A military aviation mishap board is investigating the cause of Tuesday’s crash of a CH-53D Sea Stallion helicopter which went down on a sandbar in Kaneohe Bay just five minutes after takeoff.

The investigation is still in its preliminary stages, said 2nd Lt. Diann Olson, a spokeswoman for Marine Corps Base Hawaii. A Naval Safety Center investigator and the senior member of board arrived yesterday to work with specialists in aircraft maintenance, operations and safety; and a flight surgeon.

Olson said the Marines will meet with the Coast Guard today to discuss the 500 yard safety zone established to keep people away from the crash scene on the sandbar, which is a favorite recreational spot for boaters to picnic in Kaneohe Bay.

The Coast Guard said the safety zone will be maintained through the weekend. There is now one boat patrolling the area. Boaters with questions can raise the patrol boat on channel 16 on their VHF transmitter.

Marines are also returning today to the crash scene to continue collecting debris from the helicopter, which was built in the 1960s, Olson said.

The Navy’s Mobile Diving and Salvage Unit 1 from Pearl Harbor is working on a plan to remove the wreckage. Options include moving the helicopter to a barge with a crane or to lifting it off the sandbar with another heavy lift helicopter.

Once the wreckage of downed aircraft is moved to shore, investigators will analyze the debris and be able to distinguish between damage from impact or component malfunction and any damage due to the salvage efforts, Olson said..

The helicopter had 1,300 gallons of JP-8 fuel on board when it went down, Marine officials said. Pacific Environmental Corp., the Clean Island Council, the Coast Guard, Marine Corps Base Hawaii’s environmental office, with support from the Department of Land and Natural Resources, extracted about 700 gallons of fuel from the helicopter’s fuel tanks yesterday and monitored the impact area.

Cpl. Jonathan D. Faircloth, 22, who had survived combat tours in Afghanistan and Iraq, was killed in Tuesday’s crash. He was an aerial observer with Marine Heavy Helicopter Squadron 363.

The three HMH-363 crewmen injured in the crash — pilot Maj. Clinton J. Collins, copilot Capt. Kevin F. Hayles, and crew chief Cpl. Ronnie E. Brandafino remain in the Queen’s Medical Center in stable condition.

A memorial service for Faircloth is scheduled at the base chapel April 7.