Inquiry Tells Why Marine Helicopter Crashed, Killing 4

The June 1, 1984, crash of a Marine Corps Super Stallion helicopter off San Clemente Island that killed four crew members stemmed from no single cause but came about through a series of seemingly unrelated events, a Marine investigation has concluded.

The accident investigation found that the ultimate responsibility for the crash must be shared by the Marine Corps and Navy, as well as the company that had built a truck that the doomed copter was carrying at the time.

The crash was the first of six major Super Stallion helicopter accidents in which 19 Marines have been killed over a two-year period. But the report declined to attribute the crash to any specific deficiency in the helicopter, a mammoth three-engined aircraft that is the largest helicopter in the free world.

Truck Began to Break Up

A copy of the 500-page report was obtained by The Times. It includes the pilot and aircraft flight logs, maintenance records, statements by witnesses, engineering analyses and photographs of the wreckage.

The crash itself began when a large truck, which was being lifted by the copter from a ship for delivery to combat units ashore, started to break up and severed a part of the cargo sling used to lift it, the report says. The force of the sling snapping sent a shock wave through the helicopter itself, triggering a violent vertical oscillation. The pilots, one of whom was making his first shipboard cargo pickup, attempted to control the oscillation, but that only worsened the situation to the point that the vibrations finally tore the helicopter to pieces in midair, the report concludes.

‘Copter Out of Control’

Several witnesses said the helicopter seemed to disintegrate before it plunged into the Pacific.

“The helicopter went out of control,” said Marine Sgt. Dulles H. Arnette, describing to military investigators the death of his squadron mates and friends.

“It seemed to have rolled to the right with its tail up just higher than the nose. . . . I then saw the helicopter start to come down and what appeared to be brown smoke . . . on the No. 3 engine side.”

“At about that time I screamed, ‘No,’ and watched the smoke around the helicopter and debris in the air as it hit and disappeared in the ocean. Even after the plane was gone parts of it floated out of the sky.”

Arnette, who later made a chilling tape recording in which he said flight personnel were concerned about alleged mechanical problems with the helicopter, died himself last May in the crash of another Super Stallion.

Among the report’s findings:

- When the Marine Corps took steps in 1981 and 1982 to procure the trucks, it did not ensure that they were certified for transport by its helicopters, but instead had relied on an Army analysis, which didn’t take into account the Marine Corps’ specialized lifting requirements.

- Fixtures for attaching cargo slings to the truck, which was manufactured by AM General Corp. of South Bend, Ind., did not meet Marine Corps specifications, even though the company had claimed in late 1982 that they satisfied military strength standards.

- When concerns were first raised about the trucks’ potential deficiencies in 1983, Marine Corps headquarters failed to properly notify subordinate commands about possible restrictions on helicopter lifting of the equipment. A later re-evaluation of the trucks showed they did not meet specifications, but that study was not completed until August, 1984, two months after the crash.

- The Navy Air Systems Command, citing budgetary constraints, rejected a proposal in 1982 by the helicopter’s manufacturer, Sikorsky Aircraft Division of Stratford, Conn., to install a device, a damper, that would have desensitized the controls and helped pilots overcome severe oscillations or bouncing. The device was finally approved in April, 1985.

- The pilots took the wrong actions in an attempt to save their aircraft, perhaps because the portion of the flight manual dealing with such emergencies was “poorly written and ambiguous.”

- Although it was not ruled a causal factor in the crash, the possibility was raised in the report that an electrical circuit failure may have prevented the crew from jettisoning the heavy truck. Such a malfunction, the report says, “may have precluded the operation of a safety system that could have broken the chain of events leading to the catastrophic structural failure of the aircraft.”

In reviewing the events leading up to the accident, the investigation found that nothing unusual had occurred that would give an indication of what was to happen.

Three Super Stallions had been assigned to transport men and equipment from two ships, the New Orleans and the Denver, onto San Clemente Island.

Although the mission was delayed by inclement weather, once under way it had gone off without incident.

Aboard one of the aircraft from the Tustin-based Marine Heavy Helicopter Squadron 465 was Capt. Barry M. Thompson, 28, the pilot; 1st Lt. Thomas O. Shaefer, 25, the co-pilot; Lance Cpl. James M. Kloss, 24, the crew chief, and Cpl. John J. Utsinger, 21, a qualified crew chief who was assigned as first mechanic for this operation.

Thompson had logged 1,719 hours of flight time, including 682 hours in the CH-53E, while Shaefer had flown 389 hours, 92 of which were in the Super Stallion. Both had received high marks during evaluation flights less than three months earlier.

On its first flight, Thompson’s helicopter, No. YJ-05 and code-named Warhorse, had delivered a truck to the beach and on its second run carried 15 troops.

Between those two trips, however, Thompson made an unscheduled landing on the island, possibly to let his crew manually retrieve a cargo hook.

After delivering the troops, and with Shaefer apparently now at the controls, the helicopter returned to the Denver to pick up another truck.

The hookup with the cargo, however, took an unusually long time, according to the shipboard loading crew, because the pilot was having trouble maintaining his position while hovering above the truck, which weighed 11 1/2 tons. According to the Denver’s air operations officer, Thompson had told him Shaefer was making his “first lift ever” from a ship.

Although a portion of the truck’s vertical exhaust pipe was broken off by one of the cargo sling’s four cables, and the truck was dragged a short distance across the deck, it was finally lifted clear of the ship.

Despite those initial problems, there seemed to be no further difficulties as the helicopter climbed up and away from the ship.

But with Warhorse 500 yards off the starboard side of the Denver, at an altitude of about 300 feet and traveling 60 to 80 knots, disaster struck.

“The first thing I noticed upon looking up at the helo was the rear rotor system falling apart and flying off to the left. . . ,” Sgt. Edward Mata Jr., who was on board the ship, told investigators. “The next thing I noticed was the helo cutting the load and then the helo started spinning and falling toward the ocean . . . before it hit the water surface the helo exploded into flames and fell apart upon impact.”

The wreckage sank quickly and rescue crews found no survivors, just a few pieces of debris floating on the surface.

According to the accident report, “The initial failure that ultimately led to the crash” occurred in the bolts that held the bed of the truck to its frame. This was brought on when lifting bars, to which the cargo sling was attached at the back of the truck, deformed under the load and began pinching the bed, lifting it upward.

As the bed peeled up, its sharp metal edges cut through two of the three ropes of the right rear sling and damaged the third, enough that it pulled apart due to the stress on it.

When the final rope snapped, it sent a shock wave up through the sling into the helicopter itself, triggering a violent vertical oscillation, known as “collective bounce,” which the crew apparently tried to overcome through manipulation of the flight controls.

“The normal pilot response to abnormal aircraft vibration is to grab and hold onto the controls,” the accident report stated. “In this instance it was the incorrect response, indicating that the pilot(s) did not realize they were in collective bounce.”

Instead of letting go of the controls as called for in the manual, the crew’s efforts only worsened the situation, according to the investigative report. Soon the helicopter, with the heavy weight of the truck still dangling beneath it, was bouncing much like an elastically tethered paddleball.

The shaking and vibrations finally became so severe the helicopter began to come apart. The tail rotor snapped off, making controlled flight impossible. The main rotor blades stopped turning, causing the rest of the aircraft beneath to spin around to the right two or three times.

Then, a huge main rotor blade slammed into one of the engines, tearing it loose and igniting the fireball that was seen by witnesses just before the helicopter plunged nose-first into the water.