Aviation glossary · Limits and countersWhat is TSN / CSN?
Time Since New / Cycles Since New
Total hours and cycles accumulated by an aircraft, engine or component since manufacture. A cycle is normally one take-off and landing.
Why it matters
These numbers appear on dozens of screens and documents. When they are typed in more than one place they drift, and the version an auditor sees may not be the one the planner used.
In AerSynx
Counters are derived from the flight timeline and recomputed after every leg, so a correction to a past leg flows through to every figure that depended on it. Flight Log →