Grampaw Pettibone

Gramps from Yesteryear:

September-October 2000

Illustration by Ted Wilbur

Lava Lament

A CH-53D Sea Stallion with a full load of troops on board was conducting insertion missions from an Army airfield to a landing zone in a lava field 6,560 feet above mean sea level. The pilot and copilot conducted hover power checks before departing the airfield. Winds at departure were 300 degrees at 10 knots, gusting to 15. The helo proceeded to the landing zone, dropped off the troops, returned to the airfield, took on another load and returned to the lava field.

On final approach, the copilot, who was at the controls, began a descent rate to establish the aircraft on glide slope for landing. Both the pilot and copilot were unaware they were experiencing a tailwind. The copilot slid the Sea Stallion to the left to avoid ground support vehicles located along the approach path.

The combined effects of being slow, with a tailwind, in an environment of high density altitude, and in a high gross weight configuration, placed the CH-53D in a hover-out-of-ground effect situation without sufficient power. The induced rate of descent exacerbated the situation, and the CH-53D began dropping to the ground uncontrollably. This is sometimes called “settling without power.”

Realizing the severity of the helo’s condition, the pilot (aircraft commander) pushed both speed control levers full forward in an attempt to increase power. The crew chief called for power and the aerial observer called for a waveoff. The collective was already at its upper limits as the pilot took over the controls. He tried to regain control by pushing the nose over and lowered the collective to execute a waveoff.

Instead, the helo struck the lava field short of the landing zone with little forward airspeed or vertical velocity. The tail rotor and left main mount struck lava rock. Simultaneously, the tail skid lodged in the lava rock causing it to fail aft. The tail rotor blades disintegrated on impact. The tail pylon separated from the aircraft, which then lifted 10 feet off the ground and began rotating counterclockwise.

The Sea Stallion struck the ground a second time and rolled nearly inverted. The engines continued to drive the main gear box and rotor head throughout the sequence, arcing the fuselage around until all the blades were completely sheared off from the rotor head.

Fortunately, this helo was equipped with three-point-restraint troop seats, and vertical deceleration forces were not sufficient to dislodge the seats. As a result, none of the crew and passengers sustained serious injuries.

Grampaw Pettibone says …

What a carousel ride that musta been! I’ll bet more than one heart leapt from chest to throat during that spin-around atop the lava field. The helo was flying at 30 to 40 knots at 100 feet above the ground on the approach. These numbers are consistent with a Sea Stallion when its hitting its Naval Air Training and Operating Procedures Standardization-prescribed parameters. Technically, it was the aerodynamic limitation imposed by the tailwind that did in the CH-53D. The pilots failed to determine the wind direction. Had they done so, they could have adjusted approach direction and stayed within the proper flight envelope. Situational awareness went by the board at a perilous moment.