Sikorsky S-61/H3/Agusta AS-61/Westland Sea King/Commando
POCKET CORROSION
Upon inspection of 40 main rotor blades manufactured by Agusta, Sikorsky and Westland, we isolated the following problem:
1. We recently completed inspection on 10 each Westland manufactured main rotor blades part number, WD4529-00002-047. By visual inspection and X-ray, we found that 82 pockets out of 230 had severe internal corrosion. Most of the corrosion was on the ribs that support the skin.
The pockets are manufactured in several pieces: the skin, internal ribs and the back wall. There are a number of pocket configurations used on this blade, some have five internal support ribs and the others have eight ribs. The pocket skin, ribs, back wall and adhesive are then assembled in an alignment fixture and heated to cure the adhesive. Prior to assembly, all parts are heat treated for strength and anodized for corrosion resistance.
The Westland manufactured pockets we inspected revealed severe corrosion present on an abnormal amount of support ribs. Some interior skin had corrosion present, but in small amounts, and the back wall showed no corrosion problem. This problem may have stemmed from the process used to manufacture the ribs or in the anodize plating process used.
In field operations many of these pockets may be found by inspecting each pocket for rib integrity by applying external pressure on the pocket skin, by applying light hand pressure to determine if the ribs are structurally sound.
2. Aviation Blade Services received 10 each Agusta main rotor blades that were stored in a barge in excess of 100 days. We found an average of 12 pockets per assembly of Agusta manufactured rotor blades that were replaced due to pocket internal and external corrosion. Out of the 10 blades inspected, 4 were removed from service due to spar corrosion beyond allowable limits and 6 were repaired and returned to the customer. With proper storage, handling and shipping the potential for this problem would have been minimized.
3. Over the past 5 years we have replaced a very small number of Sikorsky manufactured pockets due to internal corrosion.
We cannot overly stress the need to properly maintain, store, handle and ship your rotor blades as repairs can become quite expensive. Although the severe corrosion we have repaired has been isolated to the Westland manufactured pocket assemblies and the Augusta blades that were improperly stored, this problem will continue to occur and increase your operational cost if the proper storage and handling rotor blades is not addressed.
The above photo is just one example of a corroded pocket removed from a Westland Sea King main rotor blade. Aviation Blade Services has replaced many that have been corroded to a greater degree. This corroded pocket was found during a visual inspection but many that have not reached this stage of corrosion can only be found by means of X-ray or fluoroscope. Approximately 80% of the pockets replaced on a Westland manufactured blade will be due to corrosion inside the pocket.
Sikorsky and Augusta manufactured pockets have not experienced this specific problem. If they have been replaced due to corrosion it was mostly exhibited on the skin surface but very seldom on the internal ribs. If the ribs are corroded on the Sikorsky or Augusta rotor blade there has always been additional corrosion found throughout the pocket surfaces.
