(2)
Class B rotorcraft-load combination means one in which the external load is jettisonable and is lifted free of land or water during the rotorcraft operation.

(3)
Class C rotorcraft-load combination means one in which the external load is jettisonable and remains in contact with land or water during the rotorcraft operation.

(4)
Class D rotorcraft-load combination means one in which the external load is other than a Class A, B, or C and has been specifically approved by the Administrator for that operation.”

round off (mathematics). The mathematical process in which some of the least significant digits of a number are deleted. The rule for rounding off: If the first digit in the discarded part is 5 or greater, increase the lowest digit in the part being saved by one. If the first digit in the discarded part is less than 5, leave the saved part as it is.
route (air traffic control). A defined path, consisting of one or more courses in a horizontal plane, which aircraft traverse over the surface of the earth.
router (metal or woodcutting tool). A wood- or metal-working power tool, used to cut grooves in a surface, or to cut the core from a honeycomb material. A router consists of a high-speed motor spinning a tool whose cutting edges are on its side. A guide is used to control the depth to which the cutting tool can penetrate the material being routed.
route segment. 14 CFR Part 1: “A part of a route. Each end of that part is identified by:
(1)
A continental or insular geographical location; or

(2)
 A point at which a definite radio fix can be established.”

roving (textile materials). A lightly twisted roll or strand of textile material. Fiberglass roving is used in place of fiberglass mat, to reinforce plastic resins molded into certain structural shapes.
RPM (revolutions per minute). A measure of rotational speed. One RPM is one revolution made in one minute.
rubber cement. An adhesive used to fasten sheets of paper together. Rubber cement is made of unvulcanized rubber dissolved in an organic solvent.
rubidium. A soft, silvery-white, reactive, alkali-metal chemical element. Rubidium’s symbol is Rb, its atomic number is 37, and its atomic weight is 85.47. Rubidium ignites spontaneously in air and reacts violently with water. It is used in the manufacture of photocells and electron tubes.
rudder (airplane control surface). The movable control surface mounted on the trailing edge of the vertical fin of an airplane. The rudder is moved by foot-operated pedals in the cockpit, and movement of the rudder rotates the airplane about its vertical axis.
ruddervator (airplane controls). Control surfaces on an airplane that combine the functions of the rudder and the elevators. Ruddervators are the movable surfaces in a V-tail empennage. Moving together, they act as elevators, rotating the airplane about its lateral axis. Moving differentially, they act as the rudder to rotate the airplane about its vertical axis.