The Role of Aircraft Defect Management in Continuing Airworthiness

Ensuring the continuing airworthiness of an aircraft and the serviceability of its systems and emergency equipment is critical for safe flight operations. This responsibility includes the rectification of any defect or damage affecting safe operation, strictly in accordance with applicable maintenance data.

Defect Identification and Rectification Priorities

Any aircraft defect that hazards seriously the flight safety shall be rectified before further flight. The decision to determine if a defect hazards seriously flight safety—and thus requires immediate rectification before flight or can be deferred—is made only by authorized certifying staff using approved maintenance data.

If a defect is not rectified before flight, it must be recorded in the aircraft continuing airworthiness record system or, if applicable, the aircraft technical log system.

⚠️ Don’t be misled by the image illustrating this article — the aircraft pictured suffered severe hailstorm damage and would not qualify as a deferred defect. This type of damage must be assessed and repaired in accordance with approved maintenance data before further flight. But not all defects are visible or structural; some may be internal system faults, wear, or minor malfunctions.

Recording and Communication of Deferred Defects

A deferred defect is an identified aircraft defect which has been assessed as being within the requirements of the Minimum Equipment List (MEL), Configuration Deviation List (CDL), or other approved maintenance data, and has had rectification deferred within a specified limit. Sometimes referred to as an Acceptable Deferred Defect (ADD) or a Carried Forward Defect (CFD). It is essential that all deferred defects be communicated to the pilot or flight crew whenever possible prior to their arrival at the aircraft.

Note: The pilot-in-command is ultimately responsible for the decision to operate the flight, even if the aircraft has been certified as airworthy. However, they cannot override airworthiness requirements or authorize the deferral of a defect that exceeds MEL or CDL limits.

Deferred defects should be transferred on to worksheets at the next appropriate maintenance check, and any deferred defect which is not rectified during the maintenance check, should be re-entered on to a new deferred defect record sheet.

Necessary components or parts for rectification should be made available or ordered on a priority basis and fitted at the earliest opportunity.

Note: The Maintenance Control Center (MCC) is usually responsible for coordinating the management of deferred defects by ensuring accurate communication between maintenance teams and flight crews. It monitors defects, oversees the ordering and availability of necessary parts, and schedules rectification activities to minimize operational impact— warm thanks to all of them for making every flight possible.

Use of Maintenance Data and Defect Management

Personnel maintaining the aircraft shall have access to and use only applicable current maintenance data when performing maintenance, including modifications and repairs.

When deferring or carrying forward defect rectification, the cumulative effect of multiple deferred or carried forward defects must be considered, along with any restrictions in the MEL or appropiate maintenance data.

Continuous monitoring of repetitive incidents and defects occurring in flight, as well as those found during maintenance, is crucial. This monitoring should highlight any repetitive defects, and deferred or carried forward defects must be tracked closely.

Aircraft Records and Technical Log System

The aircraft continuing airworthiness records shall include deferred defect rectification details.

The aircraft technical log system should contain all deferred defects that affect or may affect safe operation and should be known to the aircraft commander. The following information should be recorded for each deferred defect:

• Cross-reference for each deferred defect to its original record

• The original date of the defect

• Brief details of the defect

• Details of the eventual rectification and its certification reference, or a clear cross-reference to documentation containing this information

All recorded defects should be reviewed, considering their possible effects on both normal and standby functions of components removed due to the defect.

Reliability Program and Defect Analysis

A Reliability Program should be established with clearly defined procedures for analysis and interpretation of information. This program should enable measurement of the performance of controlled items and facilitate recognition, diagnosis, and recording of significant problems. Such a process allows critical assessment of the program’s overall effectiveness, including the evaluation of repetitive defects.

Defect Management Systems and MEL Application

A documented defect management system is essential to capture information on faults, malfunctions, defects, and other occurrences that may adversely affect continuing airworthiness. This system may include, among others, the Minimum Equipment List system, the Configuration Deviation List system, and deferred defects management.

The MEL allows operating crews to decide whether to accept operations with deferred defects according to its provisions. Personnel involved in continuing airworthiness and maintenance must be familiar with the MEL application procedure to ensure effective communication with the crew when defect rectification is deferred.

Troubleshooting and Root Cause Analysis

Troubleshooting consists of procedures and actions, using approved maintenance data, to identify the root cause of defects or malfunctions. This may include the use of Built-In Test Equipment (BITE) or external test devices.

An assessment of both the cause and any potentially hazardous effect of any defect or combination of defects should be performed to initiate necessary further investigation and analysis. There are a variety of analytical techniques and tools to perform a Reliability Root Cause Analysis.

Conclusion

Together, these practices form the backbone of a robust defect management system that upholds continuing airworthiness and ensures safe operations.

The Reliability Program and Reliability Root Cause Analysis are covered in detail in our Aircraft Maintenance Programs course. If you're interested in deepening your understanding, we invite you to explore it.

For those looking to strengthen their skills in conventional root cause analysis tools—such as the Five Whys and the Cause and Effect Diagram (Fishbone Diagram), which also support reliability investigations—take a look at our course on Problem Solving & Root Cause Analysis.

In an upcoming article, we will delve deeper into the Reliability Program and its role in tracking performance and preventing recurring issues. Stay tuned.