Again, simple answer: yes

agreed. Indeed there is more than one.

Diversification; There is no way that a company of HS/CHC's standing operating a contract for Statoil would knowingly use old parts (unless part of a fully approved refurbishment program with full traceability). There is an outside chance it would happen without their knowledge but so many systems and checks are there it is next to impossible. There have been a number of statements made about maintenance and we haven't yet had the report. But the standards these guys work to are the highest in the world. We should certainly give them more than the benefit of the doubt until some evidence is produced. I don't know any more than anybody else but I would be very surprised if they weren't entirely exonerated.

birmingham: who did the overhaul? (CHC or Heli-One, the company referred to in this thread). I would expect that item by item documentation of critical dynamic components is part of an overhaul contract's paperwork and audit trail. This is the kind of stuff a QC or QA department must review/verify before calling the overhaul complete / satisfactory / up to standards.

The problem with the bevel shaft affecting the planet theory is that it would probably affect first stage. Not to say it didn't end up that way, we don't know. First stage sun was worn uneven. About the only thing that one could logically speculate to be related.
Could also be a general local starvation of oil in the epicyclic module. Clogged passage could do that.
To me, looks like gears ran very hot and discolored.
Chip detector won't work without oil return flow.

But if oil return flow stops, doesn't the cockpit get an indication? Temps going up?

@Lonewolf_50: I don't know the 225, but I don't know of any helicopter with an indicating system that senses oil return flow (or oil supply flow for that matter, whether that be in an engine or gearbox).

Oil temperature, where a thermocouple is inserted into an oil flow line or sump somewhere, obviously requires oil to be in the system for the probe to measure the oil temperature. If oil system volume is decreasing you should see an increase in temperature as the available oil is spending less time cooling down before it's heated up again. But you need to be looking at the gauge, I don't think there is an oil high temp warning on a CWP?

And oil supply pressure, usually on the output of the integral oil pump/s built into or on the gearbox (or engine). Oil pressure should be dual function, low pressure switch and pressure transmitter. Without oil you might not see a high temperature indication, but you should see a low oil pressure indication, and a low oil pressure warning on the CWP.

If there is an anomaly in the oil flow circuit somewhere (such as a blocked oil jet), you might only get a slight increase in the oil temperature indication, but still within the normal range.

I guess most people here know all this anyway.

No sh!t.
If the pilots had any kind of warning it would have taken them 30-40 seconds to do an emergency descent and put down on any kind of surface, rock or sea. If the rotor departed 5 or 10 feet before landing they would all have had a good chance of surviving the madness.
Timing is everything.

Good point. Gear rim fractures are most likely to initiate at the tooth root fillet surfaces where tensile stress is concentrated. With current design practice, the gear rim section under the root fillets is made thick enough (typically >1.25 times the tooth whole depth) so that any fracture initiated at the fillet propagates thru the adjacent tooth rather than through the rim. Loss of a single tooth is preferable to failure of the rim structure.

Here is a good read on the situation with a thin section planet gear supported by a spherical roller bearing, if anyone is interested.

@dascanio, @Never Fretter, @Pablo332 & @Satcomm:

By http://www.pprune.org/rotorheads/578...ml#post9398712 I have put into the discussion facts to bevel gear and shaft and no rumor or trolling!

Furthermore I simply asked „The big question is now: Are there new evidences given, that ’Shaft 3’ might be one of the multiple causes of latest accident in Norway?“

One of the facts is that first stage sun was worn uneven. It is a further fact that a problem with the bevel shaft is affecting at minimum the first stage of planet gear, not to say it will end up that way!

So, why are you trying to piss on my feet without any facts and evidences?

AH did exclude without any evidence the bevel gear and shaft problematic within the first 48 hours after the accident and also created a lot of other stories, which proofed to be nonsense.

I am of the opinion 'A liar will not be believed even when he speaks the truth. This spirit runs like a red thread through the history of (Super) PUMA, NH-90, AH-TIGER, A400M, EUROFIGHTER, EUROHAWK and the UAV-Scenario” and I have already told this in http://www.pprune.org/rotorheads/578...ml#post9393708

@dascanio: Maybe I was involved in my forty-five years carriere in military and commercial aviations in more AAIB as you dream? As a consultant I am engaged in a project which doesn’t allow me to use “H120“ or “B505X“ as a nick, otherwise my client would become a little bit angry.:p

I think this issue has been mostly rectified at least in the 'civilised' parts of the world. What I do wonder is if while changing/disassembling the MGB a mishandling could cause damage to the outer race of a bearing/epicyclic gear?
Roller bearings are normally very robust when running and very fragile against shocks while being static. Could a ding while changing/disassembling/handling the MGB cause a small damage/dent in the race that then started to propagate? How is this prevented, especially in such a combined design with hardened surfaces on both sides (inner and outer side)?

@AW009: unfortunately you are mistaken. The sun gear extremely worn you are referring to is, actually, the SECOND stage sun gear, that is integral with the first stage planet carrier. The first stage sun gear is driven by the bevel shaft, but is below, and is not integral with the bevel shaft. Therefore, you are looking, ref AIBN report of the 27th, pic 5, to the a second stage component, i.e. The sun, actually.
A failure of the bevel shaft, as evidenced in the previous accidents, causes immediate loss of power to the pumps, and is identified by zero oil pressure, I imagine this is the reason why AH said almost immediately this is not the same situation as the previous two (2012) accidents.
Therefore my previous comments; besides riff raff in one of his previous posts, attached a cross section of the gearbox that is quite self explaining

I still think that a serious and thorough investigation is under way, and should be respectful for the victims that the investigators are left doing their job.
Regards

*deleted* Sorry

AW009 it is trolling to raise unsubstantiated and inaccurate accusations in the form of a question and then ignore the correct answer! Even more so to be demanding extensive evidence from others, while you continue to churn out irrelevant and unjustified sanctimonious nonsense.

Zalt, I agree 100%.

gulliBell,

The only aircraft that I know of that does the above is the S92, however, only for the input modules. My understanding is, the left MGB oil pump is responsible for scavenging the left input and the right MGB oil pump for scavenging the right input. Basically there is a vacuum switch in the oil return from the modules and if the vacuum is lost then the cockpit gets an indication that the left or right pump has failed. If ignored, there will be a rise in oil temp with an eventual over temp of that input. Pretty sure standard procedures are to reduce power to the effected side until landing. Again, this is only for the inputs, anything inside the MGB module itself would have no indication.

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

I understand from reports, that the CVFDR had only about 2 seconds of recording of the incident and the aircraft crashed. I don't believe any mayday calls were made. This I feel is what makes this accident so scary. There was nothing the aircrew could have done to survive.

Towerdog

But of course they didn't because the whole MRH departed, so your point is?

There are some pretty creative fools out there