Appendix 2
d. Maintenance Actions.
(1) For all areas that have been identified as susceptible to WFD, the current maintenance program should be evaluated to determine if adequate structural maintenance and inspection programs exist to safeguard the structure against unanticipated cracking or other structural degradation. The evaluation of these inspections should typically be done as follows:
(a) Determine the level (inspection threshold, repeat interval, and methods) of the inspection for each susceptible area that is necessary to maintain the required level of safety.
(b) Review the existing maintenance programs to determine if they provide the required level of safety.
(2) For airplanes approaching the estimated occurrence of WFD, a program should be developed and recommended to the FAA that provides for replacement or modification of the susceptible structural area.
e. Period of Evaluation Validity. The initial evaluation of the complete airframe should cover a significant forward projection of airplane usage beyond the design service goal. Typically an assessment through at least an additional twenty-five percent of the design service goal would provide a realistic forecast with reasonable planning time for necessary maintenance action. However, it may be appropriate to vary the evaluation validity period depending on issues such as:
(1) The projected useful life of the airplane at the time of the initial evaluation (could increase or decrease the validity period).
(2) Expectations of improved Non Destructive Inspection (NDI) technology (could decrease the initial validity period, pending new methods becoming available).
(3) Airline advance planning requirements for introduction of new maintenance and modification programs.
(4) Providing sufficient forward projection to identify all likely maintenance/modification actions essentially as one package.
Subsequent evaluations should follow similar validity period guidelines as the initial evaluation.
3. DOCUMENTATION.
a. The manufacturers should revise the SID as necessary and/or prepare Service Bulletins that contain the recommendations for inspection procedures and replacement or modification of parts or components necessary to preclude Widespread Fatigue Damage. Since WFD is applicable to all operators and is a safety concern for older airplanes, identified inspection or modification programs will be made mandatory. In addition, any service bulletins or other service information
Appendix 2 publications revised or issued as a result of in-service WFD findings resulting from implementation of these programs may require separate AD action.
b. If the manufacturer chooses not to update the SID or prepare Service Bulletins, it should develop a WFD document containing recommendations for inspection procedures and replacement or modification of parts or components necessary to preclude WFD. The document should be prefaced by the following:
(1) Identification of the variants of the basic airplane type to which the document relates;
(2) Summary of the operational statistics of the fleet in terms of hours and flights;
(3) Description of the typical mission, or missions;
(4) The types of operations for which the inspection program is considered valid;
(5) Reference to documents giving any existing inspections, or modification of parts or components; and
(6) Duration of evaluation validity.
c. The document should contain at least the following information for each critical part or component:
(1) Description of the primary structure susceptible to WFD
(2) The estimated threshold of MSD/MED and subsequent occurrence (hours/cycles) of WFD;
(3) Recommended initial inspection threshold;
(4) Recommended repeat inspection interval;
(5) Recommended inspection method and procedure and alternatives;
(6) Any optional modification or replacement of the structural element as terminating action to inspection;
(7) Any mandatory modification or replacement of the structural element;
Appendix 2
(9) Guidance to the operator on which inspection findings should be reported to the manufacturer.
4. RESPONSIBILITY. It is expected that the evaluation will be conducted in a cooperative effort between the operators and manufacturers with participation by airworthiness authorities during the evaluation.
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