This type of excavator operates in general the same as a slackline cableway, except that it uses a bottomless scraper bucket that must convey its load over the ground instead of through the air. Like the slackline cableway, this machine is operated by a two-drum hoist that controls a track cable that spans the working area and a haulage cable that leads to the front of the bucket. Both cables are reeved through sheave blocks attached to a high guyed mast or tower at the head end of the installation. When the bucket comes in with a load and reaches the desired dumping point, a few rotations of the rear drum of the hoist serve to tighten the track cable and lift the bucket off its load; then the brake is 3346 released on the front drum that controls the haulage cable, permitting the empty bucket and carrier to glide back down the inclined track cable.