I just hope I'm not sitting
In 6 months time reading an accident report stating that HUMS data indicated a trend 3 days before the accident.

OK, looking at the pictures etc.

If the vertical 'lift' loads are taken by the 3 rods, how does the gearbox failing cause the rotor head to break away?

What exactly is on the airframe end of the rods?

Are these 2 strut rods maybe the same component ?

http://i86.servimg.com/u/f86/11/94/64/62/hub7b10.jpg

http://i86.servimg.com/u/f86/11/94/64/62/hub910.jpg

The separation point must be below the green bolts since we can se the suspension bar on the picture.

One strut rod by the red arrow(suspension bar),and one pitch link(with black tape) i think.

So if we can see the swashplate, the likely separation point is at the row of green bolts underneath. (where the struts attach)

Not very likely , not a lot going on here unless you install barrel nuts upside down.

Next MGB joint is to the ring gear of the epicyclic reduction gear, lots going on here.

After looking at the end of the suspension bar we can see with the pictures available Pin/washer and securing pins could be intact.

The MRB leading edge protective covering shows buckling approx. 1/3 from root which may have been caused by excessive bending of the spar due to excessive pitch.

It may well do, but that's not the same as suggesting HUMS should have a real time involvement in decision making.

Pablo, so you think the separation point is the row of bolts at the bottom of the diagram? (grey casing)

The ring gear has a bit of previous on this type of helicopter.

At the moment all is speculation.

Some similarities to G-AWAP
 

Take a look at the AAIB report for G-AWAP lost in 1983 off Norfolk coast.

The report concludes that the accident was caused by the disengagement of the main rotor head retention bolt, with consequential detachment of the rotor, due to corrosion of the engaging threads between it and the mast.

Not to say this was the case but as an inspection engineer that regularly flew in G-AWAP and took an interest in her fate, I was struck by the recent video and the eyewitness reports of G-AWAP, a loud crack and a detached rotor landing away from the main wreck.

https://assets.digital.cabinet-office.gov.uk/media/5422ed76e5274a1317000199/3-1985_G-AWAP.pdf

Am I right in saying that the material failure of the planet gear G –REDL is still unexplained by the manufacturer?

https://assets.digital.cabinet-offic...REDL_08-09.pdf

The initial examination of the wreckage, in conjunction
with radar, HUMS, CVFDR and witness data,
determined that a failure within the epicyclic reduction
gearbox module of the MRG resulted in the rupture of
the gearbox case. This allowed the main rotor head,
together with the upper section of the MRG, to separate
from the helicopter.

Does anyone have an illustration showing the lower attachment points of the strut rods?

Just a slight impostor here but reading this and other accidents the MGB sudden seizure tears the whole assembly out of the top?

If so is there any way of making a shear ring that would fail but leave the blades attached ?

I know it's a wild stab in the dark but there appears to be no redundancy if it fails.

Like the old safe life on fixed wing structures .

What to do pilots?/Help us!
 

Offshore workers feel let down-what is happening with this aircraft? For many people its stick or bust time.
Transit to and from offshore is becoming a gamble and in a professional environment it should not be thus.

Workplace health and safety. Your Union should be involved with your employer. Follow the reg's. I'm sure even the 225 pilots are concerned.

VG.NO (Norwegian Newspaper) is now reporting that LN-OJF made a RTB on Tuesday, 16 minutes into a flight, due to a Warning Light (not specified). On Wednesday an engine part was changed and a short local test flight was made. The same Warning Light appeared once again (still not specified), and yet another engine part was changed. Another test flight was then performed. This time everything appeared to be OK. LN-OJF then performed six commercial flights on Thursday without remarks.

The alternative is transfer by boat and lifting men on and off the rigs by crane. Would that be safer than helicopters? I doubt it.

As this was a Statoil contract the HUMS data would have been checked between flights.
In fact after this was put into the Statoil contract (several years ago) CHC check all HUMS data between flights.

Condolences to the families of the crew and passengers - so many people hurt & directly affected

Frightening footage! The forum with discussions and theories of the cause is interesting and some of you obviously have a high level of technical knowledge however regardless of what is determined as the cause and any potential flaws with the IHUMS or the procedure of downloading and interpreting the information, the damage is done and the confidence, whether warranted or not, seems to be lost in the EC25.

Any shortfalls in procedures should of course be addressed appropriately but especially in today's environment it wouldn't want to cost too much. Affordable safety in world of greed. Sorry a cynical view I know but some of you may share my view.

There was an initial report of fire before the separation. Now statements that engine parts were changed in the days before the crash. Is there an escalation path from an engine 'issue' to separation of the rotor head?

I think if the MGB was undergoing the process of self destruction, with all that heat and oil, as soon as the case cracked it is quite feasible that oil ignition would be likely.

HUMS as an on-board tool
 

A newbie on this site, but interested in rotorcraft safety for sometime.
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)?

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.

Altimus

All oil and gas contracted 225s are fitted with the redesigned bevel gear shaft.

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.

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.

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.

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.

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??

Hi Mitchaa

I think the MD 902 is similar with the gearbox slung under a frame on top of the transmission deck.

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.

Rotorhead recovered:
Bergensavisen - Det vil ta dager før de svarte boksene kan åpnes

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

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.

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.

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'm sure he meant April instead of March Mitchaa! easily done...:ugh:

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

House of Commons - Offshore helicopter Safety - 2014
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?

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.