Airworthiness Records (Part VI): Deferred Defect Status

The status of deferred defects is a key element for controlling known aircraft unserviceabilities that are intentionally not rectified immediately. It provides visibility of all outstanding defects that remain open under approved deferral conditions and is essential during audits, airworthiness reviews, aircraft transitions, and operational control.

Defect management systems ensure that faults, malfunctions, and other occurrences affecting or potentially affecting continuing airworthiness are properly captured, assessed, and recorded. These systems may interface with Minimum Equipment List (MEL) provisions, Configuration Deviation List (CDL) allowances, and manufacturer-defined limits.

At any point in time, the deferred defect status shall ensure traceability of all outstanding defects, including their deferral basis and applicable rectification limitations.

Applicability and Scope

Defects are findings that indicate a deviation from the intended condition of the aircraft or its components. Any defect that is assessed as having a serious impact on flight safety must rectified before further flight and cannot be deferred.

For the purpose of continuing airworthiness records, deferred defects include:

• Defects deferred under MEL provisions, which define the conditions under which an aircraft may be operated with specific equipment inoperative, subject to operational limitations and rectification timeframes.

• Defects deferred under CDL provisions, which define acceptable external or structural configuration deviations that do not adversely affect airworthiness, subject to applicable limitations.

• Defects within approved limits and deferred in accordance with approved maintenance data (e.g. AMM, SRM).

Structural damages within approved limits are better managed through the repair status, where they are no longer treated as deferred defects but as recorded structural conditions under approved repair data.

Deferred defect status may also be used to record non-airworthiness defects, including certain cabin-related items, where they are controlled under approved deferral processes.

Recording Deferred Defect Status

Each deferred defect entry typically includes:

• Reference number

• Applicability (aircraft, engine, propeller, or component, including serial number)

• Description of the defect (clear technical description)

• Reference to the source of detection (e.g. work package, work order, or technical log entry)

• Applicable deferral basis and category (e.g. MEL item, CDL, approved maintenance data)

• Deferral date and responsible certifying personnel

• Required rectification limit

• Repetitive interval or threshold (where applicable)

• Rectification status (e.g. open, terminated/closed)

• Details of the rectification

• Date of Certificate of Release to Service (CRS)

• Reference to associated work package, work order, or technical log entry

Special Considerations

Traceability and Continuity

Deferred defects must maintain continuous traceability from the moment of detection until rectification. This includes preserving the original defect record even when transferred across maintenance events or operational periods.

Operational Status Impact

Where applicable, deferred defects may result in operational limitations when controlled under MEL provisions, including potential impact on dispatch criteria, e.g. ETOPS. These limitations must be clearly reflected in the aircraft’s operational documentation and remain in effect until the defect is rectified or the deferral is closed in accordance with approved procedures.

Cumulative Defect Effect Assessment

When deferring or carrying forward defects, the potential hazards arising from the cumulative effect of multiple deferred items on the same aircraft should be assessed. This includes consideration of any operational limitations imposed by the MEL, as well as the combined impact of all outstanding defects on aircraft dispatch, operational capability, and compliance with approved operating conditions.

Conclusion

The deferred defect status provides a controlled and traceable record of all outstanding aircraft defects managed under approved deferral systems.

By linking each defect to its origin, deferral basis, and required rectification conditions, the status ensures continuous visibility of aircraft technical condition and supports compliance with continuing airworthiness requirements.