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Old 12th Oct 2016, 16:47
  #71 (permalink)  
Join Date: Sep 2007
Location: Birmingham
Posts: 244
Originally Posted by Concentric View Post
A word on probabilities...

This hopefully will be obvious to most people but I think worth mentioning anyway.

In the absence of ‘particular engineered differences’ between the 2 planet gear types, statistically the probability of a failed planet gear belonging to one type or the other is proportional to the number of that type in service as a % of the total.

With roughly equal numbers of 2 types, A & B, in service the recurrence of failure in 2 Type A’s might seem (at first) to point to some sort of particular susceptibility or trend. However this is misleading, for the actual random probability of ‘both gears being of the same type’ remains 50-50 since AA and BB both satisfy that definition. The other side of the coin would have been AB or BA.

It is easy when searching for ‘an answer’ rather than seeking the truth, to accept ‘evidence’ that fits a theory without challenging it objectively.

There now does appear to be some stated ‘particular engineered differences’ between the 2 types but there also appears to remain this lack of understanding as to the cause(s) of these 2 gear failures.
Absolutely - also given the very small number of occurrences the results would not be particularly significant, hence a scientific understanding of why the gear in this accident (and the previous one) failed is essential to restoring confidence.
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