AD 70-05-05

70-05-05 AMERICAN AVIATION: Amdt. 39-950. Applies to Model AA-1 aircraft, Serial Nos. AA-1-0001 through AA-1-0159.

Compliance required within the next 10 hours in service after the effective date of this Airworthiness Directive, unless already accomplished, and thereafter at intervals not to exceed 50 hours in service from the last inspection, except as provided in paragraph 3.

To preclude the possibility of exhaust fumes from entering the cabin heat system due to undetected cracks in the muffler, accomplish the following:

1. Inspect muffler and shroud assembly (P/N 14-504001) for cracks particularly in the area adjacent to all welds inside the shroud at the transition between the muffler and the tailpipe. If visual inspection is not possible, pressure test for leaks in accordance with AC 43.13- 1, Chap 14, Section 3, paragraph 287D. If cracks are found in the muffler tailpipe or the muffler shroud they should be repaired by an inert gas-shielded arc welding process such as Heliarc. (Muffler material is AISI 321 stainless steel and shroud material is AISI 304 stainless steel). Accomplish above inspection and necessary repairs in accordance with Advisory Circular 43.13- 1, Chap. 14, Section 3, paragraph 387 and 388.

2. Check alignment between rigid brace P/N 503008-501 and tailpipe to insure that tailpipe is not stressed when brace is installed.

3. The repetitive 50 hour inspection requirement of the exhaust system may be omitted if the aircraft has been altered by installation of a new muffler, Turbo system P/N 099001-113, with the rigid brace.

(American Aviation Service Bulletin No. 116 dated 9 January 1970 covers this same subject)

This amendment is effective March 13, 1970.