Definition
An inspection performed on a rotating component, such as a propeller hub, crankshaft flange, or wheel, to measure how far it deviates from true rotation about its axis. The part is rotated against a dial indicator, and the total amount of wobble or eccentricity recorded is compared against the manufacturer's allowable limits.
Plain English
A test that checks whether a spinning part runs perfectly true, or whether it wobbles. A measuring tool is held against the part while it is turned, and the amount of wobble is read off and compared to what the manufacturer allows.
Context Anchor
Seen in aircraft maintenance, especially after a propeller strike, unusual vibration, wheel work, or inspection of rotating parts.
Derivation
From 'run out,' meaning to deviate or stray from a true path. In machining, a part that does not rotate cleanly about its axis is said to 'run out' from true. The check measures how much it does so.
Why Pilots Care
Detects imbalance that produces vibration, reduces component life, and can lead to in-flight failure if left uncorrected.
Analogy
A bent bicycle wheel gives a simple picture: as it spins, part of the rim moves side to side instead of staying in one smooth path. A runout check measures that kind of unwanted movement on an aircraft part.
Intuition Check
Runout Check does not mean an engine run-up or a test run of the aircraft. It means measuring whether a rotating part stays true as it turns.
Example Sentence 1
After the prop strike, the mechanic performed a runout check on the crankshaft flange before returning the engine to service.
Example Sentence 2
Excessive crankshaft runout required the engine to be removed for further inspection.