INFORMATION LETTER #2002-1

Sikorsky S-61/H-3 Tail Rotor Blade Corrosion

ABS 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, this will make inspection in the field almost impossible. When you inspect this area of the blade you apply finger pressure 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. With the filler sealed with structural adhesive it is always hard to the touch 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 the moisture in this area and now you may have corrosion. The blade in the illustration now will have to have the pocket, strap and root channel replaced and if this problem was not addressed the blade may be scrap do 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 that the balsa filler has deteriorated and has 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. To replace the root channel in most circumstances the pocket will need replacing also.

Should more information be desired please phone Dave Stutesman at ABS 407-846-6780.