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Old 12th Oct 2016, 15:17
  #67 (permalink)  
Concentric
 
Join Date: Jun 2016
Location: Aberdeen
Posts: 87
Originally Posted by industry insider View Post
Concentric

There are 2 types of gear with different part numbers -06 and -07. Each gear has bearings from a different manufacturer. -07 gear bearings have a different span and shape and a corresponding greater contact pressure on the outer race (inner rig of the gear) than -06 gear bearings.

It is thought that the greater contact pressure of the bearing in the -07 gear causes spalling. The -06 gear bearing is not known to suffer spalling according to AH.

Any metal on the plugs or in filter at the 10 hour inspection must be analysed. Any presence 16NCD-13 metal would indicate spalling of the -06 gear bearing. The -06 gear / bearing / cage combination has been in the L and L1 for some time and are regarded as the reliability benchmark.
Thanks for that info. On reading EASB 63A030 it looks like there are more than just 2 part numbers, in fact -00, -02, -03, -04, -05, -06, -07. Of these the ones I marked in bold appear to require replacement. So what you say appears to be a subset of this. The total number of type-07's listed is 2972 (over 370 gearboxes).

From the AAIB report 2/2011:

"The design of the AS332 L2 MGB was based on the design of the L1 model, and used essentially the same main module as the L1. In order to maximise the benefits of the increased engine power between the L1 and L2, changes were made to the epicyclic gearbox module. These included increasing the size of the second stage epicyclic planet gears and reducing their number from nine, in the L1, to eight. These changes not only took account of the increased power to be transmitted, but were also aimed at reducing the probability of spalling".

So the AS332L1 planet gears are not the same as H225 type B gears (or type -06 if you like)?

Last edited by Concentric; 12th Oct 2016 at 15:28.
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