, of Huntingdon Valley, Pennsylvania, 1st Lt. Samuel D. Phillips, 27, of Pinehurst, North Carolina, both of whom were pilots; and crew chiefs Lance Cpl. Taylor J. Conrad, 24, of Baton Rouge, Louisiana, and Gunnery Sgt. Derik Holley, 33 of Dayton, Ohio.

The complaint filed last week alleges that the crash was caused by the failure of a bypass valve button on the CH-53E Super Stallion heavy-lift helicopter they were riding in, causing “what is known as a ‘hydraulic lock’ condition, resulting in a loss of flight control of the subject helicopter. When this condition occurs, the pilots can do nothing to bring the subject helicopter back under control and are blameless in this crash.”

San Diego-based attorney David S. Casey Jr., who is representing Holley and Conrad’s families, said the bypass valve button utilized rubber that decomposes when exposed to hydraulic fluid.

“Disintegrating rubber in the valve button caused a dangerous blockage in the helicopter’s hydraulic system — making the flight control system uncontrollable and inoperable,” Casey alleged. “There was nothing the pilots could have done to prevent this deadly accident.”

The lawsuit alleges strict liability, negligence and breach of warranty, with the families seeking compensatory and punitive damages.