series-parallel circuit (electrical circuit). A type of electrical circuit in which some of the components are connected in series, and others are connected in parallel.

series resonant circuit. A resonant AC electrical circuit that contains a capacitor and an inductor connected in series. At the resonant frequency of the circuit, the inductive reactance and the capacitive reactance are the same. But they are 180° out of phase, and they cancel each other.
The only opposition to the flow of AC in a series resonant circuit is caused by the circuit resistance.

series-wound generator (electrical generator). A form of electrical generator in which the field coils are connected in series with the armature. Series-wound generators are not commonly used to supply power for aircraft electrical systems because of the difficulty in controlling the output voltage.

series-wound motor (electric motor). A commutator-type electric motor that has the field coils connected in series with the armature. A series-wound motor has a high starting torque, but if it is not operated with a mechanical load connected to it, it will accelerate to a speed that will destroy it. Starter motors for both reciprocating engines and gas turbine engines are series-wound.
serviceable (physical condition). The condition of a piece of equipment that allows it to be returned to service or to be installed in an operating aircraft.
serviceable limits. One type of limits included in a reciprocating engine overhaul manual. If a part measures outside of the new-parts limits, but within the serviceable limits, it will likely not wear to the point of causing engine failure within the next TBO interval.
service bulletin (maintenance information). A bulletin issued by the manufacturer of an aircraft, engine, or component that describes a service procedure the manufacturer recommends to make the device safer or to improve its service life.
service ceiling (aircraft performance). The highest altitude at which an aircraft can maintain a steady rate of climb of 100 feet per minute.
service life. The length of time a piece of equipment can reasonably be expected to operate in a satisfactory manner.
service manual (maintenance information). A manual written by the manufacturer of an aircraft, engine, or component that describes the way the device should be serviced and maintained. The service manual for an FAA-certificated aircraft is approved by the FAA, and it serves as approved data for making repairs.