INFORMATION LETTER #1997-2

Sikorsky S-55, S-58, S-61 and S-64 Main Rotor Blades

CRACK PROPAGATION

As you can see by the following illustration, we have found a couple of blades that have very serious problems. This blade was operated by a logging company that have 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. As you can see, the cracks all started at one of the mount bolt holes. This is a very sensitive location, on the blade. The cuff attachment points are very critical and 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 a red indication 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 was repeated again 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 time the blade was shipped to us. We then utilized our helium leak detection system and immediately located the problem, cuff leak at several bolt holes. The cuff was removed and the true problem was then located.

This problem 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 will allow us to us this portion of the blade for test proposes. We are working with a specialty testing laboratory to try to determine 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 and costing you a lot of money and time.

The good part of this is, the B.I.M. system that Sikorsky designed and installed on our blades works very well if maintained accordingly.

With the many diverse uses the industry is coming up with we will need good programs to help cut the cost of this equipment and still keep our aircraft safe for continued operations.

If any of you have any suggestion at all, no matter how large or small, please call so we can discuss it in greater detail. We all need to work together to solve some of these problems and we need your help and input to make this a better industry for all.

David M. Stutesman
President