Navy salvage experts will spend the weekend planning how they will remove the wreckage of the 21-ton Sea Stallion helicopter that crashed on a sandbar two miles from Marine Corps Base Hawaii at Kane­ohe Bay.

The investigation into Tuesday’s crash, which killed one Marine and left three others in the hospital in stable condition, is still in its preliminary stages, said Lt. Diann Olson, a spokes­woman for the Marine base.

An aviation mishap board has been convened to investigate the cause of the crash of the CH-53D helicopter, which went down five minutes after takeoff.

A Naval Safety Center investigator and the senior member of the board arrived in Kane­ohe Thursday to work with a flight surgeon and specialists in aircraft maintenance, operations and safety.

The Coast Guard will continue this weekend to enforce a 500-yard safety zone to keep people from the sandbar, a popular recreational spot where boaters picnic.

Another patrol craft will be added to augment the one that has been patrolling the crash area around the clock since the crash occurred. Boaters with questions can contact the patrol boat on Channel 16 on their VHF transmitters.

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

Bill Doughty, Pearl Harbor spokes­man, said, “Salvage of the downed CH-53D will commence only after a thorough plan is in place that considers safety, protection of the environment and integrity of the investigation. All fuel and hydraulic lines have been depressurized, and fluids have been evacuated. We do not anticipate any leakage or spillage when the aircraft is removed.”

Navy divers have placed containment buoys to capture leaking fluids and steel netting to snare large debris. The helicopter had 1,300 gallons of JP-8 fuel on board when it went down.