EC225 crash near Bergen, Norway April 2016
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HUMS as an on-board tool
Anyone who thinks HUMS data could be interpreted in real time has never seen the Data before. Please stop thinking HUMs is a magic tool to determine maintenance requirements. HUMs has always been and still is a maintenance TOOL. Not a determining factor nor reliable enough to make a decision such as ditching a Helicopter as some seem to think or those in suits want everyone to believe. Some HUMS indications are so vague it can take a LONG time to determine if the HUMs system or aircraft is faulty. Much longer than your typical out and back trip offshore helicopters take making real time impossible. Whatever failed on this Helicopter happened incredibly fast. Faster than even the Pilots onboard to realize something was wrong. HUMs=USELESS in that situation. If the data is still intact on the card then it may help investigators determine what failed easier.
I agree in principle that HUMS indications are generally vague, need to be analyzed in the right statistical context, and, from the operational perspective, can result in an unacceptably high false positive rate. As a result, they are generally not expected to be used on-line on-board at their current level of maturity.
However, I am reading the Aircraft Accident Report for G-REDW and G-HCN from 2/2014
https://www.gov.uk/aaib-reports/aar-...cn-10-may-2012
As a reminder, two ditchings in 2012 were caused by fatigue cracks in bevel gear vertical shaft. One of the findings of that report was that original finite element analysis (FEA) used for certification of EC225 underpredicted the stresses in the bevel gear vertical shaft by a factor of 3.8 (page 98). As a result, the estimated safety margin was reduced from 5.4 to 2.1 (page 152), which basically invalidated the original certification (for the safety margin under 3, FEA alone would not sufficient and fatigue test would be required).
At the same the relevant HUMS indicators, and MOD45 in particular seemed to provide an early warning, but only about two-to-four hours in advance (this is my interpretation rather than how it was stated in the report, but take a look at Figures 22 and 23 of the report).
So, one of the recommendations of that report has led to ASB No EC225-45A010 ‘Central Maintenance System – HUMS – M’ARMS MOD45 on-board monitoring system’, dated 8 July 2013. I quote: "The purpose of this ASB was to upgrade the MFDAU (Miscellaneous Flight Data Acquisition Unit) software to:
● Calculate the MOD-45 indicator in real time.
● Increase the acquisition rate.
● Display the MOD-45 indicator status on the HUMS Control Panel or (Man-Machine Interface)"
I tracked ASB No EC225-45A010 document to the most current AD No.: 2014-0078R1 from July 08, 2014. The best I could tell from this last document is that the recommendation was indeed implemented for some rotorcraft, but there was another option:
"after EASA AD 2014-0078 was issued, Airbus Helicopters redesigned the MGB bevel gear vertical shaft through modification MOD 0752525, which provides new nitrided shaft P/N 332A32-5109-00/01/05/06. This new shaft design eliminates a possibility of mechanical failure of the shaft. However incorporation of the new shaft requires to keep previous installation of a new MGB oil jet (MOD 0753021), and is incompatible with M’ARMS MOD45 monitoring function (MODs 0726994 and MOD 0728083) as initially required for EC 225 helicopters equipped with a VHM"
In summary, while it might be unwise to rely on HUMS for safety warnings on board, the Aircraft Accident Report has recommended to do just that. Two questions:
1. Is it possible from the evidence we have so far to rule out the possibility that this current accident was caused by bevel gear vertical shaft failure?
2. Was this specific rotorcraft equipped with M’ARMS MOD45 monitoring function or had a redesigned MGB bevel gear vertical shaft that "eliminates a possibility of mechanical failure of the shaft" (or neither)?
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Support??
Does anyone else think that the "strut" poking up in the picture looks more like the control rod that connects to the MR servos than the gearbox support beams? It looks too thin, and wrong type of ends/bearing.
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Altimus
All oil and gas contracted 225s are fitted with the redesigned bevel gear shaft.
2. Was this specific rotorcraft equipped with M’ARMS MOD45 monitoring function or had a redesigned MGB bevel gear vertical shaft that "eliminates a possibility of mechanical failure of the shaft" (or neither)?
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From the pictures posted of the rotor remains, it appears the structural failure occurred in the upper section of the gearbox housing. All of the rotor system from the swashplate up separated from the airframe.
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As Mitchaa said; "I'm a betting man " and I think this accident has nothing to do with MGB failure.
Watch out the G-REDL - MRH, mast with swashplate, flared housing with one suspension bar still attached to it - picture in post 145.
Do you see a difference between the end of the suspension bar on that picture and the one on picture in post 172 ?
While this suspension bar is supposed to be bolted to a fitting bolted on the fuselage, the one in post 172 looks un-damaged. I would really like to see the other face of this suspension bar.
Watch out the G-REDL - MRH, mast with swashplate, flared housing with one suspension bar still attached to it - picture in post 145.
Do you see a difference between the end of the suspension bar on that picture and the one on picture in post 172 ?
While this suspension bar is supposed to be bolted to a fitting bolted on the fuselage, the one in post 172 looks un-damaged. I would really like to see the other face of this suspension bar.
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Hear what you say TenTon, but surely it's just a matter of time, albeit a few years, before HUMS info is indeed analysed - at least in part - in real time and cockpit warnings are provided for the most serious anomalies. But maybe this already happens to an extent? Also be interesting if the CVR picked up any observations from the most basic HUMS device - the crew - of any increase in vibration levels before failure.
Aircraft have been flying since the 60's with a separated head/main gearbox i.e the Hughes 300/500 series. In the case of the 500 the gearbox is slung below the structure it drives a shaft through a hollow mast to the head which attaches to the shaft by bolts and to the mast by a nut.
In theory the main gearbox could fall out of the aircraft and the rotors and flying controls would operate normally. It is normal to remove a 500 gearbox without disturbing the rotor or flying controls.A gearbox seizure would result in the lower part of the drive shaft shearing at a shear point but the head and control would still remain functional attached to the mast.
However a failure of the mast or the thrust bearing in the head would still result in loss of the aircraft.
In theory the main gearbox could fall out of the aircraft and the rotors and flying controls would operate normally. It is normal to remove a 500 gearbox without disturbing the rotor or flying controls.A gearbox seizure would result in the lower part of the drive shaft shearing at a shear point but the head and control would still remain functional attached to the mast.
However a failure of the mast or the thrust bearing in the head would still result in loss of the aircraft.
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Mitchaa
It looks to me like the Suspension Bar pin is still installed and if you look really closely the airframe mounting has actually sheared and part of it is still attached between the forks.
It looks to me like the Suspension Bar pin is still installed and if you look really closely the airframe mounting has actually sheared and part of it is still attached between the forks.
There are a number of single point failures on all helicopters - I would say that they are always well 'over-engineered' but the gearbox / rotorhead mounting design of the Puma family has always looked surprisingly weak, whilst history and shear number of hours flown has proven this as a very effective design.
As to live HUMS data, the problem has always been that the systems themselves are considerably more reliable than the sensors, micro-switches and telemetry of a HUMS set-up. Do we want to be flagging warning lights in the cockpit at the rate that engineers will see spikes on the HUMS print-out??
As to live HUMS data, the problem has always been that the systems themselves are considerably more reliable than the sensors, micro-switches and telemetry of a HUMS set-up. Do we want to be flagging warning lights in the cockpit at the rate that engineers will see spikes on the HUMS print-out??
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To have that amount of "intact" evidence will hopefully help to determine the primary cause quickly.
There are only 2 primary cause possibilities in my opinion, another epicyclic module failure or maintenance error. Of course, if its epicyclic failure, there will be dozens of contributing factors to analyze, HUMS, monitoring, gear manufacture, just like REDL.
If its an MGB failure, I think the 225 is finished for offshore use. The Eurocopter re-branding to Airbus Helicopters to distance itself from the 2x NS ditching accidents may prove to tarnish more than polish the Airbus name. It will certainly advertise deep pockets for the lawyers who will represent the poor families affected by this tragedy.
If its a maintenance error, the 225 will survive. Whichever is the cause, the fallout will be very difficult to bear.
CHC could end up as being simple collateral damage caused by no revenue being generated by the 225. Oil and gas companies won't pay again for an extended grounding.
My positive thoughts are with everyone, I am genuinely very saddened by this.
There are only 2 primary cause possibilities in my opinion, another epicyclic module failure or maintenance error. Of course, if its epicyclic failure, there will be dozens of contributing factors to analyze, HUMS, monitoring, gear manufacture, just like REDL.
If its an MGB failure, I think the 225 is finished for offshore use. The Eurocopter re-branding to Airbus Helicopters to distance itself from the 2x NS ditching accidents may prove to tarnish more than polish the Airbus name. It will certainly advertise deep pockets for the lawyers who will represent the poor families affected by this tragedy.
If its a maintenance error, the 225 will survive. Whichever is the cause, the fallout will be very difficult to bear.
CHC could end up as being simple collateral damage caused by no revenue being generated by the 225. Oil and gas companies won't pay again for an extended grounding.
My positive thoughts are with everyone, I am genuinely very saddened by this.
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Rotorhead recovered:
Bergensavisen - Det vil ta dager før de svarte boksene kan åpnes
Bergensavisen - Det vil ta dager før de svarte boksene kan åpnes
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The Strut Rod in the picture is a suspension bar. The suspension bar is secured to the airframe with a Pin not a bolt and nut. The pin is secured with 2 nappy pins and a washer, from the resolution of the pictures I’m not sure these items are missing.
that MGB shaft looks pretty intact in that underslung load shot..
The whole shaft has come out of the gearbox... Catastrophic engine or input shaft failure followed by MGB destruction? as in LN-OPG
http://www.aibn.no/ln_opg_eng_total-...-File&attach=1
The whole shaft has come out of the gearbox... Catastrophic engine or input shaft failure followed by MGB destruction? as in LN-OPG
http://www.aibn.no/ln_opg_eng_total-...-File&attach=1
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As for basket transfers, most companies consider this much more dangerous then any heli transfer.
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http://http://www.bt.no/nyheter/loka...l#&gid=1&pid=1
If you zoom in, screenshot , and zoom once more, you can actually see tht the bolt is missing from the suspebnsion bar (airframe side). It looks like the pin is installed and that there is a fitting attached to it, but it is actually a peace of grass.
If you zoom in, screenshot , and zoom once more, you can actually see tht the bolt is missing from the suspebnsion bar (airframe side). It looks like the pin is installed and that there is a fitting attached to it, but it is actually a peace of grass.
Various reports state (and I can't swear to the accuracy, but I think I've seen it enough that it is confirmed) that the gearbox was changed on January 17th and the rotorhead on March 27th - 2 days before the accident.
I believe that apart from a couple of short maintenance flights, this was the first full passenger flight since the rotorhead change. I would imagine that will be the focus of the investigation right now.
The one witness statement that made me think possible gearbox failure / seizure was a comment that the in addition to the strange noise and a bang, the helicopter was seen to rotate in the air before an explosion, but this could be just about anything and may have been post rotor detachment.
Either way, witnesses on the ground seem to have been drawn to look up, film, look for the aircraft due to a strange noise, at least several seconds before the crash, so it suggests (in some ways similar to BND85N) that there was a short period of intense noise and gearbox stress before breakup.
Terrible tragedy. If this is an engineering / maintenance issue (and that is an 'if', the aircraft could be signed back to fly fairly quickly. Whether the passengers would accept it is another matter?
I believe that apart from a couple of short maintenance flights, this was the first full passenger flight since the rotorhead change. I would imagine that will be the focus of the investigation right now.
The one witness statement that made me think possible gearbox failure / seizure was a comment that the in addition to the strange noise and a bang, the helicopter was seen to rotate in the air before an explosion, but this could be just about anything and may have been post rotor detachment.
Either way, witnesses on the ground seem to have been drawn to look up, film, look for the aircraft due to a strange noise, at least several seconds before the crash, so it suggests (in some ways similar to BND85N) that there was a short period of intense noise and gearbox stress before breakup.
Terrible tragedy. If this is an engineering / maintenance issue (and that is an 'if', the aircraft could be signed back to fly fairly quickly. Whether the passengers would accept it is another matter?
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I'm sure he meant April instead of March Mitchaa! easily done...
Special 25, I can't see the 225 flying again certainly not in the North Sea. Confidence is certainly at rock bottom & it took a long time for confidence to be built up again after the last accidents/controlled ditching's relating to gearbox issues in the North Sea (including L2) which wasn't that long ago as we all know. Far too many.
You just have to look back at the chinook crash in the late 80's just off Sumburgh. They were quickly taken out of service in the North Sea.
Talking of L2, I believe Bond have grounded them now too. Wise move.
After seeing that video of the rotor head assembly with blades spinning down to the ground certainly made me speechless. Very horrible & sad to see.
I feel for all the families involved & staff at CHC.. worrying times ahead
Special 25, I can't see the 225 flying again certainly not in the North Sea. Confidence is certainly at rock bottom & it took a long time for confidence to be built up again after the last accidents/controlled ditching's relating to gearbox issues in the North Sea (including L2) which wasn't that long ago as we all know. Far too many.
You just have to look back at the chinook crash in the late 80's just off Sumburgh. They were quickly taken out of service in the North Sea.
Talking of L2, I believe Bond have grounded them now too. Wise move.
After seeing that video of the rotor head assembly with blades spinning down to the ground certainly made me speechless. Very horrible & sad to see.
I feel for all the families involved & staff at CHC.. worrying times ahead
Pozidrive, the alternative desired isn't transfer by boat, but a different helicopter. People are spooked, and I do think oil workers and oil companies are concerned about the 225 and regardless of statistics, its going to take a lot to convince some people that this aircraft is safe. I am also sure that HSE Managers worldwide will be looking closely at the risks associated with this aircraft.
As for basket transfers, most companies consider this much more dangerous then any heli transfer.
As for basket transfers, most companies consider this much more dangerous then any heli transfer.
http://www.publications.parliament.u...an/289/289.pdf
(Page 11 for accident rates 1976-2013.)
- Super Puma variants accounted for 60% of the NS fleet:unsurprising that they are involved in more accidents
- Confidence rates in ALL models of large/heavy helicopter less than 50%.
- Why were these accidents all in the UK sector and none in Norway?
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There is no reason so far to believe that this accident is not a repeat of the G-REDL incident. I was not very satisfied with the report on this accident as it struck me as being complacent, that just to keep on doing the same things, but better was going to prevent the same thing happening again.
In the repotr it was said:-
"Safety Recommendation 2011-036 It is recommended that the European Aviation Safety Agency (EASA) re-evaluate the continued airworthiness of the main rotor gearbox fitted to the AS332 L2 and EC225 helicopters to ensure that it satisfies the requirements of Certification Specification (CS) 29.571 and EASA Notice of Proposed Amendment 2010-06."
Was this done?
The report contains the following passage:-
"Epicyclic gearbox spalling events on the AS332 L2 helicopter Data provided by the helicopter manufacturer indicated that between 2001 and 2009 there were nine recorded cases of planet gear spalling on the AS332 L2 (see Table 2). In addition, information provided by the operator showed that there had been seven events in 2010 on their fleet where magnetic particles had been found on the MGB magnetic chip detectors which had resulted in the removal of the gearbox for repair. The information provided by the manufacturer regarding the number of planet gear rejections due to spalling was incomplete. During the investigation anecdotal evidence was provided that indicated that overhaul facilities disposed of rejected gears without routing them for investigation."
This indicates to me a high level of complacency, the kind that brought down two NASA shuttles. Bearing spalling is not something you ever want to see in a gearbox, as it's progression is not predictable and often results in rolling elements being deposited into the gear mesh. At which point it is game over for the gearbox.
In the repotr it was said:-
"Safety Recommendation 2011-036 It is recommended that the European Aviation Safety Agency (EASA) re-evaluate the continued airworthiness of the main rotor gearbox fitted to the AS332 L2 and EC225 helicopters to ensure that it satisfies the requirements of Certification Specification (CS) 29.571 and EASA Notice of Proposed Amendment 2010-06."
Was this done?
The report contains the following passage:-
"Epicyclic gearbox spalling events on the AS332 L2 helicopter Data provided by the helicopter manufacturer indicated that between 2001 and 2009 there were nine recorded cases of planet gear spalling on the AS332 L2 (see Table 2). In addition, information provided by the operator showed that there had been seven events in 2010 on their fleet where magnetic particles had been found on the MGB magnetic chip detectors which had resulted in the removal of the gearbox for repair. The information provided by the manufacturer regarding the number of planet gear rejections due to spalling was incomplete. During the investigation anecdotal evidence was provided that indicated that overhaul facilities disposed of rejected gears without routing them for investigation."
This indicates to me a high level of complacency, the kind that brought down two NASA shuttles. Bearing spalling is not something you ever want to see in a gearbox, as it's progression is not predictable and often results in rolling elements being deposited into the gear mesh. At which point it is game over for the gearbox.