Definition
A maintenance approach in which a component or system is kept in service as long as periodic inspections, tests, or measurements show it is still within acceptable limits. The part is removed or repaired only when its actual condition indicates it is no longer airworthy, rather than at a fixed time interval.
Plain English
Instead of replacing a part on a set schedule, you check it regularly and only swap it out when the checks show it is starting to fail or has fallen outside allowed limits.
Context Anchor
Seen in aircraft maintenance programs, inspection requirements, and maintenance records for parts that are kept in service based on their measured condition.
Derivation
The phrase says it directly: maintenance is performed based on the part's condition, found by inspection, rather than on a calendar or hour limit. Knowing this helps separate it from 'hard-time' maintenance, where a part is replaced at a set interval no matter how it looks.
Why Pilots Care
It can extend component life while preserving safety by catching wear through data instead of replacing serviceable parts prematurely.
Analogy
It is like keeping a tire on a car because its tread and pressure are still within limits, not replacing it only because the calendar reached a certain date.
Intuition Check
On-condition does not mean “use it until it fails.” It means “check it regularly and keep it only if it still meets the required standard.”
Example Sentence 1
The cylinders on this engine are maintained on-condition, so they stay in service as long as compression checks and borescope inspections meet the manufacturer's limits.
Example Sentence 2
Oil analysis trending allowed the operator to schedule on-condition maintenance instead of a fixed-time engine overhaul.