They are used in vast numbers everywhere in engineering.

I don't really see much of a functional difference between the duplex bearing and double or even single ball bearings which expands the installed base even further.

Well, all bearings have some sort of life / failure profile. Off the cuff, I would venture that this application was quite arduous for a relatively small, sealed lubricant bearing so, I would presume that this bearing could fail quite quickly in use after loss of lubricant, or other causes of failure. Can anyone with type knowledge comment if any method of monitoring is used on this bearing?

OAP

This is basically correct. But the "grooves" are stress relieving grooves ground or cut on a radius to prevent a sharp right angle on the shaft material. The outer edge of the inner race of the bearing also has a radius for a similar reason, in addition to ensuring that the pre-load clamping covers the flat face of the bearing without putting any radial force to it which could lead to misalignment.

Basically, thanks for corrupting my correct post Old Farang. ;) But, the groove and the and the step are there specifically to accommodate the engineering needs of the bearing inner races, as I described. Corner radii are used as standard practice and are incorporated as required. If the bearing did not need the inner races to be precisely seated in this way, the shaft would not be waisted by the groove or the step.

OAP

Onceapilot you are right. Groove at the right end of bearing surface is engineering need for manufacturing (free space for grinding wheel/tool for close tolerance work on shaft) and a stress relief, as sharp corners are not desired there - stress/cracking promotion. On the left side - same thing - manufacturing process requirement - transition to close tolerance surface-not a step for spacer. Anyway, spacer should contact inner race freely, to transmit clamping force from nut. Am surprised sketch on S2/2018 report is not correct, as Nodrama suggests.
From photo it is obvious there is a standard right hand thread provided for bearing nut.

Would be of interest to hear what maintenance/servicing manufacturer put in Instructions for Continuing Airworthiness? As mentioned in my post#1123 A-109E had duplex bearing design and lubrication requirements changed considerably, Bell 212 and 412 requires lubrication of this bearing every 50 hours with warning - two shots of grease only.

Thanks for your input hoistop. Between yourself, nodrama, Old Farang and myself, I think we got this covered!:) The next important thing will probably be some clarity from the investigators on why this failure occured. :sad:

OAP

Not a suggestion, fact.

The picture is from the Training School notes, not from an approved Technical Publication.

which will surely come down to installation issues or maintenance issues unless there is a bad batch of bearings out there...then the lawsuits will start flying!

damn, I am so glad you all got this...where would we be without the A team.

That was my original point, which still hasn't been answered. The bulletin clearly says what you say - "the control shaft passes through an outer shaft, which forms part of the … piston"

Is it possible a few degrees of movement occurred, enough to slightly deform but not shear the split pin?

Thank you, you seem to be agreeing with me!
A sectional drawing of this particular unit would indeed be helpful, some of the examples posted have been "schematic" and don't show the arrangement of the control shaft and outer (hollow) shaft.

Understand how the TR will stay where it is, supported by its own bearings. But wouldn't removing and replacing the hydraulic unit be complicated by the fit of the duplex bearing? However, this isn't really relevant to the incident.

What percentage on the #1 Hydro system will auto-close the TRSOV after fluid loss/leakage?

Perfectly explained. So the control shaft is an easy sliding fit through the inner race of the duplex bearing? And it's the castellated nut (and spacer) that clamp the inner race to the step at the outer end of the control shaft?

Only question left is the detail of the control shaft/outer shaft/hydraulic piston, which isn't really relevant.

I appreciate your contribution, however there is something in your delivery that sets the weemonkey "hang on" alarm going...

Thanks ND - also, do you know if hot fluid is the only time an EP permits closing the main 1(2) SOV ?

Yes, understood. That bit is clearly shown in the bulletin Figures.

In spite of the football, it was still a good explanation!

Not quite, but thanks again for your answer. I'm just interested in evolution/progression of Augusta design logic.

Have not seen any updates on investigation. Wondering if I missed something posted elsewhere.
Not sure when updates would be expected.
thanks

​​​​​​Still under investigation no new updates from the aaib since October, not even been changed to finalizing, they must be struggling with something in my opinion.

WuW

I suspect that Covid 19 hasn’t helped with the speed of their investigations.

Perhaps they are just baffled by how a heavily regulated supposedly ultra safe Cat A take off profile with all those engines can still manage to crash and burn...

Perhaps you are right chop, I have followed you for awhile, I can't help but think this is one rare instance that hindsight quick thinking thought processes couldn't of turned this pilot into a hero :(, I try to stay in the background on this forum, this thread gets to me, RIP to all involved.

WuW

Is this not the one where the tail rotor bearing failed resulting in the tail rotor not rotating anymore? What went wrong is known. The causal chain is not (yet public).

Exactly. Having a well supported private aircraft kill everyone on board during a routine takeoff does not inspire confidence.
Evidently there was no obvious design defect, so the investigators are now clutching at straws.

Your ‘Evidently’ interests me. What evidence are you referring to?

​​​​​I believe TR did not lose rpm but went full pitch. The chain of how that happened is all in this thread.

They could be clutching at straws struggling to try work out how a simple component (duplex bearing) can fail in away that's not been seen before and lead to such a catastrophic loss of control and what could be done to prevent it again. Just a opinion :ok:

WuW

No, it was a tail rotor control failure. The tail rotor continued turning but the blades ran to full negative pitch, which is worse than a failed tail rotor drive.

poor maintenance procedures will get you whatever other protections you put in place.

let’s see if this component was ever touched after it left the factory - pretty low hours I think.

Well, none of the above should take anything like as long as the enormously expensive AAIB are taking. And I invite those who think, unhesitatingly, to defend the organisation, to pause for once and consider the facts.

That leaves you with poor design or incorrect installation - nothing you can do as a pilot will affect those.

Monty N

Slightly naive comment, as it is not just the technical members of the AAIB who determine when a report is released. I can think of delayed reports in the past where it has not been the AAIB or the investigation that were the problem, it was the lawyers for the party who appears to be "at fault" and thereby facing financial and reputational consequences, who then tried every avenue to "water down" the report findings before publication.

This particular airframe was one of the first in production, and it had reasonable use. One might therefore expect any issues in design, original build or maintenance scheduling to become apparent on an airframe like this. The information released so far indicates that a duplex bearing in the tail rotor control control mechanism failed and AW issued a service bulletin requiring this part to be checked in all 169 & 189 back in 2018. I guess that both AW and the AAIB know the result of that check, but to my knowledge that result has not been published. It would be interesting to hear from any owner or mechanic who can say what this check found.