NASA-LLIS-0937

Abstract

<strong>Description of Driving Event:</strong> <br>A three-man crane operating crew was assisting a three-man crane overhaul crew to refurbish a 140Ton crew and to refurbish a 110-ton government owned mobile crane on September 15, 2000. On this day, the overhaul crew was to install new boom pendants, requiring the cable bridle and its associated cables to be moved from its temporary stowage location behind the cab of the crane to a point on the boom where it could be attached to the boom pendants. To move the bridle with its associated cables forward along the length of the boom, a second 65-ton government owned mobile crane was used to lift the cable bridle assembly and pull it to the new location. The cable bridle (weighing approximately 1100 pounds) was attached to the hook of the 65-ton crane with a web sling (rated for 10,000 pound capacity in the vertical choker configuration) used in a horizontal choker configuration. <br>The crane operating personnel were performing the following duties: One member operated the 65Ton crane used to lift the cable bridle assembly and pull it to its new location. A second member operated the 140-ton crane in order to play out cable while the bridle assembly was being pulled. The third member was on the ground acting as the signalman for the two crane operators. With the three crane operating crew members in position and the overhaul crew members observing the operations, the cable bridle was lifted and slowly pulled along the boom of the 140-ton crane. During this movement the cable bridle underwent several yawing motions due to the cables binding on the sheaves as the cable unspooled from the take-up drums. The sheaves were binding because the cables were being pulled at an angle and the choker hitch configuration did not keep the bridle straight and level with the direction of pull. <br>The web sling failed allowing the bridle to fall. The bridle assembly impacted the butt section of the boom of the 140-ton crane before it landed on the ground. At the same time, the block of the 65-ton crane swung back striking the stowed jib boom attached to the main boom of the 65-ton crane. The jib boom of the 65-ton crane was a total loss because a portion of the main support section was severely damaged beyond repair. The butt section of the boom of the 140-ton crane was slightly bent and the bridle was damaged in several places. The falling cables cracked the overhead glass on the cab of the 140-ton crane.