Aviation glossary · Limits and countersWhat is TSO / CSO?
Time Since Overhaul / Cycles Since Overhaul
Hours and cycles accumulated since a component's last overhaul — the counters that reset when the component is restored to a defined standard.
Why it matters
These reset and life limits do not, and the two are often shown side by side. Treating them as the same kind of number is how a part gets planned against the wrong figure.
In AerSynx
Since-new and since-overhaul counters are held separately and derived from the same timeline, so an overhaul resets what it should and nothing else. Asset Registry →