EC225 crash near Bergen, Norway April 2016

[turboshafts]

Hi,

the systems for an aircraft has to be fault-proof

the same is valid for the maintenance

I assume that the gearbox is test driven (as claimed) to the extent
that any damage due to the mistreatment could be indentified.

However, I have found something interesting.

With respect to the LN-OPG accident, I have read the report again
to understand a bit more further the strategy of the ongoing investigation.

It is written explicitly in the report, that gearboxes are interchanged
between helicopters in the fleet. The same is said for the engines.
After overhaul they could be mounted on any aircraft of the type (per my understanding).

so that leads me to the following point.
even in the LN-OPG accident, the maintenance history was investigated.
And from there it was reported that during MGB overhaul it was also
found pitting on the inside surface of the planetary gears. But the gearbox was still
rebuilt as it was claimed to be not of influence on the operation (as claimed in report)
Even this gearbox was testdriven and found faultproof.

The LN-OPG accident was however due to the splined part of the bendix input shaft breaking and engine overreving.

Now, with respect to the findings in the investigation of that accident I find it hard to understand that the TBO was increased from 3000 hours on the L1 to 4400 hours on the EC225?

If pitting could be found and reinstalled and put to service.
How come that they react so stringent to the fact that it is fatigue cracks on the current gearsets of the EC225?

If pitting occurs on any gear, it means that the surface is not holding up.
could be many reasons for that. but in all engineering, we know as well
that a surface that pits, might also develop hair thin, stochastic cracks in the surface finish that eventually will lead to fatigue cracks.

sorry to say, that it is found that the gears have fatiuge cracks, doesn not give me the impression that a solution is found, when in 1997 the gears with pitting could be rebuilt without any concern.

Is the maintenance program fault-proof for the ec225? as it was for the L1?

with all do respect, for those involved in the maintenance, design, flight etc.
this is not an attack on the job you made.

i just want to ask a question.

would the disasters have happened if the TBO was 2500 hours?

I have read the report of the Cougar S92 accident as well.
1 out of 16 detrimental factors that lead to the accident was that a metal particle
was found in the gearbox during overhaul, not deemed of importance
and the gearbox was rebuilt.

Was fatigue cracks one of many factors that could ultimately
be traced to the fact that a more stringent maintenance could
have avoided the accident?

I think it´s a fair time to open that discussion