Originally Posted by
henra
These epicyclic gears are hardened and if thrown clear, falling free and hitting rock from 2000ft it is easily conceivable that they would break apart
I'm not convinced that is very likely. Hardened steel is brittle but also very strong. It's likely to be much harder than any rock it would hit on impact, meaning that the rock would probably take most of the damage. I don't know what the terminal velocity for such a gear is, but I assume the weight to air resistance factor is relatively low meaning that the terminal velocity will be somewhat limited. In addition AIBN indicated that the corrosion came from the gear parts having spent time in salt water. Although it would be possible for it to land on a rock and bounce into the water, I find if more probable that they landed in the water in the first place. The overview map also indicates that these were found in the sea.
Originally Posted by
AAKEE
The other two is the rear ones, on pictures in the report. One of them seems not connected(rear hand aft ?) to any hinge in the picture of the rotor in my link above...?
The hinge doesnt seem to be broken and the bolt and pin is not connected on the picture in the preliminary report.
How could we explain that one strut rod seems to lack of hinge connector for the helicopter body, but the hinge is not broken, nor is the bolt ?
The way I interpret the picture of the aft suspension bars is that they (AIBN) have removed the 3 bolts and that that they came down connected to the rotor. My guess is that the 4. bolt is jammed in place by deformations either from when the helicopter came apart or when the parts landed, and that they have left it there to not disturb this deformation if it should need further investigation.
It's still don't know what to make of the bar/rod in the picture or the rotor head, it looks like the lower end of one of them without the mounting/attachement attached. At the same time, the pins can't have been missing since they're all among the found parts and the bolts all seems in one peace. If the bolt and pin is installed there is no way the suspension bar can be detached from the mounting/attachement without any of the parts being broken, so something doesn't add up here. Maybe the mounting/attachement already had been removed on the ground before the picture was taken as this was considered a cruical part to secure?
I'm no expert in this field in any way, but I've always considered the missing pin theory a bit to "easy", and I think they would have a bit more warning signs that 1-2 seconds if that were the case. I've experienced pins breaking and bolts sliding out for the bucket on an excavator some times, and once the bolt lets go of the first "side" you will either break it or it will deform and give you a lot of slack. Since these bolts probably is very hardened, My guess is that the bolt would break before it would move all the way out as long as it had any load on it.
If I'm going to speculate I think the incident two(?) days before the accident deserves more attention. I've read so many articles about this by now so I don't recall what were the exact sources for every bit of information, but unless I'm completely mistaken the incident was described in the press as a "yellow engine warning light" that came on. They then replaced some "engine" part (I never trust journalists to be very precise about such things, so it could be anything), the warning light was still lit and then changed something else and the warning light went away and the aircraft was put back into use. I also read somewhere else that there is some kind of live "analysis" of the HUMS data which lights a "yellow warning light" if something is found to need attention. It's unknown to me whether this system is the "extra safety" system that were installed as a result of the two earlier gearbox failures and removed when the new gearbox was installed or if there's still some live analysis of the HUMS data in corrolation to a yellow warning lamp.
I know that there are loads and loads of warning lamps in there, and that a "yellow light" isn't enought to make any connection as such, but my imagination can't help but think that there could have been a problem triggering some automatic analysis - to which they couldn't figure out the exact cause. If they first replaced one part and tested, and the replaced a second one it indicates to me that they wasn't exactly sure what caused the warning, and the warning could go away even if they didn't fix the underlying problem (for example because they could have "treated a symptom" instead of the root cause).
I'm not saying it's something here, I just think it's strange that with all this speculation I've seen nothing about this possible connection.