Flying is the practice of suspending scenery, lights, or any other equipment on ropes or cables known as lines . To this end, above the stage, at about two to three times the height of the proscenium arch, there is a grid . This is a flat wooden or metal framework supporting a large number of pulley blocks. The lines run over the pulleys, across the grid and, via further pulleys, down towards the fly floor . Here one of two systems is used.

In the case of counterweight flying, in which wire rope cables are used as the lines, they are permanently attached to counterweight cradles in groups of 3 to 5 (varies between theatres). Each of the lines within one of these line sets is permanently attached to a different point on a steel bar which hangs across the stage, parallel to the proscenium arch, opposite the counterweight cradle. Any object to be flown must be attached to one (or more) or these bars. A suitable number of counterweights is then loaded into the cradle(s) in order to offset the weight of the flying piece so attached. If the weight is not exactly matched, the line set is said to be either bar heavy or cradle heavy if the load is heavier or lighter than its counterweight, respectively. The height of the bar (and cradle) is then controlled by moving a rope, the control line , which is also attached to the cradle. The control line passes through a brake block (mounted on the fly rail ) which is used to lock the line set at the desired height. It is safer to fly things cradle heavy, rather than bar heavy, in case the brake should fail.

The alternative system is hemp flying in which hemp ropes are used as lines and tied off on cleats . As in counterweight flying, the lines are grouped into line sets of 3 to 5 lines, with all the lines within a line set usually being tied off together onto the same cleat. Hemp flying offers more flexibility than counterweights, since the lines are not permanently attached to bars. The flying bars can be removed, and the lines used individually or in non standard groups e.g. supporting a bar diagonally across the stage. The system is however limited by the physical strength of the flymen. The lines within a set are known as the short , mid , and long in three line sets (the short is the one which comes down nearest the fly floor). In four line sets, there are two conventions: short , near mid, far mid and long or alternatively extra short , short , long and extra long . ( loc. The former convention is usually used in the A.D.C.). Five line sets are named similarly. Line sets are numbered from the proscenium arch backwards, starting at one. Counterweight and hemp line sets are usually numbered independently ( loc. they are in the A.D.C.), and the spacing between sets is typically between 6 and 12 inches. It should be noted that on stage lighting bars and borders are also numbered in this way but independently --- L.X. bar 3 and line set 3 (also known as bar 3) are almost certainly not the same, nor even near each other. When flying, up and down are referred to as out and in respectively (meaning out of or in to the stage area). Bars may also be requested by the stage crew at certain standard heights: deck , working height (approximately shoulder height), dusting height (only applies to borders, with the bottom of the border just below shoulder height), weighting height (with the bottom of the cloth (etc.) at about four feet above the stage) or grid (as high a possible, or at least out of the way).

Flying is mainly used to suspend on stage lighting, curtains and scenery. Flown pieces of scenery, called flying pieces , are usually suspended from a bar by lengths of flying wire which are attached to the piece with flying irons and grummets . Bottle strainers may be used for fine adjustment of the lengths of the wires. If the exact height of the piece is critical, it must be deaded . If it is flown on a counterweight line set, then this involves marking the point on the control line which is aligned with the dead rail when the piece is at the correct height with a piece of electrical tape ( gaffer tape should not be used). In the case of a hemp line set, the piece is adjusted to slightly higher than is required (to allow for the hemps settling in), carefully levelled by adjusting the lines individually and then tied off. If the piece is slightly too high, the hemps may be stretched a little by bouncing . If it is necessary to live fly the piece ( i.e. move it during a performance), then this knot will be the bottom dead , usually tied off to a cleat on the dead rail (note that dead rail has different meanings in hemp and counterweight flying) and left alone for the rest of the shows run . When the piece is out , it will be tied off again on its usual cleat on the fly rail .