Sikorsky S-61/H-3 Tail Rotor Blade Corrosion
Aviation Blade Services has received tail rotor blades part number S6117-30101 and S6117-30201 from various operators for repair. This blade has an additional balance weight system in under the root-end filler to provide an additional cord-wise balance means. The root-end filler is still manufactured from balsa wood and sealed with clear lacquer.
Several blades have been received with the balsa insert sealed with structural adhesive, which made inspection in the field almost impossible. When this area of the blade is inspected finger pressure is applied to the filler to determine if it is soft, if so you replace this filler I/A/W your Sikorsky maintenance manual, see below Figure 4-20. The filler is always hard to the touch if sealed with structural adhesive but the adhesive will dis-bond from the sides of the root-channel allowing moisture to enter the cavity.
As seen in the picture below the balsa filler holds moisture in this area and now there may be corrosion. The blade in the illustration had to have the pocket, strap and root channel replaced. If this problem had not been addressed the blade may have to have been scrapped due to the corrosion damage to the spar.
This notice is for information purposes only and does not condemn any blade without a more detailed inspection.
Most tail rotor blades where the balsa filler has deteriorated and have moisture present take additional labor to repair and static balance due to the corrosion of the balance weight retaining bolt. Many of these blades will have to have the screw drilled out with out damaging the nut plate. The nut plate is installed in the root channel prior to installing the assembly in the blade. In most circumstances to replace the root channel the pocket will need replacing also.
Should more information be desired please phone Leonard Peterson at 407-846-6780.