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Old 12th Oct 2016, 16:26
  #69 (permalink)  
Join Date: Sep 2007
Location: Birmingham
Posts: 244
Originally Posted by Concentric View Post
It was mentioned on the crash thread that planet gear types A and B have both been used since introduction of the AS332L2 and subsequently EC225/H225 but are manufactured by different bearing manufacturers. This might simply be for commercial reasons to ensure competitive pricing and security of supply. It has not actually been publicly stated if both crashes involved type A, possibly for legal reasons, but we seem to be steered to that assumption otherwise the change to type B would be foolhardy.

Excluding the bevel gear failures "all" the MGB accidents amount to 2 (the SA330 having a different gearbox). If types A and B are indeed made by different bearing manufacturers then careful perusal of published information confirms both failures were Type A.
Thanks very helpful insight - Despite their admission that the cause is not fully understood the advice is clear - change to type B and up inspections. It is safe to assume that a very thorough evaluation of the service history of the two units has been undertaken and, as you point out, the failures have occurred only in type A. In addition maintenance records must also point to spalling/chip detection data suggesting that type A has proven less durable than type B. If not the advice to go flying is either very brave or very foolhardy. One can therefore assume that the AIBN and AAIB are continuing to examine this theory and obtain more concrete evidence that the problems in A definitely do not exist in B. Proving it happened in A is a very different thing to saying it cannot happen in B hence the extreme caution - the safety and legal consequences of such a statement make it a very high stakes game.

Last edited by birmingham; 12th Oct 2016 at 16:41.
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