North Sea heli ditching: Oct 2012
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Though an issue with the nitrided steel alloy bevel gear vertical shafts has clearly been identified, we have yet to determine why the MGB EMLUB caption illuminated (Further investigative work is planned) despite the emergency lubrication system having worked normally - Glycol sprayed in the main gear box and remaining amount of Hydrosafe 620 in the reservoir -
This special bulletin only details progresses being made through the investigation as clearly stated, no final analysis at this stage, right?
This special bulletin only details progresses being made through the investigation as clearly stated, no final analysis at this stage, right?
Here are links to the subject of carburizing v. nitriding
What is the cost difference between carburizing and nitriding? | Eurotherm Products and Solutions Blog
Case hardening - Wikipedia, the free encyclopedia
I don't understand much of it, but if all that was changed in the EC225 shaft design was the case hardening process, then what is to prevent EC from producing new shafts using the old process, which gave no trouble for 4.5 million hours?
What is the cost difference between carburizing and nitriding? | Eurotherm Products and Solutions Blog
Case hardening - Wikipedia, the free encyclopedia
I don't understand much of it, but if all that was changed in the EC225 shaft design was the case hardening process, then what is to prevent EC from producing new shafts using the old process, which gave no trouble for 4.5 million hours?
Some news about Bond 332L2 :
North Sea operator Bond to resume Super Puma flights | Vertical - Helicopter News
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North Sea operator Bond to resume Super Puma flights | Vertical - Helicopter News
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The problem now becomes one of how to spin the story because of the seemingly repeat failure.
Given the time that has passed they can not just come back and suggest that all they needed to do was change back to their old spec.
As I said before this is going to become a case study and the longer it gets dragged out the bigger the mess becomes.
Given the time that has passed they can not just come back and suggest that all they needed to do was change back to their old spec.
As I said before this is going to become a case study and the longer it gets dragged out the bigger the mess becomes.
Does all this beg the question...."What provoked EC to alter what was working just dandy all those years and hours?" That by itself is going to be an interesting story that they probably really do not wish to discuss in polite company.
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Does all this beg the question...."What provoked EC to alter what was working just dandy all those years and hours?"
Just saying like...
Might be something to do with upping the MTOM by 17% from the L2 to the 225 and slapping another blade on the head.
I don't buy that. How long have we been operating these superb machines on the North Sea? Seven-ish years and many thousands of hours.
If nothing got changed in the gearbox during this period, then to my tiny mind such failures must have occurred long before now.
And another thing upsets me. What on earth possessed CHC Scotia not to do MARMS downloads after every flight since the May ditching? It feels like unforgivable negligence to me. Cavalier or what!
I don't buy that. How long have we been operating these superb machines on the North Sea? Seven-ish years and many thousands of hours.
If nothing got changed in the gearbox during this period, then to my tiny mind such failures must have occurred long before now.
And another thing upsets me. What on earth possessed CHC Scotia not to do MARMS downloads after every flight since the May ditching? It feels like unforgivable negligence to me. Cavalier or what!
From HeliHub : Eurocopter issues EC225 “Key Messages”
Eurocopter issues EC225 “Key Messages” | Helihub - the Helicopter Industry Data Source
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Eurocopter issues EC225 “Key Messages” | Helihub - the Helicopter Industry Data Source
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Interesting isn't it:-
Aircraft equipped with nitrided shafts:The first-generation carburized vertical shafts are not concerned.
One assumes they have now moved on from the shaft numbers M330 after the production change and now are focused on material spec. Although it will be interesting to see what changed that view other than simply running down a failure list that was available in the summer.
Aircraft equipped with nitrided shafts:
- All EC225/725, as the nitrided shaft is the only design certified for this aircraft type.
- Some AS332/532 are also equipped with nitrided vertical shafts and as a consequence they are also concerned by the limitation
One assumes they have now moved on from the shaft numbers M330 after the production change and now are focused on material spec. Although it will be interesting to see what changed that view other than simply running down a failure list that was available in the summer.
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And another thing upsets me. What on earth possessed CHC Scotia not to do MARMS downloads after every flight since the May ditching? It feels like unforgivable negligence to me. Cavalier or what!
S3/2012 appears to be telling us that the part of the shaft in question was air spec 16NCD13 in the old shaft and air spec 32CDV13 for the new shaft. It is not clear to me what the construction method is for the entire shaft assembly or what the materials are for the other components of the welded assembly.
16NCD13 (old) is an alloy steel presented as a case hardening spec. Tensile strengths of up to 1380 MPa can be achieved. This material has less carbon and less other alloying elements than the newer shaft. Case hardening adds carbon to the surface of the component and typically gives hardnesses of around 700HV/58Rc. Once heat treatment is complete, core and surface properties are different.
32CDV13 (new) is an alloy steel presented as a nitriding spec. Tensile strengths of up to 1350 MPa can be achieved. Nitriding converts certain alloying elements (such as Vanadium) at the surface to nitrides and typically gives similar hardnesses of around 700HV/58Rc. Vanadium is key to the nitriding properties (to spot a nitriding steel, look for V and Ti) but higher levels of chromium and molybdenum also contribute. Once heat treatment is complete, core and surface properties are different.
To most people, 700 Hardness Vickers (about 58 Rockwell C) gives the impression of glassy hard. This surface layer is much harder and stronger than the core. Hardness and tensile strength aren't everything though and a balance needs to be struck between strength and ductility. There is no point in having a very strong component if it cannot absorb the flexing and shock loads of the application. Making things stronger can appear so simple but it is usually a nightmare of conflicting requirements and properties.
How these materials respond to welding is likely to be under intense scrutiny at the moment. Welding different alloys together can be problematic. Different carbon content in each component would be one area of concern. It would be interesting to know the order of processes in the manufacture of these shafts since that might reveal the properties at the time of welding.
JimF
(Automotive background. Spec'd case hardening and nitriding steels for engine components in the past.)
16NCD13 (old) is an alloy steel presented as a case hardening spec. Tensile strengths of up to 1380 MPa can be achieved. This material has less carbon and less other alloying elements than the newer shaft. Case hardening adds carbon to the surface of the component and typically gives hardnesses of around 700HV/58Rc. Once heat treatment is complete, core and surface properties are different.
32CDV13 (new) is an alloy steel presented as a nitriding spec. Tensile strengths of up to 1350 MPa can be achieved. Nitriding converts certain alloying elements (such as Vanadium) at the surface to nitrides and typically gives similar hardnesses of around 700HV/58Rc. Vanadium is key to the nitriding properties (to spot a nitriding steel, look for V and Ti) but higher levels of chromium and molybdenum also contribute. Once heat treatment is complete, core and surface properties are different.
To most people, 700 Hardness Vickers (about 58 Rockwell C) gives the impression of glassy hard. This surface layer is much harder and stronger than the core. Hardness and tensile strength aren't everything though and a balance needs to be struck between strength and ductility. There is no point in having a very strong component if it cannot absorb the flexing and shock loads of the application. Making things stronger can appear so simple but it is usually a nightmare of conflicting requirements and properties.
How these materials respond to welding is likely to be under intense scrutiny at the moment. Welding different alloys together can be problematic. Different carbon content in each component would be one area of concern. It would be interesting to know the order of processes in the manufacture of these shafts since that might reveal the properties at the time of welding.
JimF
(Automotive background. Spec'd case hardening and nitriding steels for engine components in the past.)
it is interesting Jim although you would like to think that Eurocopter and its parent the €22bn market cap. EADS might have the resources to understand that?
Maybe they had "made in China" stamped on them?
Maybe they had "made in China" stamped on them?
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The future?
It's not difficult to imagine that those who are responsible for buying helicopter services are going to find it difficult to trust the design/manufacture/certification processes ever again. There will be those who would prefer going back to older designs that are mature and are better understood by those that fly and maintain them.
If new designs are to be accepted by the end users then the certification process needs greater transparency and a more questioning authority. Having made that point it will be difficult for the certification team to get their heads around innovative designs unless they have been exposed, from the earliest possible point in the development process, to the thoughts and computations used by the OEM.
It is quite stunning for this non-technically qualified pilot to hear that the design of both the S92 and the 225 used single pathways for the activation of both main and back-up oil pumps that serve the single most important component in the drive train - the Main Transmission Gearbox. Tell me I have it wrong somebody - please. I cannot believe this is true - I must have misunderstood.
G.
If new designs are to be accepted by the end users then the certification process needs greater transparency and a more questioning authority. Having made that point it will be difficult for the certification team to get their heads around innovative designs unless they have been exposed, from the earliest possible point in the development process, to the thoughts and computations used by the OEM.
It is quite stunning for this non-technically qualified pilot to hear that the design of both the S92 and the 225 used single pathways for the activation of both main and back-up oil pumps that serve the single most important component in the drive train - the Main Transmission Gearbox. Tell me I have it wrong somebody - please. I cannot believe this is true - I must have misunderstood.
G.
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How many rig workers can tell the difference between the 225 and l/l2? I mean no disrespect to the workforce, I just know I struggled to tell the difference until people showed me what to look for....
How many rig workers can tell the difference between the 225 and l/l2? I mean no disrespect to the workforce, I just know I struggled to tell the difference until people showed me what to look for....
G-CHCN ditching incident - Step Change in Safety
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Originally Posted by Geoffersincornwall
It is quite stunning for this non-technically qualified pilot to hear that the design of both the S92 and the 225 used single pathways for the activation of both main and back-up oil pumps that serve the single most important component in the drive train - the Main Transmission Gearbox. Tell me I have it wrong somebody - please. I cannot believe this is true - I must have misunderstood.
The pumps are driven by the one shaft that never stops when we are airborne, the main rotor shaft.
Each pump has its own gear on that shaft that it is driven by.
The standby pump is lower with a lower intake to draw the oil in reducing the amount of pipework necessary.
The end result is no one looking at that design prior to these two incidents would imagine the shaft(s) shearing and causing this problem. So credit to Aerospatiale when they designed the Superpuma system that the 225 inherited.
Si
Biggles is probably soundly asleep by now, so I'll answer for him with one word, Yes. As I said earlier, I've seen it with my own eyes so I know it is so.
Instead of a weld, I would favour something like a spline joint into the MR shaft. But that would take years to certify.
Instead of a weld, I would favour something like a spline joint into the MR shaft. But that would take years to certify.
Last edited by Colibri49; 20th Nov 2012 at 15:56.