extended over-water operation. 14 CFR Part 1:
“(1) With respect to aircraft other than helicopters, an operation over water at a horizontal distance of more than 50 nautical miles from the nearest shoreline; and
(2) With respect to helicopters, an operation over water at a horizontal distance of more than 50 nautical miles from the nearest shoreline and more than 50 nautical miles from an offshore heliport structure.”
extension lines (mechanical drawing). Thin lines on an aircraft drawing that extend out from an object to show the location from which dimensions are taken. Dimension lines show the distance between the extension lines.

exterior angle. The angle between one side of a polygon and an extension to an adjacent side. The sum of the exterior angles of any polygon regardless of the number of sides, is always 360°.

external combustion engine. A form of heat engine in which the fuel is burned to release its heat energy outside the engine. A steam engine is a form of external combustion engine. Fuel is burned outside the engine to heat water and change it into steam. The steam is then fed into the cylinder or through the turbine of the engine where it expands and performs work.
external load. A load carried by a helicopter outside of the aircraft itself. External loads are normally carried by slings suspended below the helicopter. 14 CFR Part 1: “A load that is carried, or extends, outside the aircraft fuselage.”
external-load attaching. 14 CFR Part 1: “The structural components used to attach an external load to an aircraft, including external-load containers, the backup structure at the attachment points, and any quick-release device used to jettison the external load.”
external tooth lock washer. A form of thin, spring-steel lock washer. The inside of the washer fits around the bolt or screw, and the outside is notched to form teeth, each of which is twisted.