Considerations in relation to Appendix 5 to AMC 20-20 Guidelines for the development of a SB review and mandatory modification programme – Ref ED Decision 2007/019/R

SofemaOnline (SOL) www.sofemaonline.com takes a look at the activities of the Structural Task Group (STG)

Introduction

The TCH should update periodically a list of SB which were already selected for a review with all decisions made, and add to this list all new and revised SB. Moreover, some specific modification SB not linked to an inspection SB may also be selected for review.

Operators information input should be collected and analyzed by the TCH for the STG meeting.

The operators and the Agency should be advised by the TCH of the SB selection list and provided the opportunity to submit additional SB. For this purpose, the TCH should give the operators enough information in advance typically 2 months, for them to be able to properly consider the proposed selection and to gather data.

When an SB is selected, it is recommended to select also, in the same package, inspection SB that interacts with it and all related modification SB.

The main criteria for selecting SBs are defined in the following sub-paragraphs.

• High probability that structural cracking exists
• Related to the number and type of finding in service and from fatigue testing.

A “no finding” result should be associated with the number of performed inspections.

The type of finding should include an analysis of its criticality.

Potential Structural Airworthiness Concern

The structural airworthiness of the aircraft is dependent on repeat inspections to verify the structural condition and therefore on inspection reliability.

A short repeat inspection interval (e.g. short time to grow from detectable crack to a critical length divided by a factor) will lead to increased workload for inspectors and possible increased risk of missing damage.

Special attention should be paid to any single inspection tasks involving multiple repeat actions needed to verify the structural condition that may increase the risk of missing damage (e.g. lap splice inspections).

• Damage is Difficult to Detect During Regular Maintenance
• The areas to inspect are difficult to access;
• NDI methods are unsuitable;
• Human factors associated with the inspection technique are so adverse that crack detection may not be sufficiently dependable to assure safety.
• There is adjacent structural damage or the potential for it

Particular attention should be paid to areas susceptible to Widespread Fatigue Damage (WFD) and also to the potential interaction between corrosion and fatigue cracking e.g. between fastener damage (due to stress corrosion or other factors) and fatigue cracking.

It is recommended to consider the potential interaction of modifications or repairs usually implemented in the concerned areas to check whether the inspections are still reliable or not (operators input)

SB Review and Recommendations

The STG should collectively review the ratings against each criteria to come to a consensus recommendation.

Such a STG recommendation for a selected SB shall consider the following options:

• To mandate a structural modification at a given threshold
• To mandate selected inspection SB
• To revise modification or repair actions
• To revise other SB in the same area concerned by damages
• To review inspection method and related inspection intervals
• To review ALI/MRB or other maintenance instructions
• To defer the review to the next STG and request operators reports on findings for a specific SB or request an inspection sampling on the oldest aircraft

STG recommendations for mandatory action are the responsibility of the TCH to forward to the Agency for appropriate action. Other STG recommendations are information provided to the STG members. It is their own responsibility to carry them out within the appropriate framework.

How Important is Aircraft Inspection Competence in an EASA Part 145 Maintenance Organisation?

At Sofema Online (SOL) www.sofemaonline.com we believe it is extremely important

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