Recurrent Defect Control – Sofema Aviation Services (SAS) www.sassofia.com looks at the process of managing short-term defects in the context of the organisations reliability system.
Introduction
During the last decades, aircraft technical reliability has continued to improve. Incremental developments are driven by improved technical design, development & service bulletin (SB) driven modifications. Nevertheless, there is one area which continues to dominate the landscape and that is the subject of managing recurring defects.
Repetitive defects are often costly in terms of maintenance and can lead to a loss of customer satisfaction when delays are incurred.
- A key issue is the failure to incorrectly address and rectifies the defect so that it re-occurs within a short period of time.
- Maintenance Control Technical Support Teams often have difficulty tracking and resolving such defects.
The general consensus across MCC & Maintenance provisions is that there is always a possibility to make improvements and small incremental improvements can lead to a measurable bottom-line financial improvement.
Legacy & / or manual systems used to manage repetitive and deferred defects can be time-consuming and lead to underperformance due to errors related to tracking of related defects and ATA codification.
- Note: It can be time-consuming to manually sift through via Excel or other static technology data in hundreds of pages of Pilot Reports (PIREPS).
Concerning repetitive defects, the challenge faced is typically related to the need to:
- Continually track all such defects
- Understand the rate of occurrence
- Rectify correctly
- Monitor the rectification for satisfactory closure
- Consider based on the scalability of occurrence what mitigations are available to improve the reliability
o Service Bulletins
o Upgrade Program
- Multiple MEL discrepancies may combine to lead to additional out of service requirements due to obligation to rectify conflicting defects
- ATA 32 (Wheels & Brakes) is a leading driver of technical delays
How to recognize a shortfall in technical dispatch reliability?
When the data is analyzed a number of generic determinations can be made which are summarized below:
- Insufficient fleet redundancy during the summer operating window (maximum Utilisation)
- Word Wheels & Brakes due to high utilization
- Possibly of structure damaged due to lightning strikes (more prevalent during summer weather conditions)
- Additional delays rolling over from overnight maintenance activities (more maintenance within a short timeframe)
- Errors which are in some way related to Human Factors tend to occur at a higher frequency when there is pressure to deliver an acceptable “On Time Performance (OTP)”
Example of typical defects and occurrence (small fleet) 12 months operations:
- ATA 32 MLG/NLG
o Tyres worn to limits 10 occasions
o Oil leakage found on NLG or MLG 6 occurrences
o Cut found in Tyres 5 occasions
o LGCIU fault 6 occurrences
o Brake block overheat 2 occurrences
o Aircraft reported drifting of aircraft 2 reports
o Landing Gear not down & Locked 2 reports
- ATA 27
o ELAC (PITCH) FAULT” 4 reports
o Flight Control Slat system fault 3 reports
- ATA 36
o ENG 1 or 2 Bleed fault 10 occurrences
o PRV Failure / Problems 4 reports
- ATA 34
o ADIRU fault (IR or ADR) 5 reports
- ATA 73
o ENG drain mast fuel leak 8 occurrences
- ATA 21 Pack
o Pack 1 or 2 Fault 6 occurrences
Developing Improvements & Mitigations
- Introduce additional preventive actions which can be shown to provide an acceptable Return on Investment.
o New Tasks to be developed?
o Increased Periodicity of existing tasks?
- Optimize shift working, introduce improved shifts to align with the aircraft availability (note the challenge where the maintenance personnel is a contract maintenance provider) (Follow HF Principles).
- Consider the feasibility of additional night shift resources to improve the manpower availability when the aircraft is available overnight.
- Optimize short term maintenance planning to ensure the best match for aircraft availability and available manpower. (Requires close co-operation between MCC – Operations & Technical Crews).
o Pay particular attention to the need to ensure a positive motivation and strong culture of support.
Critical assessment of the effectiveness of the maintenance program may involve:
- Comparisons of operational reliability with established or currently understood standards
- Analysis and interpretation of trends
- The continuous evaluation of repetitive defects
- Confidence testing of expected and achieved results
- Studies of component life-bands and survival characteristics
- Reliability predictions
- Additional engineering analysis and interpretation
Improving Component Time-On-Wing
Scheduled removal is usually much lower than the cost of a severe unscheduled breakdown and it is necessary for each individual operator to optimize its own Aircraft Maintenance Program (AMP) and to determine where optimizations can be delivered by considering the introduction of additional tasks or identifying which part numbers should be treated with a soft-time limit.
Typically, airlines use mean time between unscheduled removals (MTBUR) and mean time between failures (MTBF) as metrics for reliability compared to industry or airline historical data.
- Whilst this information is valid an additional metric which can provide a useable indication relates to time-on-wing (TOW). Time-on-wing is either Time Since New (TSN) or Time Since Installation (TSI).
- Component maintenance costs are largely influenced by time-on-wing. In general, the longer a component remains on wing, the lower the life cycle costs of the component with fewer repair cycles in the life of the component.
Note: Maximization of life-usage of a part number on the aircraft doesn’t always lead to optimal costs for the airline, as a failure of a part during operation can lead to additional costs related to out-of-service times or AOG costs.
Next Steps
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Sofema Aviation Services (www.sassofia.com) and Sofema Online (www.sofemaonline.com) offer EASA Regulatory Compliant and Vocational Training across a range of Aviation Areas – please see the following 2-day course to implement your own MCC – Defect Control Process. For additional details please see our websites or email Team@sassofia.com
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Aircraft Maintenance, aviation, Aviation Training, Regulatory training, Online Training, Aircraft Reliability, Reliability Systems, Aircraft Reliability Systems, SAS blogs, Aircraft Maintenance Program (AMP), Aviation MCC, PIREPS, Recurrent Defect Control, On Time Performance (OTP), service bulletin (SB)
