AD 2020-16-06 Airworthiness Directives; Aviat Aircraft Inc.

Makes named: aviat. Models named: A-1, A-1A, A-1B, A-1C-180, A-1C-200. Read the applicability below — it usually turns on serial or part numbers too.

This AD applies to Aviat Aircraft Inc., Models A-1, A-1A, A-1B, A-1C-180, and A-1C-200 airplanes, all serial numbers, certificated in any category.

Comply with this AD within the compliance times specified, unless already done.

For airplanes with 400 or more hours time-in-service (TIS), do the following inspection within 30 days after September 1, 2020 (the effective date of this AD) or within 20 hours TIS after September 1, 2020 (the effective date of this AD), whichever occurs first. For airplanes with less than 400 hours TIS, do the following inspections within 30 days after accumulating 400 hours TIS or within 20 hours TIS after accumulating 400 hours TIS, whichever occurs first. After the initial inspection, repeat the inspections at intervals not to exceed 12 months or 100 hours TIS, whichever occurs first. (1) Below and just aft of the horizontal stabilizer leading edge, remove each inspection hole cover if installed, or cut out the inside of each inspection ring if not cut out, on both sides of the fuselage. You do not need to remove the stabilizer support assembly. Locate the forward horizontal stabilizer support assembly. Using a light and a mirror or a borescope, inspect the stabilizer support assembly for cracks in the large tube portion of the assembly. Pay particular attention to the toe of the welded bushings where the stabilizer support assembly is bolted to the fuselage frame. (i) If no cracks are found, install inspection hole cover, part number (P/N) 61659 and mounting screws, P/N 59146. (ii) If any cracks are found, before further flight, replace the stabilizer support assembly with the same part-numbered part, either P/N 35086-501 or P/N 38086-501 as applicable. Replace both self-locking nuts with self-locking nuts that have zero hours TIS. Replacing the forward stabilizer support assembly requires removal and reinstallation of other horizontal stabilizer components. Replace all self-locking nuts with self-locking nuts that have zero hours TIS upon reinstallation of these components. (2) Inspect the rear horizontal stabilizer support tube weld joints for corrosion and damage in accordance with the Instructions, steps 1.a. and 1.b., of Aviat Aircraft Inc. Service Bulletin No. 28, Revision A, dated April 2, 2015. If there is any corrosion or damage on a weld joint, before further flight, repair the weld joint and install a repair tube inside the stabilizer support tube as depicted in the figure on page 3 of Aviat Aircraft Inc. Service Bulletin No. 28, Revision A, dated April 2, 2015. Repairing the rear horizontal stabilizer support tube requires removal and reinstallation of other horizontal stabilizer components. Replace all self-locking nuts with self-locking nuts that have zero hours TIS upon reinstallation of these components.

This AD was prompted by reports of complete failure of the forward horizontal stabilizer support assembly due to fatigue in combination with complete failure of the rear horizontal stabilizer support tube due to fatigue. The FAA is issuing this AD to prevent cracking of the forward and rear inboard supports, which could result in failure of the stabilizer supports, detachment of the stabilizer, and loss of airplane control.

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