AD 78-20-06

78-20-06 AIRCRAFT PARTS AND DEVELOPMENT CORPORATION (CALLAIR): Amendment 39-3299 as amended by Amendment 39-3356. Applies to Models A-9, A-9A, and A-9B Airplanes which have the wing struts carry-through tube running through the hopper, certificated in all categories (Airworthiness Docket No. 78-ASW-52).

Compliance required within the next 25 hours' time in service after the effective date of this AD except that aircraft added by Amendment 39-3356 must comply within the next 25 hours' time in service from the effective date of such amendment. To prevent failure of the main carry-through tube, P/N 11013, due to corrosion from exposure to corrosive chemicals in airplanes equipped with the large hopper, accomplish the following:

(a) Deleted.

(b) Remove the hopper top and inspect for a fiberglass wrapped carry-through tube. The main carry- through tube if located in the hopper is located 25 inches aft of the hopper forward bulkhead and six inches below the hopper surface. Visually inspect the fiberglass wrapping for cracks.

(c) If the fiberglass wrapping is cracked, remove all the fiberglass wrapping and visually inspect the main carry-through tube for corrosion.

(d) Remove all corrosion found on the main carry-through tube. If the corrosion removal exceeds a depth of 0.010 inch in one location or 2 percent of the tube cross-sectional area, the main carry-through tube, P/N 11013, must be replaced. The nominal cross-sectional area is 0.42 square inch. Finish the tube with two coats of zinc chromate primer after corrosion removal. Rewrap the exposed tube inside the hopper with a fiberglass laminate. The fiberglass laminate must include a minimum of three layers of MIL-C-9084 glass cloth of the 181 type with a Volan A or Garan 136 finish. Use a Reichhold 33-402 chemical resistant resin.

(e) Aircraft may be flown in accordance with FAR 21.197 to a base where this AD can be accomplished.

(f) Equivalent methods of complying withthis AD must be approved by the Chief, Engineering and Manufacturing Branch, FAA, Southwest Region. (Service information concerning this tubing inspection and replacement may be obtained upon request to Service Manager, Aircraft Parts & Development Corp., L.A.F.B. Building 162, Laredo, Texas 78040.)

Amendment 39-3299 became effective October 4, 1978. This amendment 39-3356 becomes effective December 8, 1978.