Rope team may be used in the event of a crevasse accident, e.g. to make a Swiss pulley in order to rescue a fallen climber. For larger groups of about four people or more, recovering a fallen man is most easily done using a team pull. When "walking on a rope", the fall of one person - for example, into a crevasse - must be broken by the rest of the rope team members. So there is a danger that such a fall can endanger the entire team. On steep firn or ice-covered mountainsides, where possible and appropriate, the rope must be
Block and tackle more precise estimate of efficiency is possible by use of the sheave friction factor, formula_12 (which may be obtainable from the manufacturer or published tables). The relevant equation is: Typical formula_12 values are 1.04 for roller bearing sheaves and 1.09 for plain bearing sheaves (with wire rope). The increased force produced by a tackle is offset by both the increased length of rope needed and the friction in the system. In order to raise a block and tackle with a mechanical advantage of 6 a distance of 1 metre, it is necessary to pull 6 metres of rope through the