47-27-01 WACO: (Was Mandatory Note 4 of AD-648-1.) Applies to Models UKS-7, VKS-7, VKS-7F Aircraft.
Compliance required not later than next periodic inspection.
Inspect tank area in wings for damage to plywood tank support and wing spars caused by collection of moisture in the boxed area of the fuel tank.
1. Remove the left and right fuel tanks and inspect the condition of the plywood tank support and the front and rear spars.
2. If the plywood supports are found to be in poor condition they should be replaced using new plywood.
3. If the spars have been affected by the accumulated moisture, repairs should be made in accordance with FAA requirements or in extreme cases the spar should be replaced.
4. In order to provide drainage of the tank compartment three holes 3/16 inch in diameter should be drilled through the plywood support at the extreme rear of the support as close to the rear spar as possible without damaging the spar. These drain holes should, of course, extend through the fabric covering.
5. The drain holes should be drilled in all tank compartments at the time the fuel tanks are removed for this inspection.
(The above inspection and recommended remedial measures also covered by Waco Aircraft Co. Service Letter No. 3.)