"Just for others to clerify things please see drawing
there is actualy 3 sets of bearing, one set in the bottom of shaft, one just above where the shaft cracks, and one above the epicyclic gear"

Okay, I stand corrected. The shiny part IS for a third bearing which wasn't in place when I looked up into the bottom of a gearbox. But it seems to be there to support against side loads from the reaction to torque driving the pumps, which was bothering me so much.

Even so, when the fractures occurred and the shaft was no longer driving the pumps, there would have been the main rotor shaft bearings still doing their job and the pump drive shaft would have stopped turning.

It might not even have dropped much at all, but there would not have been a noticable imbalance to the pilots and certainly no bearings and metal chunks thrashing around to do further damage.

Well, I live and learn and many thanks to FBav for the diagram on the previous page.

Pass me another slice of humble pie, please.

Referring to FBav's diagram on page 24, and also from a Eurocopter drawing of the 360 fracture, it occurred very close to the horizontal line at the top of the conical shaft, above the hole in the conical section.

I've just removed the second paragraph because of uncertainty as to what I'm looking at, probably mistakenly identifying as bearings.

gearbox design
 

Just some clarifications about some of the posts of today:

1. There is a manufacturing reason why the weld is in that place, such kind of bevel gears are finished before welding, because, with an "integral shaft", you physically can't grind the teeth (grinding wheel shall impact with the shaft)

2.If you look at the gear mesh, you see that it is above the weld, no significant torque is transferred to the bottom part of the shaft, below the weld, but "flows" to the top, to the epyciclic stage. What is reacted by the two roller bearings are the side loads of the mesh, i.e., the bending effect on shaft due to axial and radial forces of the bevel gear mesh. I will not speculate on actual stress value or margins of safety, but this is why the bottom shaft looks "thin", there is only bending stress, not bending + torque stress.

3. respect to the Main Rotor Torque, the effect of the pumps should be quite marginal (how many KWs for 2 pumps respect to the MCP...?), besides, they are driven by spur gears, that is, no axial or radial forces are introduced, so no significant side forces.

Not sure about the above below weld bit in point 2 for the pumps, probably a typo but the rest is good stuff. Keep it comming.

Just reread your post, Your quite right. (in my opinion)


(in my opinion) added as an edit.

Yes.

If we consider a point near to the weld, there is limited torque because that part of the shaft drives only the pumps. This limited torque results in a small shear stress.

The separating force of the spiral bevel (caused by the pressure angle of typically 20 degrees) is that which acts upwards and inwards from the centreline of the pinion towards the centreline of the rotor shaft above the epicyclic. This results in a moment that tries to tip the spiral bevel wheel away from the pinion. The reaction to this moment at the lower roller bearing (near the pumps) is of a similar scale to the gear separation force. However, at the weld, because it is significantly closer to the centre of the moment, the forces are higher. This results in bending stress at the point we are considering.

As the spiral bevel wheel turns, the bending stress oscillates from positive to negative. This oscillating stress component is far higher than the shear stress, or any stress due to the weight of the shaft or the reaction of the pump gears, and is the dominating stress in the area of the weld.

The splines for the epicyclic input gear are a small distance above the spiral bevel wheel. Since the spiral bevel wheel is a very substantial component and the input gear is a thin-walled component, it seems unlikely that there is any force from the driving of the epicyclic influencing the weld area.

Thin-walled shaft with holes in it subjected to oscillating bending stress. Interesting.

dascanio- I agree with your comment regarding the location of the weld. The bevel gear shaft is made in two pieces to allow milling & finish grinding of the gear teeth. In a previous post (before I saw the nice cross section drawing), I speculated that the joint was a friction weld. But since the weld appears to have been made after finishing of the bevel gear teeth, it most likely is a laser or EB weld.

Another interesting feature shown in the cross section drawing is that the oil pump drive gear is separate from the shaft. It appears to be attached with some sort of internal threaded faster and possibly a narrow curvic face coupling(?). The joint seems to be just below the lower roller bearing. There is also a separate inner bearing race clamped in place by the pump gear.

Thanks to FBav for the nice drawing. Very interesting discussion.

New bulletin from EC, I need someone more versed in EC documents to explain i and confirm my understanding.

Si

Given the comments here:- EC225

I'm not really sure what value add any new bulletin will give??

It would appear from the latest revision to Emergency Alert Service Bulletin 04A008 that EC share my concerns about the viability of half a shaft and a reduction in supporting bearings.


Text size edited.

Is there any practical advice or they just communicating further concerns......

"EC share my concerns about the viability of half a shaft and a reduction in supporting bearings."

Looking at the diagram and considering that it is very unlikely that the high torque and load bearing section of a MR shaft would be designed with a welded join, I must agree with the quote from Helicomparator.


"It definitely cracked above the bottom bearing, leaving the 2 other bearings to support the main shaft, one being just above the bevel gear (and hence taking most of the bevel gear side loads). I thikn the intention is that the bottom bearing doesn't take much except the pump gear side loads"

Colibrì, the power required to drive the two pumps is minimal, respect to, say, MCP,( less than 10 HP, I imagine), their contribution to the Bearings reaction is truly minor, the side force of the two spur gears being very small, respect to the balance of the bevel gear. The bottom roller bearing is there to support the Shaft, its main loading IS due to the bevel gear mesh, and the bearing is smaller than the top roller one because (like in a lever...) its load is inferior since its distance from the gear mesh is bigger.

From Emergency Alert Service Bulletin 04A009 Rev 2

In case of bevel gear failure, the top part of the bevel gear continues transmitting the power to the main
rotor, but all the meshing loads are transferred to the upper bearing.
Following the investigations conducted on the 2 bevel gears, it was found that this bearing and the meshing
part of the bevel gear were in good condition after having operated during
almost 10 minutes after failure. Supported by the calculations performed, EUROCOPTER is therefore
confident that in similar cases, the 30 flying minutes permitted by the Flight Manual after activation of the
emergency lubrication can be performed without worsening of the scenario.
Nevertheless, EUROCOPTER will launch tests to demonstrate the latter. Pending the results of these tests,
a new procedure requiring immediate landing is defined for this specific case.

The whole SB is worth a good read. Bottom line at the moment EC thinks the shaft can last 30 mins in this condition, but untill they can prove it an immediate landing is require.

I hope by now the queries on how the main gearbox is constructed with regard to the shaft and the purpose of the various bearings has been established to everybody’s satisfaction.
I would now like to move on to another aspect of the current situation.
6,4.5,X what is X
X being the time in hours between a MOD45 MARMs acquisition showing the start of a crack and the next shaft failing.
EC predict this figure to be 4.5hrs that’s why you are allowed to fly for 3 hours after a successful in limits MOD45 acquisition, this allows a 50% safety margin.
Up until yesterday the measures in place were flawed. The measures at that time allowed an aircraft that had just completed a 3hr flight with a single MOD45 acquisition at the beginning of the flight to depart on another 3 hr flight. With the times between detection and failure being 6hrs and 4.5hrs for the first 2 incidences it was possible to lose another shaft, despite MARMs monitoring.
Today we have to consider the available time for a flight is dependent on when the last MOD45 acquisition took place.
All of this is dependent on accurately predicting X.
EC predict X to be 4.5. On the 25 July after the first incident EC issued a statement saying The probability for another component to be equally affected is extremely low. We all know how that prediction went.
I hope x is 4.5

So if Iunderstand your post Pablo you are saying that the clock starts at data downloadtime and not from the actual time of the alarm?? I take that from your comment:-



“The measuresat that time allowed an aircraft that had just completed a 3hr flight with asingle MOD45 acquisition at the beginning of the flight to depart on another 3hr flight.”



Is thatbecause there is no way to look at the whole of the data in detail - forinstance like this:-



http://us1.webpublications.com.au/static/images/articles/i1082/108255_4lo.jpg



This is asimple example of some race car data which in this case looks like a MagnetiMarelli system. The X axis being time, theY axis displaying the range of a variety of inputs. So here you can see clearly if a thresholdwas breeched you could see exactly when that might be.



Otherwiseyou are left with a system that says during this period the threshold wasbreeched and if that is the case the safe option would be to assume it happenedat the start rather than at the end!!



Beinteresting to here how it works.

In any event the message the current bulletin gives is terrible and reliesentirely on the emergency lubrication system and a punt that the hunches arecorrect from a bunch of people who have been proved to have not that good at predictingthe future.

Pittsextra
The MARMs information is displayed on download as separate acquisitions. For an acquisitions to be made in the first place the aircraft needs to be in a stable state. If the aircraft is not within certain parameters no acquisition is taken. If you are flying to rigs with a lot of straight and level you would probably get a couple of acquisitions per hour. If you are logging or constantly training you may never get an acquisition.
You can tell from the download at what point in the flight time wise the acquisition was made.
Previous to yesterday the requirement was to check the download at the end of the flight and if the MOD45 acquisition was below the limits and no significant upward trend was noted the aircraft could go for another 3 hrs. This was reasonably fine for people who do a lot of straight and level with lots of acquisitions. However it didn’t cater for the people with a low number of acquisitions, the change is to tighten up on the foreseeable possibilities of operation.

Yes I understand the stable state logic and I guess they have increased the priority for data collection for the relevant components. Although given the sweep of data collection takes around 30 minutes and the helicopter to be in a normal flight regime some condition indicators might not log very much data. In fact it would be interesting to see a data table for what is actually logged.

The time critical nature of indentifying a faliure and the effective lack of reliable data within timescales that correlate with the short time available to indentify any failure mean that with the current system its very hit and miss.

Especially given the need to indentify a significant up trend... So what is that absolutely??

As for flying on for 30 mins well forget that, it is the single most stupid piece of advice anyone could give.

Edited to add :- if you can tell from the download time at what point in the flight the acquisition was made why does the 3 hour flight time not start from that point??

Also I understood that if no data acquisitions had been made for 10 hours flight time it would flag?

Also:-

So its taken a month to figure this out? EC on the ball.

if you can tell from the download time at what point in the flight the acquisition was made why does the 3 hour flight time not start from that point??


It sort of does with effect from yesterday.

Edited to add

Also I understood that if no data acquisitions had been made for 10 hours flight time it would flag?

I may be wrong but I think you get a warning after 5hrs. At the moment if you don't get information for more than 3 hrs you have to NDT the shaft.

Its a mess and effectively the thing is grounded because its got so confused to the point that no one really has a good hand on this.

But its pretty clear the issue is accepted so how and why now?

Of the EC225's you run what is the highest hours?

I am not type-rated on these aircraft, but when I read the new EASA AD (released in the last 24 hrs) I got completely lost in the detail. Some of the detailed discussion was also less than reassuring, it seemed to me. The rationale still seems to rely on VM giving 100% reliable advanced warning, prior to failure.

Does anyone who thinks they understand where we are now want to give a summary in plain English?

Have any defective masts been detected prior to failure using the MARMS?
If so how many?

Yes I'll have a go.

Much of the detail in the reason is sad and winding tale of how we got where we are now justifying the reasons and rational of prior AD's. Then we cut to the chase which is to try and keep these things in the air no matter what. (at some point the cockpit is going to be so littered with notices that forward viz might be an issue! - thankfully the CAA are not playing this silly game).

So the lastest one basically says with reduced torque that helps, that you can perform a check on the vertical shaft in situ that if you have M'ARMS check it and check it again and that there is now issue with AS332's.

With respect its becoming a bigger joke with each release and it feels like nobody at EC has a grip on this because the level of checking and restriction on the type show that essentially the EC225 is still FUBAR and the investigation is on going.

Someone needs to explain risk / reward to Eurocopter and EASA because the reward for limping on in this way is blown away by the downside of having another accident.

In summary don't get onboard an EC225 or AS332L2, I'll certainly be refusing to fly on one in the unlikely event either of these Super Puma variants appears on our helideck again!

But this only applies to the post mod shafts, none of which are flying in the north sea, so theres no reason to not get on an L2 Moody

AS332 with the old type shafts are unaffected by this AD although this effectively brings EASA, in a gentle way, into line with CAA for EC225 as it is practically impossible to comply with it in North Sea operation given the flight hours before check, maintenance flight or inspection of the MGB.

Things appear to getting far to serious here.
Letts lighten the mood with a little survey of all the engineers that might be watching.
With regard to the Mlube system.
Did you find the N0 1 engine interface (A) bizarre no gasket and the clamp appears to have an imperial nut on it. Strange for a metric aircraft (B) apparently designed for the job.
P2.4 valve had any problems? (A) almost always leaks, to one degree or another(B) appears designed for the job.
P2.4 intercooler. (A) There is no A (B) designed for the job
Hose intercooler to P2,4 pressure sw manifold. (A) strange angle should have had a 45 degree angle on it.It always looks crushed(B) designed for the job.
Pipework from manifold to MGB. (A) how do you test that without removing the box? (B) designed for the job.
Glycol pump had any problems (A) not since I installed the replacement (B) designed for the job.
Maintenance panel had any problems? (A) it appears to dispense glycol into the MGB every time I put the battery on post maintenance, (B) appears designed for the job.
Pressure switches had any problems? (A) not to my knowledge apparently someone has quite recently. (B) Appears designed for the job.
Procedure in maintenance Manuel for testing M lube system (A) please don’t interrupt me I’m searching the hanger to coble something together. I’ve no chance of reproducing the Mk 1 regulator as I’m a new operator my makabel kit looks nothing like the picture trying to find something to fit the hose from the engine is doing my head in, how the hell do you get shop air to test it with at the required pressure without the P2.4 valve sounding like its about to mutate (B) designed for the job.

Edited to remove poor spelling.

Funny that you should mention "Manuel" when it seems like Basil Fawlty could have had a large part to play in this shambles.

My bad. apparently I dident remove enought bad speeling.

HELINUT & MOODYMAN - where we are now is clearly explained on the Eurocopter website.

EUROCOPTER are testing an EC225 in the air at the moment in an attempt to isolate the cause of the crack in the shaft. They will continue to test until they, DGAC, EASA, CAA and AAIB are satisfied that they have identified the root cause. When they have identified the root cause they will set about working out how to overcome the problem in consultation and agreement with DGAC, EASA, CAA and AAIB. This is science not speculation.

EUROCOPTER are benchtesting a complete EMLUB system in order to establish the root cause of the erronous EMLUB failure indication under the appropriate MGB operating conditions. They will follow the same procedure as for the MGB until rectification is achieved.

In the meantime EUROCOPTER have issued an ASB to establish some interim management protocols for other variants that may be affected pending identification of the root cause.

This is a complex problem and EUROCOPTER cannot move forward without the agreement of at least 4 independant authorities.

I would suggest that the kind of science currently being deployed in the EUROCOPTER facilities far exceeds the experience and understanding of majority of the postings on this thread (including mine).

MOODYMAN - PM me and we can talk further about your worries re the 225/L2

DB

DB with respect your comments about the future do not stand the test of the recent past and even the current!

Currently even though EASA have moved closer to the CAA's treatment of the 225 they still do not hold a common view. The AAIB are just a reporting body and will be guided by the CAA/EASA. So qualify what this means:-

Currently this is very far from science. Given what has happened explain the latest EASA AD which is the what 4th or 5th ammendment and tell me where science plays any part?? Its a total embarresment.

The MOD45 data is so flakey that you might not even get reliable data for as many as 10 flight hours - so when you have a problem that might need attention within 3 flight hours you have a directive which just fudges things to work around.

Its not beyond people here because much of the solution is common sense and yet so far we have seen a total absense of common sense from EASA and Eurocopter.

Moodyman - until this has a proper analysis and remedy just stay away from the type. At the moment they assume the AS332 is ok on the old shaft and yet nobody can tell you why. Is it design or material for example.

Is there any truth in the rumour (doing the rounds at ABZ) that one operator discovered a crack in a shaft when it was boroscoped post the ditching although there had been no indications on MARMS up to this point? If this I true then I think it puts a completely different slant on things. I find it hard to believe that an operator or EC would keep this quiet....

PITSEXTRA - seeing as you seem to have all the answers why bother griping. Just phone Eurocopter and tell them the solution.

Telling a PAX to stay away from a type is fine but make sure include ALL the other types that have actually caused a loss of life.

DB - THe only answer I have is to stop guessing at the answer and for EC to be brave and stop the drip drip of info that leads to further restrictions and work load on the ground crew that is a road that leads to those guys being over loaded and finger trouble. You know it does.

You said before :-

Is the same testing to isolate the cause that led to a particular set of shafts, that then wasn't when the October accident happened??

Good job.

Yes of course there are other types that have gone down but you know its the process here that is incredible. I mean whilst we are talking AS332L2 you might recall the accident that claimed REDL in April 2009 still had EASA Emergency (emergency!) AD's in July 2012 (see 2012-0129-E).

And in that AD it says:-

"Since issuance of EASA AD 2009-0099-E, the UK Air Accident Investigation Board published the final accident report. On the basis of these investigation findings, it has been decided to standardize the intervals of the visual checks of all electrical and non-electrical chip detectors, and to require this check for all models of the Super-Puma helicopter family, in order to increase the likelihood of detecting any adhered particles. This action must be accomplished on all rotor drive system gear boxes, i.e. on the MGB, but also on the Intermediate Gear Box (IGB) and the Tail Gear Box (TGB)."

Well the AAIB report into this was November 2011 so it took 8 months for EASA to the react but then and you might ask why is it the AAIB/EASA leading the way here and not the OEM?

Frankly I think it calls into question the quality of people at EC.

DB given your attitude to safety on another thread, trying to be-little peoples concerns is a poor show. Tell me do you think this has been handled well or that EC has done the right thing??

Hmmm, let's ask HeliComparator...?

I'm sure the fact that Eurocopter are probably paying his salary won't influence his answer at all :rolleyes: