To: helo_44
What Robinson has told you may very well be correct but three failures for the same reason on three helicopters in the same area (Improper starting procedures). Gears fail for many reasons one of which is abuse and overstress. However they also fail due to improper machining (A lot of S-58 T tail rotor gear boxes failed for this reason). Other gears fail due to faulty heat-treat where the gears are either too hard or not hard enough. (There were 43 B-214s that had bull gears that were too soft and had premature wear). There is such a thing, as batch sensitivity where parts are made at the same time and if one has a problem then there is a strong possibility that the other parts made at the same time will have the same problem.
When the gears are removed if you can check the manufacturing date to see if they were made at the same time. Even if they were not made at the same time have your maintenance engineer check the wear pattern and the Brinell hardness of the gear body.
