Originally Posted by
Apate
turboshafts:
Where did you get the idea from that there were no HUMS readouts?
Originally Posted by nadar
If I recall correcly, the HUMS data for the accident flight determined to be lost since these data aren't stored (but kept in RAM only which loose all information when it looses power)
This is what Nadar wrote. I asked a question, wether it is clearly known if there are no HUMS readouts, or no abnormal readouts.
Originally Posted by n305fa
You can't predict how long the gear should run as the complete gear is not available to fully quantify the damage to the raceway as (I assume) you do not know enough about the gears operational load cycle, effect esn of lubrication, rate of damage progression etc.
Thatīs is why there is an immense amount of durability testing of components.
I would tend to agree with you if it was a completely new design, but this design has operated for years with 1000's flying hours. If you look at the failure modes and
wear prior to failure modes, you are able to accurately predict the life of components, adding a safety factor to it.
Originally Posted by n305fa
THence the use of MCDs as the primary method of detecting epicyclic deterioration (HUMS doesn't work well due to the constant movement of the planets relative to the accelerometers).
The accelerometers are able to measure vibration frequency. As I understood
monitoring a given treshold for the frequency should tell you if it is abnormal operation. It might be the case, exceeding my knowledge, if the G-REDL
and LN-OJF has different positioning of the accelerometers?
Originally Posted by n305fa
The 225 and 332 have plenty of history of detecting spalling of planet gears without catastrophic failure, therefore it is possible that this failure is not due to normal spalling. If a crack forms at the interface of the carburised layer, or in the body of the gear it will only be detectable when it breaches a surface and results in particles being released. This was what the AAIB theorised with REDL and may be a factor in the accident.
Read the REDL report closely. The length of the spalling close to where the crack started is very similar on the two gears
Originally Posted by n305fa
Re the jamming of the gearbox, the epicyclic ring gear damage suggests that something was entrained between a planet gear and the ring gear which burst the case, If the epicyclic had jammed the ring gear and planets would have had significant stripping of gear teeth. There was no suggestion that the REDL MGB jammed
If you look at the outer ring gear of the secondary stage planet,
you will clearly see that on G-REDL it is broken on the same place as on LN-OJF.
What is different as I see it is the fair amount of teeth crushing on the sun gear of the LN-OJF.
In both cases the outer ring is cracked open.
In both cases 1 gear is cracked into several pieces.
Such a failure is fairly stochastic. If there was a piece of the failed gear that
broke and jammed between itself and the sun gear on LN-OJF which cracked
open the case and on G-REDL it jammed between itself and the outer ring gear.