Originally Posted by
Concentric
You ask a couple of very good questions. I think it raises further questions too.
I do not mean this as criticism of the AAIB but if you look at their report on G-REDL, section 1.18.2 it states that:
“Data provided by the helicopter manufacturer indicated that between 2001 and 2009 there were nine recorded cases of planet gear spalling on the AS332 L2 (see Table 2)”
and then goes on to add that:
“The information provided by the manufacturer regarding the number of planet gear rejections due to spalling was incomplete. During the investigation anecdotal evidence was provided that indicated that overhaul facilities disposed of rejected gears without routing them for investigation”.
As the EC225 and AS332L2 are widely reported to share the same epicyclic gearbox module, isn’t it surprising that only data on L2 gears with spalling was considered relevant? Was the Type 2 gear introduced for the EC225 to use exclusively, therefore considered to not be relevant to the 2009 investigation? Something doesn’t add up here.
From the report:
Components rejected, in operation or during overhaul, were inspected in accordance with the Continued Airworthiness programme. Those which were considered to show new or unusual failure modes were then routed by the manufacturer to its materials laboratory for further analysis. However, the laboratory did not have the capacity to carry out an investigation of every component rejected during gearbox overhaul. When the Continued Airworthiness programme for the AS332 L2 was initiated it was determined, based on previous operational history, design calculations and the maintenance programme requirements, that damage to the planet gear outer race would not adversely affect the continued airworthiness of the helicopter. Therefore, planet gears which had been rejected for spalling were not routinely routed to the laboratory for additional investigation.
I think that was more of a capacity problem, rather than not of interest.
It is disturbing though, that they did not take action to investigate every one of them.
But the failure risk experienced on the L2 was assessed on the 225 by means of
decreasing the TBO.
Originally Posted by n305fa
Re the prediction of remaining gear life with spalling present, I was referring to your assertion that the gear should have lasted 300 hours, not the ability of the design team to predict residual life based on certification testing.
Sorry I don't follow you. I'm referring to the given running time and the TBO.
So 1080 to 2000 hours is 900 hours. It ran 300 hours until failure from last
modification, inspection and repair, whatever that means. According to the certification testing, it could have some spalling at 2000 hours that would not lead to catastrophic failure.