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Old 12th Oct 2016, 04:57
  #65 (permalink)  
Concentric
 
Join Date: Jun 2016
Location: Aberdeen
Posts: 87
Originally Posted by birmingham View Post
"There are two configurations of planet gear within the current type design. In depth review of the design and service data showed that one configuration has higher operating stress levels that result in more frequent events of spalling, associated with rolling contact fatigue, while the other exhibits better reliability behaviour. By limiting the type design to the gear configuration with lower stress levels and better reliability and specifying a reduced life limit, combined with more effective oil debris monitoring procedures and other operational controls, an acceptable level of safety can be restored."

Redesigning an epicyclic is hardly a trivial exercise and there must have been a very good reason to do so. I don't know the engineering history of this does anyone know if it was in response to earlier failures or simply to increase time between inspections or allow higher loadings?

Also were all the previous MGB accidents (excluding the bevel gear systems) involving type A?
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.

Last edited by Concentric; 12th Oct 2016 at 07:35. Reason: Everything becomes clear after a cigarette.
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