INOP meaning in aviation

Where this term is used / What it means in practice

INOP appears in technical logs, deferred defect records, MEL/CDL assessments, troubleshooting write-ups, and line maintenance handovers. It describes operational status, not root cause. A component can be marked INOP because it has failed, because it has been intentionally deactivated under approved procedures, or because maintenance has isolated it pending rectification.

In practice, INOP starts a control process. The defect must be recorded, assessed against maintenance data and operational limitations, and either rectified before further flight or managed under approved dispatch relief. For commercial operations, the operator and continuing airworthiness functions must ensure the defect status, rectification interval, placarding, maintenance action, and release to service are all aligned.

What EASA says

Part-M requires continuing airworthiness to be ensured through rectification of defects and damage affecting safe operation, while taking the MEL and configuration deviation list into account when they exist. It also requires all maintenance to follow the approved maintenance programme and maintenance data. For CAMO-managed aircraft, the CAMO is responsible for ensuring the required maintenance is ordered, supervised, and properly released.

Common confusion / Common mistakes

INOP does not automatically mean the aircraft is grounded. Some INOP items may be dispatchable if the operator's MEL permits dispatch under stated conditions and within the applicable rectification interval. The decision is not made by the shorthand itself. It is made by the approved operational and maintenance framework.

Another common error is treating INOP as identical to a deferred defect. INOP is the equipment status. A deferred defect is the controlled maintenance and operational decision to postpone rectification within approved limits. The technical log entry, MEL item, placard, maintenance action, and release status must all line up.