EC225 crash near Bergen, Norway April 2016
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With prevailing winds from the southwest, the North Sea is downwind of the UK. After passing over the UK, the wind is more turbulent than wind blowing in off unobstructed ocean. The effects of Welsh mountains can be seen in cloud patterns over Norfolk even though the mountains are hundreds of miles away and not particularly tall by global standards. That is why I make the point that air turbulence in the North Sea is different to that in many other areas.
During the Trials Programs for various HUMS systems and aircraft.....did any Air Tests take place with well instrumented Aircraft that might have yielded Test Data to support your proposition that rough air might be playing a role in unusual stresses upon Gearboxes?
Nigerian In Law
Assuming that was the problem, how has "rough air" (is that a new term ?) on the North Sea been overcome historically ? It's not exactly a new phenomenon. Surely it was windy and turbulent when Wessex was flying offshore ?
NEO
NEO
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I don't have any aircraft test data but there have been well documented cases of off shore wind turbines experiencing significantly higher wear and failure rates than the designers anticipated, especially gearbox failures. So there is a potential indication that North Sea air turbulence is greater than is commonly assumed. The latest wind turbines are built significantly stronger than the original designs.
Maybe it was a particularly smooth and benign 7 years during which I flew on the N. Sea, but I don't recall any markedly rough conditions as a rule . Windy; yes, turbulent sectors on some 'rigs'; yes, but not during normal flight. Conversely, I've had MGB low oil pressure captions come on in the cruise in other arenas.....
I would politely suggest the 'rough air' theory is a non-starter.
I would politely suggest the 'rough air' theory is a non-starter.
Enroute offshore on the North Sea....perhaps I was just lucky but Turbulence was a non-issue....Icing and some other things were.
As to mechanical turbulence off some of the Platforms and Rigs when the Wind got up.....yes sure but as 212Man opined....other places I have flown have shown themselves to be far more violent and prevalent than the North Sea ever was.
As to mechanical turbulence off some of the Platforms and Rigs when the Wind got up.....yes sure but as 212Man opined....other places I have flown have shown themselves to be far more violent and prevalent than the North Sea ever was.
I would politely suggest the 'rough air' theory is a non-starter.
You and SASless may well be illustrating the problem rather than rebutting the argument.
The windmill designers were presumably equally convinced that they had taken the conditions into account when completing their designs. It needed strain gauges on the windmills to convince them otherwise.
You and SASless may well be illustrating the problem rather than rebutting the argument.
The windmill designers were presumably equally convinced that they had taken the conditions into account when completing their designs. It needed strain gauges on the windmills to convince them otherwise.
In case you missed it...five posts before yours....I asked if there were any Test Data from Flight Tests or Proving Tests that would support Gouli's suggestion that unstable air over the North Sea might be playing a role.
He said he knew of none.
We did not "rebut" his argument but offered a response each based upon first hand experience.
You might read back through the thread and see where several of us have questioned the design criteria the AH Gearbox uses and question if ALL of the possible stresses and loads have been considered adequately.
Instead of playing Don Quixote....what are your thoughts to Gearboxes on Helicopters in flight and exactly how rough air might affect them as compared to Windmills firmly attached to the surface?
He said he knew of none.
We did not "rebut" his argument but offered a response each based upon first hand experience.
You might read back through the thread and see where several of us have questioned the design criteria the AH Gearbox uses and question if ALL of the possible stresses and loads have been considered adequately.
Instead of playing Don Quixote....what are your thoughts to Gearboxes on Helicopters in flight and exactly how rough air might affect them as compared to Windmills firmly attached to the surface?
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In considering possible external factors for the gearbox failures I was making the assumption that the AH engineers had factored in all of the normal stresses and strains to be expected in flight.
There is a possible alternative which may not have been picked up by the monitoring programs.
Continuous vibration monitoring is great at picking up sudden changes in vibration levels. A sudden jump indicates that something in the rotating system has changed. Visual inspection is usually sufficient to identify the fault at that stage.
However constant vibration at a particular frequency that does not change over time is considered to be fine and a good sign that everything is functioning normally. This view may be totally wrong. Vibration at infrasound frequencies of 10-20Hz has been proved to cause embrittlement of metal and other substances.
Helicopters being a collection of vibrating rotary parts, a constant level of vibration at around 20Hz might be accepted as perfectly normal if it doesn't change over time. The vibration is however slowly degrading certain components. Rotors could delaminate, gearboxes fail, fastening bolts suddenly snap under load.
A rotor blade starting to delaminate should be detected very quickly. Failed fastenings should also be picked up during standard walkaround inspections. Internal gearbox components are hidden away and difficult to assess without a full strip down.
The point being that if infrasound is a factor there may well be no indication of impending failure until a gear tooth or something else actually snaps off.
Interestingly these sound frequencies frequently cause feelings of foreboding and discomfort in humans exposed to them.
There is a possible alternative which may not have been picked up by the monitoring programs.
Continuous vibration monitoring is great at picking up sudden changes in vibration levels. A sudden jump indicates that something in the rotating system has changed. Visual inspection is usually sufficient to identify the fault at that stage.
However constant vibration at a particular frequency that does not change over time is considered to be fine and a good sign that everything is functioning normally. This view may be totally wrong. Vibration at infrasound frequencies of 10-20Hz has been proved to cause embrittlement of metal and other substances.
Helicopters being a collection of vibrating rotary parts, a constant level of vibration at around 20Hz might be accepted as perfectly normal if it doesn't change over time. The vibration is however slowly degrading certain components. Rotors could delaminate, gearboxes fail, fastening bolts suddenly snap under load.
A rotor blade starting to delaminate should be detected very quickly. Failed fastenings should also be picked up during standard walkaround inspections. Internal gearbox components are hidden away and difficult to assess without a full strip down.
The point being that if infrasound is a factor there may well be no indication of impending failure until a gear tooth or something else actually snaps off.
Interestingly these sound frequencies frequently cause feelings of foreboding and discomfort in humans exposed to them.
Some of us must be exceedingly susceptible to that malady!
I think I am one of them....many a time I have had those exact feelings over the Years. Sometimes while in helicopters too.
I think I am one of them....many a time I have had those exact feelings over the Years. Sometimes while in helicopters too.
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The only thing that can really be taken from the AIBN statement is they haven't yet established why the fatigue occurred with a sufficient level of confidence to agree that the removal of one type of planet gear assembly and adding a more rigorous check regime, will be sufficient to restore safety margins. They remain out of step with the European Agency, the US and the manufacturer. The update merely tells us they will continue with their work. This is a tough one - no guarantees of prevention combined with no guarantees of detection - different payers with very different opinions about the degree of risk involved in returning the aircraft to service as is.
Last edited by birmingham; 5th Feb 2017 at 16:47.
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Ferrous debris detection systems work well if engineered properly. So I think they will continue to be used for the foreseeable future.
Gouli
What you state is correct in most cases. However, the jump in vibe may occur with no meaningful time between jump an failure. Additionally, HUMS has always been basically worthless for planetaries. Early report from CAA showed it had a 70% chance of missing a problem or generating a false positive. Since then it has not improved.
Robust chip detection and crew alerts are the best bet to catch a planetary issue. If someone had taken the chips seriously REDL would not have happened.
The Sultan
What you state is correct in most cases. However, the jump in vibe may occur with no meaningful time between jump an failure. Additionally, HUMS has always been basically worthless for planetaries. Early report from CAA showed it had a 70% chance of missing a problem or generating a false positive. Since then it has not improved.
Robust chip detection and crew alerts are the best bet to catch a planetary issue. If someone had taken the chips seriously REDL would not have happened.
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The only thing that can really be taken from the AIBN statement is they haven't yet established why the fatigue occurred with a sufficient level of confidence to agree that the removal of one type of planet gear assembly and adding a more rigorous check regime, will be sufficient to restore safety margins. They remain out of step with the European Agency, the US and the manufacturer. The update merely tells us they will continue with their work. This is a tough one - no guarantees of prevention combined with no guarantees of detection - different payers with very different opinions about the degree of risk involved in returning the aircraft to service as is.
Last edited by Concentric; 6th Feb 2017 at 19:58. Reason: inserted link to official English language statement with photos
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I have been following developments in vibration monitoring for thirty years. Works great in large static machine installations, not quite so well in complex highly mobile vehicles that are subject to constantly changing external conditions.
Hindsight being a wonderful thing, I can easily envisage that certain signs were picked up in advance of the failure but not recognised for what they were because they appeared "normal", or were buried in the noise.
I am still also of the opinion that there is something different about North Sea operations compared to other areas. Whether it is weather conditions or long passages with relatively constant power settings followed by high energy manouvers to land, or some other factor, I don't have any evidence to say.
Living only a mile south of Norwich International Airport I do get to see an awful lot of helicopter movements every day. Fascinating machines, but you wouldn't get me up in one!
Hindsight being a wonderful thing, I can easily envisage that certain signs were picked up in advance of the failure but not recognised for what they were because they appeared "normal", or were buried in the noise.
I am still also of the opinion that there is something different about North Sea operations compared to other areas. Whether it is weather conditions or long passages with relatively constant power settings followed by high energy manouvers to land, or some other factor, I don't have any evidence to say.
Living only a mile south of Norwich International Airport I do get to see an awful lot of helicopter movements every day. Fascinating machines, but you wouldn't get me up in one!
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Agreed, but with the anniversary of the event approaching, it is clear they only understand "what" happened. Without a definitive answer to "why" they will be unable to provide recommendations which if implemented would make for safe travel. To still be at this stage more than nine months on is rare in my experience. Usually if the exact reason for failure cannot be found and there are no other occurrences in other units tested, investigators with follow EADS and AH's line of return to service then monitor closely. Here, because we have had two fatal incidents and they have low confidence in current advance detection methods they have held back. They say that their main investigative tool is the metallurgy and this is ongoing. Ironically part of the problem seems to be the low rate of occurrences. In all the millions of cycles as far as we know this has only happened twice. This means that the bearings are inherently very reliable. The problem, of course, is that on the two occasions when they are known to have failed it resulted in such tragic accidents.
Gouli
With 30+ years flying and operating helicopters in most parts of the oil and gas world, I disagree with you. When distance is taken into account, long range operations have basically the same flight profiles and short range have basically the same flight profiles (and HUMS readings) worldwide.
I am sure that you know that the helicopter operations on your "doorstep" is short range different, and lots of landings and take offs. Arguably, that should be the most stressful in terms of cycles and torque applications.
I am still also of the opinion that there is something different about North Sea operations compared to other areas. Whether it is weather conditions or long passages with relatively constant power settings followed by high energy manouvers to land, or some other factor, I don't have any evidence to say.
I am sure that you know that the helicopter operations on your "doorstep" is short range different, and lots of landings and take offs. Arguably, that should be the most stressful in terms of cycles and torque applications.
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Agreed, but with the anniversary of the event approaching, it is clear they only understand "what" happened. Without a definitive answer to "why" they will be unable to provide recommendations which if implemented would make for safe travel. To still be at this stage more than nine months on is rare in my experience.
If you recall, REDL happened on 1 April 2009 but the official report 2-2011 was not published until 24 November 2011, some 32 months later. That report left several loose ends. I believe the Norwegians intend to complete that unfinished business.