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INFORMATION LETTER #1996-1

Sikorsky S-55 and S-58 Main Rotor Blades

Some operators are having trouble or have had trouble balancing Orlando Blade Technologies (OBT) overhauled main rotor blades. This problem seems especially bad when running OBT blades with Sikorsky, Military or ABS BIMed blades. During our investigations into this problem brought forward by several operators we discovered that when OBT BIMed the blade they occasionally decided to remove some weight from inside the spar. A simple test is to take a strong magnet and run it along the spar just aft of the leading edge, you can feel the pull of the magnet on the steel balance weights. When measuring from the tip end of the spar there should be 235” of weights installed. OBT typically removed 24” of additional weight during their BIM installation procedure. Total weight removed is from about 2.2 lbs. To 4.4 lbs. This was then compensated for by increasing the amount of weight in the tip end of the blade in the span-wise balance position. Thus the blade has less weight and also is cordwise out of balance.

So please be aware that when installing a blade that was BIMed by Sikorsky, the Military, or ABS across from an OBT BIMed blade you may experience difficulty in your track and balance exercises. Usually you can tell if OBT BIMed the blade by inspecting the log card of the blade. They should have signed off the installation of the BIM system, “installation in accordance with Sikorsky Service Bulletin 58B15-4M.”

If you are currently running 4 OBT BIMed blades together quite possibly you won’t notice this until you swap one or more blades with blades not converted by O.B.T. Then you will probably blame the new blade(s) for not flying with the others. Also should you send in a blade, we will have to correct this as it is not in compliance with the type certificate or the manufacturers drawings.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

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