EASA Part 26 considers the Drivers for Damage Tolerance Evaluations (DTE) and associated Damage Tolerance Based Inspections (DTI)
Sofema Aviation Services (SAS) www.sassofia.com considers the need and regulatory drivers and understand why are required for existing repairs and changes.
Introduction
What is the rationale for DTE and DTI of repairs and changes?
Essentially it is related to the possibility of Early Fatigue or Fails safe requirements (pre 25 571 Amdt 45) which did not necessarily provide for timely inspection of critical structure so that damaged or failed components could be dependably identified and repaired or replaced before a hazardous condition developed.
Repairs and changes can have an adverse effect on the fatigue and damage tolerance of the baseline structure of an aircraft by affecting fatigue cracking behaviour and the effectiveness of existing inspections.
Supplemental Structural Inspection Document (SSIDs) generally only addressed baseline structure. Moreover, it is known that the application of later fatigue and damage tolerance requirements to repairs and even some changes were not always fully implemented according to the relevant certification bases.
The Damage Tolerance Evaluations of repairs and changes is therefore required to maintain the level of safety intended by the implementation of SSIDs and Airworthiness Limitation Section (ALS) applicable to baseline structure.
Concerning Fatigue Cracking During Continuous Operation
Service experience has demonstrated that there is a need to have continuing updated knowledge concerning the structural integrity of aircraft, especially as they become older. Although damage tolerance based inspections are the state of the art for setting up an effective maintenance programme to ensure continued safe operation, they are only reliable if the assumptions on which they are based remain valid.
» A process is required to be developed by TCHs that ensures the continued structural integrity and precludes unsafe levels of fatigue cracking
» To ensure the programme remains valid and mandatory changes are implemented in cases where inspection alone is not reliable enough.
26.301 Compliance Plan for (R)TC holders - Regulation (EU) 2020/1159 (applicable from 26.2.2021)
A holder of a type certificate (TC) or a restricted TC for a turbine-powered large aeroplane certified on or after 1 January 1958, for which the application for TC was submitted before 1 January 2019, shall:
» Establish a compliance plan for continuing structural integrity that describes the planned demonstration of compliance with the requirements set out in points 26.302 to 26.309;
» Submit the compliance plan for continuing structural integrity referred in paragraph (i) to the Agency before 27 May 2021 for approval.
» An applicant for a TC or restricted TC referred to in letter (c) of Article 1 paragraph 2 shall:
» Establish a compliance plan for continuing structural integrity that describes the planned demonstration of compliance with the requirements set out in points 26.303 to 26.306;
» Submit the compliance plan for continuing structural integrity referred to in paragraph (i) to the Agency before 27 May 2021 or, before the issuance of the certificate, if it occurs later, for approval.
26.302 Fatigue and damage tolerance evaluation Regulation (EU) 2020/1159 (applicable from 26.2.2021)
26.303 Limit of Validity - Regulation (EU) 2020/1159 (applicable from 26.2.2021)
26.304 Corrosion prevention and control programme Regulation (EU) 2020/1159 (applicable from 26.2.2021)
26.305 Validity of the continuing structural integrity programme - Regulation (EU) 2020/1159 (applicable from 26.2.2021)
26.306 Fatigue critical baseline structure - Regulation (EU) 2020/1159 (applicable from 26.2.2021)
26.307 Damage tolerance data for existing changes to fatigue-critical structure - Regulation (EU) 2020/1159 (applicable from 26.2.2021)
26.308 Damage tolerance data for existing repairs to fatigue-critical structure - Regulation (EU) 2020/1159 (applicable from 26.2.2021)
26.309 Repair evaluation guidelines - Regulation (EU) 2020/1159 (applicable from 26.2.2021)
Next Steps
Sofema Aviation Services www.sassofia.com & Sofema Online www.sofemaonline.com provides EASA regulatory compliant and vocational training including related to CAMO, AMC20-20 and Part 26/CS 26 please see the websites or email team@sassofia.com
