Sikorsky S-55, S-58, S-61 and S-64 Main Rotor Blades
We have seen several blades that have very serious problems. This blade was operated by a logging company that has very high rates of turns per hour and with an extremely high utilization under heavy loading.
These cracks were all found on the bottom side of the blade at the cuff attachment point and all started at one of the mount bolt holes. The cuff attachment point is a very sensitive location on the blade as the required fit between the cuff, spar and bolt is reamed to a very tight tolerance.
The blade shown was removed from service due to the daily B.I.M. inspection. The indicator showed red and subsequently the blade was removed from service. This blade was then sent to another blade shop. It was diagnosed as a tip dam leak and repaired at that time. The blade was then returned to the customer and this problem was again experienced and the same diagnoses was rendered to the customer. The blade was then reinstalled on the helicopter and lasted about 7 hours and again the indicator went red. At that point the blade was shipped to ABS. We then utilized our helium leak detection system and immediately located the problem, the cuff leak at several bolt holes. The cuff was removed, and the true problem was then located.
This situation was quite a shock to all our staff. The customer authorized us to destroy the blade, so we cut the inboard end off the spar and totally reassembled the cuff system. This allowed us to use this portion of the blade for test purposes. We are working with a specialty testing laboratory to devise a method to detect this type of problem prior to failure without disassembling the blade. Removing and reinstalling the cuff end of the blade gets to be very costly and we will do our best to find a method to detect this problem without tearing the blade apart.
The lesson here is the B.I.M. system that Sikorsky designed and installed on its blades works very well if appropriately maintained.