Definition
A flexible rotating shaft that mechanically connects an engine drive point to the tachometer indicator on the instrument panel, transmitting the engine's rotational speed so it can be displayed in RPM.
Plain English
A spinning cable inside a protective sheath that carries the engine's spinning motion up to the RPM gauge so the pilot can see how fast the engine is turning.
Context Anchor
Seen in aircraft engine instrument systems, maintenance discussions, and troubleshooting when the tachometer indication is missing, jumpy, or clearly wrong.
Derivation
From Greek 'tachos' (speed) plus '-meter' (measuring device). The cable is simply the mechanical link that drives the speed-measuring instrument.
Why Pilots Care
A failed cable leaves the pilot without RPM indication, complicating engine management and potentially leading to over- or under-speed operation.
Analogy
Like the old speedometer cable in a classic car: a spinning inner wire inside a flexible housing carries motion from one end to a needle at the other.
Intuition Check
Do not think of this as an electrical cable by default. In this context, a tachometer cable usually means a flexible mechanical cable that physically spins inside its outer casing.
Example Sentence 1
During run-up the tachometer needle began to flutter, and the mechanic later found a worn tachometer cable was the cause.
Example Sentence 2
During the annual inspection the mechanic replaced the tachometer cable to restore accurate engine speed readings.