Review the Following
Details of ageing aircraft system requirements with any specified sampling programmes, (if applicable)
Details of specific structural maintenance programmes, (if applicable), including but not limited to:
a. Damage Tolerance and Supplemental Structural Inspection Programmes (SSID)
SUPPLEMENTAL STRUCTURAL INSPECTION PROGRAMME (SSIP)
Increased utilisation, longer operational lives, and the high safety demands imposed on the current fleet of transport aeroplanes indicate the need for a programme to ensure a high level of structural integrity for all aeroplanes in the transport fleet.
This AMC (20-20) is intended to provide guidance to TCHs and other DAHs to develop or review existing inspection programmes for effectiveness. SSIPs are based on a thorough technical review of the damage-tolerance characteristics of the aircraft structure using the latest techniques and changes in operational usage. They lead to revised or new inspection requirements primarily for structural cracking and replacement or modification of structure where inspection is not practical.
b.SB review performed by the TC holder
The case of an SB for which an AD has been issued, irrespective of whether it is designated by the TC/STC holder as âmandatoryâ, âalertâ or âhighly recommendedâ, is clear: these are part of the Mandatory Continuing Airworthiness Instructions and must be applied in all cases.
The case of SBs designated as âmandatoryâ, âalertâ or âhighly recommendedâ by the TC/STC holder for which no AD has been issued is more complex and the following cases should be considered:
The TC/STC holder subsequently includes such SB (e.g. repetitive inspection instructions) in the manufacturer maintenance programme (Maintenance Review Board Report (MRBR) or Manufacturer Recommended Programme) for the aircraft concerned. In this case, the SB under consideration will need to be included in the aircraft maintenance programme as defined in Commission Regulation (EU) No 1321/2014, M.A.302(d) and (g) (see also AMC M.A.302(d)) to ensure compliance with instructions for continuing airworthiness issued by the TC/STC holder.
The TC/STC holder does not include such SB in the manufacturer maintenance programme (MRBR or Manufacturer Recommended Programme) for the aircraft concerned. In this case, the final decision to apply such SB lies with the owner/operator or contracted CAMO, as M.A.302(g) does not apply.
The TC/STC holder issues an SB defining a modification, the related embodiment instruction and the relevant scheduled maintenance requirements, where these may or may not be subsequently included in the manufacturer maintenance programme (MRBR or Manufacturer Recommended Programme) for the aircraft concerned. In case the SB will not be included in the manufacturer maintenance programme, the final decision to apply it or not lies with the owner/ operator or contracted CAMO. If the final decision is to apply the SB, then the aircraft maintenance programme needs to be updated to include the scheduled maintenance requirements.
Finally, in relation to points 2. and 3. above, for all non-mandatory modifications and/or inspections, including SBs classified by the TC/STC holder as âmandatoryâ, âalertâ or âhighly recommendedâ and not covered by a corresponding AD, for all large aircraft, or aircraft used in commercial air transport, an embodiment policy is to be established, as required by M.A.301(7.). That policy should then result in a substantiated (and recorded) operatorâs decision for each SB to apply it, or not.
c. Corrosion Prevention and Control
The operatorâs continuous analysis and surveillance system should contain procedures to review corrosion inspection task findings and establish corrosion levels. These procedures should provide criteria for determining if findings that exceed allowable limits are an isolated incident not typical of the operatorâs fleet. The operatorâs programme should also provide for notifying the competent authority
Whenever a determination of Level 2 or Level 3 corrosion is made. Due to the potential urgent airworthiness concern associated with a Level 3 finding, the operatorâs procedures should provide for notification as soon as possible but not later than 3 calendar days after the Level 3 determination has been made.
d.Repair Assessment
Where repair evaluation guidelines, repair assessment programmes or similar documents have been published by the TCH they should be incorporated into the aircraftâs maintenance programme according to Part-M requirements.
This fatigue and damage-tolerance evaluation of repairs will establish an appropriate inspection programme or a replacement schedule if the necessary inspection programme is too demanding or not possible. See AMC 20-20 Appdx 3
e.Widespread Fatigue Damage
The likelihood of the occurrence of fatigue damage in an aircraftâs structure increases with aircraft usage. The design process generally establishes a design service goal (DSG) in terms of flight cycles/hours for the airframe. It is generally expected that any cracking that occurs on an aircraft operated up to the DSG will occur in isolation (i.e., local cracking), originating from a single source, such as a random manufacturing flaw (e.g., a mis-drilled fastener hole) or a localised design detail. It is considered unlikely that cracks from manufacturing flaws or localised design issues will interact strongly as they grow. (Widespread Fatigue Damage EFD)
f.Limit of Validity
Limit of validity (LOV) is the period of time, expressed in appropriate units (e.g. flight cycles) for which it has been shown that the established inspections and replacement times will be sufficient to allow safe operation and in particular to preclude development of widespread fatigue damage. The LOV should be based on fatigue test evidence.
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Aircraft Maintenance Program, Review of Critical Items Part 2
