In aviation the term “INOP”, short for “inoperative”, refers to an item of aircraft equipment or a system that is partially or totally unavailable to the pilot or crew.
How do pilots know a system is INOP/Inoperative?
Pilots will most often come across the term INOP in the aircraft technical logbook (“tech log”) which is an official and up to date record of the status of the aircraft. The tech log is reviewed prior to each flight before being signed off as legally acceptable by the captain.
The crew will first check the “Deferred Defect” section of the tech log which will indicate if the aircraft is operating with any MEL items. The Minimum Equipment List (MEL) may be used to allow the aircraft to dispatch with an INOP system or component.
More about how the MEL allows dispatch with inoperative items can be found here: Minimum Equipment List (MEL).
Any items marked as “INOP” on the previous flight will require maintenance action – either to reinstate the inoperative system, or to allow legal dispatch in accordance with the MEL.
How do Pilots Record Inoperative Systems in the Tech Log?
During the flight any system that does not work or fails during flight will be recorded as INOP in the tech log by the crew. This record will include as much detail as possible about what happened with the relevant system or instrument. On arrival at the gate the aircraft will be met by engineers/mechanics who are responsible for rectifying the defect prior to the next flight. In some circumstances, if the defect can’t be repaired, the aircraft may be allowed to dispatch in accordance with the Minimum Equipment List. Learn more about the Minimum Equipment List(MEL) here.
FAA Regulation FAR 91.213 – Inoperative Instruments and Equipment
FAA Regulations FAR 91.213 (excerpt) states: “…no person may take off an aircraft with inoperative instruments or equipment installed unless the following conditions are met:
1. An approved Minimum Equipment List (MEL) exists
3. The approved Minimum Equipment List must…(ii) provide for the operation of the aircraft with the instruments and equipment in an inoperable condition.
4. The aircraft records available to the pilot must include an entry describing the inoperable instruments and equipment.
5. The aircraft is operated under all applicable conditions and limitations contained in the Minimum Equipment List…
The full FAR (FAA Regulation) is available here: https://www.govinfo.gov/content/pkg/CFR-2010-title14-vol2/pdf/CFR-2010-title14-vol2-sec91-213.pdf.
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