“Plausible” “No firm conclusions” “Similar disasters”
You have pretty well summed it up.

It’s likely, in any operation where the people on board, IE pilots/pax, have any say, that an EC225 won’t be used.

Read post #1916 "between the lines". Each first paragraph sums it up and is a "hole in the cheese".

You can test the gearbox to destruction but that would be pointless unless you had some idea as to what you would do to initiate it.

This is a seriously deep rabbit hole!!

And yet look at that recent report about the S92 in Canada. Ok they missed the sea by 13’ but it was very close. And not the first time. The 225 may have a quickly-detachable rotor head but the autopilot made the aircraft much safer in the face of loss of SA/pilot incompetence. But as ever, unfortunately humans don’t evaluate risk logically or rationally.

It's been a long while since I strapped into a 225, but I dont think this is entirely accurate. The 225 flown without any upper modes would still get you into trouble. The hidden protections would only help with at least 1 upper mode engaged. So in this instance (I dont think the 92 had any upper modes engaged) then the outcome may have been the same. (Assuming the 225 gearbox could take the ramp up in torque that the 92 took)

Look at G-REDU, that flew itself straight in... no upper modes...

Can you link to that report?

S92 Report

:ok: Ten Characters.

I agree about the risk evaluation not necessarily being logical.
The thing that resonates with me is: If the rotor head departs, no matter what, no matter how good or lucky you are as a pilot, you have a few seconds of terrifying life left.
Most of us believe, rightly or wrongly, that catastrophic incompetence can be avoided, or even recovered from, as in the S92 near miss referenced.

Yes I get that. Every pilot thinks it (a major piloting cockup) couldn’t possibly happen to me because I’m not that stupid. But I can’t see how that translates onto the passengers. Whether they crash and burn due to pilot error, or due to system design/manufacture error, surely doesn’t matter to them.

you are correct on a simplistic level. But the point is that the 225’s upper modes are so capable that they tend to get used eg on a visual segment post-MAP, and any sensible operator encourages or mandates it. The S92s upper modes can’t be used at low IAS and anyway are quite soggy, so it’s back to the human and fallible pilot by necessity.

Of course since I left the N Sea in 2013 things have moved on to the 175 and 189, which probably have good autopilots (well the 175 certainly does) but then again, have the fatal design flaws on those new aircraft manifested themselves yet? Who knows!

They can be used at low air speeds on a 92 and are used at low airspeeds, in a DVE the rad alt can be left engaged until committal to give protection. Granted it's not as good as the 225, but they can be used. Simplistic about sums it and me up :E

Anyway, thread drift etc...

But not such a good gearbox with double the removals and 50% of Mil 8 TBOs.

I’d personally describe the 189 AFCS (and FMS) as “disappointing”. Not as good as the 139, and a different league to the 225. I’m hoping for some improvements with subsequent “Phases”.

As an Aircraft as a whole - I really like it (AW189). Hoping for no undiscovered “fatal design flaws”.

That is pretty disappointing. Is there a broader trend, that the more recent helicopters are less durable?
I keep thinking that SpaceX appears to have transformed launch economics by focusing on robustness rather than peak performance.
Is a similar shift in philosophy potentially possible in the helicopter market?

Traditionally, components like Gearboxes seemed to be over engineered, then lifed conservatively.
For safety: Obviously.

Then with fleet information gleaned over time from inspections and testing of “time EX” gearboxes (for example), TBO’s could often (usually) be extended.
For reduced operating costs: Obviously.

Anecdotally, increased competition and greed now mean pushing everything to it’s limit*. For the brochure. Then, when a few fail, reducing the TBO is the easy, and potentially profitable way out, for the manufacturer.

EC225’s had a MTOW of 11200Kg*. What did the Puma start out at 8350Kg? (Or less? - I never flew a non “Super” Puma.)

When I started flying Puma in 1971 the MAW was 6,400 kgs. and the gearbox life was 900 hrs. Around 1973 the AUW was increased to 6,700 kgs and at the same time they initiated the CAAP Programme. (Component advanced ageing programme)

The was a programme to fly selected aircraft; two RAF and four French Army, one hundred hours a month each with the gearboxes stripped every two hundred hours so as to extend the fleet's life to 1800hrs.

This was successful so the Puma entered the civilian market. I flew the 'J' model with plastic blades up to 7.400 kgs.

The EC225 MTOW was 11000 Kg or 11200 Kg with external load.

As I mentioned in a previous post: Too much new wine in old bottles.

I had a chance to convert to them late in my working life but being one of HC's 'Old Dinosaurs' I didn't like the way it was operated so I backed out and stayed on the 332L1.

As we all know it was the same crack in a second stage planet gear on G-REDL on 01.04.2009 and LN-OJF on 29.04.2016, which caused the MR to separate. After all the measures taken, like reduction of the MGB TBO to roughly one third of the initial TBO, installation of another mag plug, flight ban on one type of planet gear etc etc, the 225 could be considered as safe for flight (again), imho. Especially the more frequent scheduled MGB removals drive the costs per flight hours, but who cares.
However, after thousands of engineer hours and millions of Euros for the regarding technical investigation, the reason why a crack (twice) could propagate inside the gear rim, undetected by e. g. HUMS and the classical methods like mag plug and filter, remains still unknown. Strange, isn't it?

There is quite a bit more to this story. Airbus announced in September 2019 that they had determined the root cause, but as far as I am aware, has still never released any of this information into the public domain. There may be many reasons for not releasing this information, but none of them bode well for Airbus, as secrecy in the realm of accident investigation is a dangerous path to tread and may result in the unintended consequence of challenging their overall credibility.

AIRBUS HELICOPTERS FINDS ROOT CAUSE OF THE TUROY H225 CRASH | OGPNetwork

OGP NETWORK OIL GAS & POWER LATEST NEWS

AIRBUS HELICOPTERS FINDS ROOT CAUSE OF THE TUROY H225 CRASH

By
OGP Network
-
September 13, 2019 On April 29, 2016, one H225 Super Puma helicopter operated by CHC Helicopter, en route from Gulfaks B to Bergen, went down close to the small island of Turoy, west of Bergen, Norway. All 13 occupants of the heavy-twin, two pilots and eleven oilfield staff died within the accident after the primary rotor separated from the plane at 2,000ft. The lack of the primary rotor in flight is essentially the most dramatic accident that may occur to a helicopter. There are not any phrases to explain it.

The UK journal Flight Global reported that Airbus Helicopters has recognized the basis explanation for the primary gearbox (MGB) failure behind the deadly 2016 crash of an H225 in Norway. In its last report in July 2018, Norwegian investigators decided second-stage planet gear within the MGB’s epicyclic module had failed as a result of sub-surface cracking and fracture of a bearing race. However, they have been unable to say what had triggered the occasion.

“The investigation has proven that the mix of fabric properties, floor remedy, design, operational loading surroundings and particles gave rise to a failure mode which was not beforehand anticipated or assessed,” the report says.

But the airframer has continued its personal evaluation of the occasion, says H225 programme director Michel Macia, resulting in identification of the basis trigger and a profitable replication of the failure in testing. That work has been externally validated, he says. Findings from that effort have been subsequently shared with Norway’s SHT accident investigation physique, regulators together with the European Union Aviation Safety Agency, and different producers, says Macia.

“Everyone now is aware of that the basis trigger is known and has been reproduced,” says Macia. Although he declines to element the failure, he says the security obstacles put in place to allow the H225 to return to service take care of the underlying difficulty. These measures embrace a heightened inspection regime, shorter life limits on elements and – considerably – the exclusion of one of many two totally different bearing designs used on the helicopter.

The H225 and the associated AS332 L2 have been grounded for 4 months following the crash, and though each at the moment are cleared for service, they’ve but to be introduced again to operation within the North Sea area for offshore transport. While that’s largely as a result of overcapacity within the sector, there stays vital opposition from the oil and fuel workforce to the H225.

But Airbus Helicopters chief government Bruno Even nonetheless believes the rotorcraft could make a comeback within the North Sea and says the plane wants time to realize acceptance.
“We are doing all that we’re capable of do, however ultimately, it’s the buyer who has to determine.”
The UK Civil Aviation Authority says its place on the H225 has not modified and it has but to obtain an software from an operator to renew H225 passenger flights within the nation.
(Source: Flight Global – Image: Aibn/Super Puma rotor on Turoy Island)

Last year I was in a meeting with M. Macia and his key engineers regarding this issue. What I've understood is that, in Airbus opinion, each cracking of the planet gear (which is coincidentally the outer race of its bearing) starts unavoidably with producing a particle from this outer race. Secondly the crack has a certain progressing time. For the particle they now have a third Full Flow Magnetic Plug with a catch rate of more than 90%. And for the growing of the crack in the rim they have the safety barrier to remove the planet gear every 1000 h (SLL). After all I still have doubts if really each crack will start with a particle. And even if, the particle easily could get lost inside the mgb housing before reaching one of the mag plugs. I'm not convinced of anything until an technically understandable reason for the failure is pinpointed.

Has anyone considered the resulting stresses from combining the bearing and gear components? When one designs a gear one is principally concerned about the tooth bending stress and the contact stress on the flanks of the teeth. I have never designed anything similar to a high speed rolling element bearing but I would think it would be mainly about contact stress but in a different format to the intermittent contact stress on a gear tooth flank.

So if two components are mounted together with a bearing inside a gear there is extra material (and thus weight) and many of the stress influences are isolated within each individual component. If one forms a bearing race as part of the gear, there is less material and fewer stresses are isolated because there is no helpful component boundary. There is a cycle of bending nearer the outside of the component caused by two or more gear engagements and a cycle of contact stresses nearer the inside of the component caused by contact with the rolling elements. The component has surface heat treatment so that material properties on the surfaces of the component are stronger and more brittle and the core remains less strong and more ductile. Everyone hopes that the core ductility of their surface hardened component will deal with the more quirky stresses and development testing should prove it. However, in my head I can visualise the combination of stresses having an effect like peeling up an old piece of lino.

According to Airbus all the different stresses were taken into consideration. Due to the hardened surface of the bearing races and teeth,16NCD13 layer after a nitrid process, and the "weaker" material inside the rim (M50), stress usually peels of the hardened surface. Resulting in flakes, splinters etc. on the mag plug. Which gives an early warning of the degradation. What was new in the G-REDL and LN-OJF case is that only a very limited such surface particle production - if any at all - took place during all the hours where the crack has grown inside. After a lot of time spent trying to understand what happened, my last idea was resonance frequency. In the MGB you have a lot of shafts, gears etc. turning with different speeds, inducing frequencies into the system. What if, in addition to the mentioned stress, the planet gears are exited with a frequency closed to their natural frequency? In combination with a micro pitting in the bearing race, as starting point, this could explain the crack growth inside the rim. Consequently a slightly different rotor speed could lead to a different planet gear behavior. According to this theory a crack would not grow even if initiated by a pitting, if the MR Rpm is e. g. 263 instead of 266 or vice versa.

Resonance is an interesting one. One could have different aircraft seeing different levels of risk based on random variations through acceptable tolerance in avionics settings, engine set-up, gear machining, and so on, plus the variations in load cycles across the fleet. Surely someone has visited these ideas?

All what's said is correct. However, for the gears and bearing materials currently used by the industry (and not only Airbus) it is sheer impossible to improve the products in a way that no spalling or micro pitting will occur anymore. The two main micro pitting drivers are corrosion and the overrun of particles. You couldn't use stainless steel in bearings because it tends to brittle. And you could micro filter the oil as much as you like, you'll never reach 100 % purity, respectively could avoid that particles are overrun in the bearings. Bearing spalling accures since decades on all gearboxes of all manufacturers. What was new is that two planet gears cracked through, most probably initiated by the micro pitting just discussed. So the question is why the planet gears on other h/c models, using the same materials, do not tend to crack through under the same conditions? The only answer which makes sense is that it must be, however, the design. So Airbus had only two options to bring the 225 back in service. Option one would have been a complete new design of the epicyclic, Millions of Euros spent into a product with an unpredictable future. Combined with the admission that the existing design was faulty. Option two was staying with the design, reducing the service life and installing a third mag plug. It's obvious why they have choosen option two.

I think the 225 is out of the medium civil helicopter market for other reasons now: The design looks dated, its too narrow with just three seats in a row, you cannot stand up in it and it's reputation leaves much to be desired.
I flew Pumas and Super Pumas from 1971 to 2008.I have retired and so should the basic design.

Hi Joe .... my comment is about ... "how the crack grows undetected"

I followed this investigation closely (read everything) back in the day ..... a small surface crack may not progress on its own unless there was a flaw in the original metal (rare in this case) ...... the problem is the rolling bearing is compressing oil at a very high pressure that causes hydraulic fracturing into the crack which causes it to keep growing over time.

Same physics that can split a granite rock when a drop of water seeps into a crack and freezes and expands.

Also, the DOC’s are probably comparatively high these days. Only made worse by the reduced TBO on the MRGB

One the other hand, it is the best ride out there. Always my favourite way home. Smoother than all the rest, with those big escape windows, jettisonable big doors, good run-dry spec, good flotation spec. If you know of a large rotorcraft that has done 12 years of intensive CAT without a fatality, please let me know.

PMSL
That’s classic!!!

Thanks - I needed a good laugh.

”Arrrgh, somethings happening - we have some red lights. Do we need to spray Glycol into the MRGB to stop it melting? Can’t really tell - might be a sensor. Spray it in!!? Ok.”
“Did it work? Can’t really tell. Want to wait and see if we get vibrations and/or grinding sounds? No - run the ditching check list.”

Reminds me of the classic “Explosive bolts” scene on “Dr Strangelove” (Peter Sellers 1964)
”Explosive bolts. Negative function”