77-20-06 PILATUS AIRCRAFT, LTD. AND FAIRCHILD HILLER: Amendment 39-3050. Applies to Model PC-6 airplanes (all variants) manufactured by Pilatus Aircraft, Ltd., up through S/N 724 and to Model PC- 6 airplanes (all variants) manufactured by Fairchild Hiller, S/N's 2001 through 2047, certificated in all categories.
Compliance is required within the next 25 hours time in service after the effective date of this AD, unless already accomplished within the last 75 hours time in service, and thereafter at intervals not to exceed 100 hours time in service from the last inspection, until the conditions of paragraph (c) are met.
(a) To prevent a hazardous degree of corrosion from developing inside the wing struts, accomplish the following:
(1) Visually inspect the internal surface of each wing strut for corrosion in accordance with paragraph 2.1 of Pilatus Aircraft Ltd., Service Bulletin No. 105, dated May 1971, (hereinafter S.B. No. 105) for Pilatus manufactured airplanes or paragraph2A of Fairchild Hiller Service Bulletin PC6-57-3, dated July 15, 1971 (hereinafter S.B. PC6-57-3), for Fairchild Hiller airplanes, or an FAA-approved equivalent.
(2) If only light corrosion (corrosion which has not caused surface blistering) is found during an inspection required by paragraph (a)(1) of this AD, within the next 100 hours time in service or within the next 60 days after finding the corrosion, whichever occurs sooner, remove the corrosion from, and apply an anticorrosive treatment to, the inside of the wing strut in accordance with paragraph 2.3 of S.B. No. 105 or paragraph 2D of S.B. PC6-57-3, as applicable, or an FAA-approved equivalent.
(3) If corrosion is found during an inspection required by parargraph (a)(1) of this AD which has resulted in exceeding the limits prescribed in paragraph (a)(2), within the next 100 hours time in service or within the next 60 days after finding the corrosion, whichever occurs sooner, replace the wing strut with a serviceable strut of the same part number that has had anticorrosive treatment applied to the inside surface in accordance with paragraph 2.3 of S.B. No. 105 or paragraph 2D of S.B. PC6-57-3, as applicable, or an FAA- approved equivalent.
(b) For Pilatus Aircraft, Ltd., Model PC-6 airplanes, S/N's 338 through 701, to prevent a hazardous degree of corrosion from developing on the wing strut attachment brackets, acocmplish the following:
(1) Visually inspect each wing strut attachment bracket for corrosion in accordance with paragraph 2.1 of Pilatus Aircraft, Ltd., Service Bulletin No. 93, dated June 1969, (hereinafter S.B. NO. 93) or an FAA-approved equivalent.
(2) If only light corrosion (corrosion which has caused 2% to 10% reduction in cross-section per paragraph 2.2 of S.B. No. 93) is found during an inspection required by paragraph (b)(1) of this AD, within the next 100 hours time in service or within the next 60 days after finding the corrosion, whichever occurs sooner, remove the corrosion and apply an anti-corrosive treatment to the wing strut attachment bracket in accordance with paragraph 2.4 of S.B. No. 93, and reinstall the bracket in accordance with paragraph 2.5.1 of S.B. No. 93 or an FAA-approved equivalent.
(3) If corrosion is found during an inspection required by paragraph (b)(1) of this AD which has resulted in exceeding the limits prescribed in paragraph (b)(2) of this AD, within the next 100 hours time in service or within the next 60 days after finding the corrosion, whichever occurs sooner, replace the wing strut attachment bracket with a new wing strut attachment bracket (P/N 111.35.06.055 (left) or 111.35.06.056 (right)) in accordance with paragraph 2.5.2 of S.B. No. 93 or an FAA-approved equivalent.
(c) The inspections required by paragraph (a)(1) or (b)(1) of this AD may be discontinued, in accordance with the following:
(1) Inspection of the wing strut when the strut has had light corrosion removed and has had the anticorrosive treatment in accordance with paragraph (a)(2) or when the strut has been replaced in accordance with paragraph (a)(3) of this AD.
(2) Inspection of the wing strut attachment bracket when the bracket has had light corrosion removed and has had the anticorrosive treatment in accordance with paragraph (b)(2), or when the bracket has been replaced in accordance with paragraph (b)(3) of this AD.
This amendment becomes effective November 3, 1977.