AD 97-13-11 was issued to address an unsafe condition and accident caused by fatigue cracks occurring in the lower spar caps. AD 97-13-11 was superseded by AD 97-17-03, AD 2000-11-16, AD 2003-07-01, AD 2006-07-15, and AD 2009-26-11. AD 2009-26-11 requires repetitive inspection of the 1/4-inch and 5/16- inch bolt hole areas on the wing front lower spar caps for fatigue cracking, repair or replacement of any wing front lower spar cap where fatigue cracks are found, and replacement of the wing front lower spar caps when a life limit is reached. Prior to or after wing front lower spar cap replacement, if replacement via Avenger STC SA03654AT is not chosen, options are provided for the required repetitive inspections based on the various available methods for replacement. The FAA is concerned these options, as provided by Table 3, Table 4, and Table 5 of the AD, could be misinterpreted.
For the maximum inspection interval (Table 5) to be used, which is every 900 or 1,250 hours time-in[1]service (TIS) based on the inspection method utilized, Thrush Custom Kit CK-AG-41 Rev A must be followed in its entirety. No deviations from the instructions of CK-AG-41 Rev A are allowed in order to be eligible for the maximum inspection interval. This includes all parts contained within the kit, and any additional parts noted as required due to different aircraft or wing configurations.
If CK-AG-41 Rev A is not followed in its entirety, but the “big butterfly” plates and lower splice plates of the custom kit are installed as part of the wing front lower spar cap replacement, then this will allow forthe inspection interval prescribed in Table 4 of the AD, which is every 450 or 625 hours TIS, again depending on the inspection method utilized.
The minimum inspection interval of 250 or 350 hours TIS (Table 3), must be followed if only the affected or both wing front lower spar caps are replaced, with no additional structure.
For all replacement options, no parts are to be reused if replacements are provided as part of CK-AG-41 Rev A.
