EC225 crash near Bergen, Norway April 2016
Join Date: Aug 2003
Location: LOS
Age: 67
Posts: 580
Likes: 0
Received 0 Likes
on
0 Posts
I have a good friend who lost about 6 feet of an S61 blade and although the result was not pretty, they all survived and the MGB/rotor head stayed attached.
I will eat crow if it is proven that the failure of one suspension bar/pin caused this, but until then I just can't believe that was the cause.
Join Date: Dec 2009
Location: Norway
Age: 49
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
Outwest : Imagine a three legged sling holding a load. If one leg(forward) breaks the load(airframe) will shift and find a new, neutural position(pitches forward). If the force holding the three legged (now two) legged sling load up(spinning rotor head) will also find a new netural position (tilts backwards). The negative dynamic stability of this configuration is dynamicly unstable and greater and greater oscillations will likely be the result.
Like I explained previously chances are that one would have the main rotor blades strike the tail. All this would happen almost instantaniously with disastrous consequences.
On top of this you will have forces such as, added drag of the airframe, the lift of the spinning rotors and blowback of the disc adding to the already hopless equation.
Loosing a part of a blade is nothing compared to loosing one of three suspension bars (not that I would like to try loosing part of a blade . . .). My chief pilot told me a story today about when one of four suspension bars on the 206LR broke many moons ago, scary stuff . . .
Like I explained previously chances are that one would have the main rotor blades strike the tail. All this would happen almost instantaniously with disastrous consequences.
On top of this you will have forces such as, added drag of the airframe, the lift of the spinning rotors and blowback of the disc adding to the already hopless equation.
Loosing a part of a blade is nothing compared to loosing one of three suspension bars (not that I would like to try loosing part of a blade . . .). My chief pilot told me a story today about when one of four suspension bars on the 206LR broke many moons ago, scary stuff . . .
Join Date: Aug 2003
Location: LOS
Age: 67
Posts: 580
Likes: 0
Received 0 Likes
on
0 Posts
Loosing a part of a blade is nothing compared to loosing one of three suspension bars
My chief pilot told me a story today about when one of four suspension bars on the 206LR broke many moons ago, scary stuff . . .
As I said before if this is proven that one suspension bar caused this I will eat crow.....but until then, I have said all I am going to on this.
Join Date: Dec 2009
Location: Norway
Age: 49
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
There is a big difference in having four vs. three bars. With four bars and a whole lot of luck one might be able to tell the story if one breaks. With three bars and one of them breaks I doubt one could 
You could just find a piece of string and try the theory by hanging something from it in a four legged sling and then cut one sling at a time and see how the load shifts. That should clarify things.
Disclaimer : I am no engineer, just a heli-driver and hobby (car)mechanic, I will stand corrected
You could just find a piece of string and try the theory by hanging something from it in a four legged sling and then cut one sling at a time and see how the load shifts. That should clarify things.
Disclaimer : I am no engineer, just a heli-driver and hobby (car)mechanic, I will stand corrected
Join Date: Aug 2004
Location: DDA
Posts: 36
Likes: 0
Received 0 Likes
on
0 Posts
In his debate about the suspension bars, the eye witness described an oscillation before the loud banging sounds (3 or 4), then parts coming off and then the rotorhead departing. What is the significance of this? Well, forces many times more than the 2.5 g (for example) that the helicopter was designed to withstand. If these oscillations were the result of a support bar or pin snapping as the possible theory would suggest, then the remaining two bars are now dealing with angular forces they are not designed for and not capable of coping with, including the mounts to the airframe. The bars are able to carry the load if the load acts in the direction of the bars and the mounts, but if you put a twisting force on them (to the magnitude of multiples of 9t) then I will guess they will fail.
In an instant.
In an instant.
Last edited by aheoe26104; 5th May 2016 at 02:17. Reason: grammer
Join Date: Nov 2002
Location: Northern Europe
Age: 45
Posts: 152
Received 0 Likes
on
0 Posts
Don't forget that light travels a lot faster than sound. Even while standing directly below the helicopter (minimum distance), the delay on the described "bangs" will be almost two seconds.
The sound the witnesses heard could easily be the start of the event, but because they were already watching the helicopter from a distance, see the results before hearing the initial event, screwing up the timeline of things.
The sound the witnesses heard could easily be the start of the event, but because they were already watching the helicopter from a distance, see the results before hearing the initial event, screwing up the timeline of things.
Join Date: Sep 2007
Location: USA
Posts: 601
Likes: 0
Received 0 Likes
on
0 Posts
The tension struts are not the only structural attachments for the MRGB. There are usually other attachments at the base of the housing. The tension struts connecting the collar at the top of the housing to the airframe are mainly used to minimize bending/distortion in the housing due to out-of-plane rotor mast moments, but they also take vertical rotor lift forces. Attachments at the housing base perimeter are used to handle in-plane rotor moments.
The tension strut arrangement is more weight efficient since it allows the housing structure to be made much lighter. Isolating the housing structure from most of the bending it would normally experience significantly reduces misalignment of gear meshes and rolling element bearing contacts.
Here is a nice photo of the tension strut and collar attachment on the H160 MRGB.
The tension strut arrangement is more weight efficient since it allows the housing structure to be made much lighter. Isolating the housing structure from most of the bending it would normally experience significantly reduces misalignment of gear meshes and rolling element bearing contacts.
Here is a nice photo of the tension strut and collar attachment on the H160 MRGB.
Join Date: Jun 2008
Location: home
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
I don't wish to deflect the discussion too much away from the accident, but there was some debate about the certification basis of the EC225 earlier in the thread.
Having worked closely with Eurocopter in 2004 and 2005 evaluating the EC225, I can categorically state that the EC225 has always been treated as a variant of the older Puma and Super Puma family. The initial EASA certification on 27 July 2004 was via a TCDS that also contained the SA330 and AS332L/L1/L2.
From a pilot licence perspective, it too has always been treated as a variant under EASA. Although if you were to speak to a CAA FOTI who was involved in the development of the Operational Suitability Data document, he would probably state that it should have been classed as a different type.
I wouldn't read too much into the lineage of certification, as it is quite common. Sikorsky have done it with the S76 family. Boeing have done it with extensively with the B737 and B747 models. At the end of the day why go to the expense of completely re-certifiying elements that were certified on a previous variant!
Having worked closely with Eurocopter in 2004 and 2005 evaluating the EC225, I can categorically state that the EC225 has always been treated as a variant of the older Puma and Super Puma family. The initial EASA certification on 27 July 2004 was via a TCDS that also contained the SA330 and AS332L/L1/L2.
From a pilot licence perspective, it too has always been treated as a variant under EASA. Although if you were to speak to a CAA FOTI who was involved in the development of the Operational Suitability Data document, he would probably state that it should have been classed as a different type.
I wouldn't read too much into the lineage of certification, as it is quite common. Sikorsky have done it with the S76 family. Boeing have done it with extensively with the B737 and B747 models. At the end of the day why go to the expense of completely re-certifiying elements that were certified on a previous variant!
Join Date: Jan 2015
Location: Europe
Posts: 111
Likes: 0
Received 0 Likes
on
0 Posts
I don't wish to deflect the discussion too much away from the accident,
Issue Date Changes
Issue 01 27 July 2004 Initial Issue; EC225LP model type certification
Issue 02 21 April 2006 Legacy Models added (SA330 and AS332)
Issue 01 27 July 2004 Initial Issue; EC225LP model type certification
Issue 02 21 April 2006 Legacy Models added (SA330 and AS332)
I wouldn't read too much into the lineage of certification, as it is quite common. Sikorsky have done it with the S76 family. Boeing have done it with extensively with the B737 and B747 models.
Anyone who treats 330/332/225 as one type should also treat it's service experience as one type (arbitrarily looking no further back than 2009, say, is just being disingenuous).
I agree. What safety factor do you think EC would have built into those suspension bars? Double, triple? Meaning that if the design gross weight is 11000 KGS how many G's of loading would they design it for? 3 G's? 4G's? Look at what Spectral has described how the 725 is operated.
Still not saying that loosing one suspension was the cause of this crash but if you would loose one suspension bar and especially if it was the longitudinal one the result would be a tilting of the rotor disc axis against the movement of the helicopter. Imagine having a chair with three legs. Guess what happens if one of those three legs brake. You end up on the floor, no matter how strong the remaining two legs are.
The only difference the strength of the remaining bars would have made in this case is that the rotor would have sliced through the rear fuselage/tail and stayed attached by the remaining two bars to the remains of the helicopter while tumbling down to Earth.
Now, why would the head shear off completely?
If the loss of the forward suspension happens at cruise speed resulting in the rotor disc tilting backwards the resulting g- load would be pretty high (up to the instantaneous Stall limit of the rotor which at 100% RRPM would surely be >>4g) and would have to be taken by only 2 remaining bars. Therefore especially losing the front suspension would very likely result in very quick separation of the whole head.
So with that in mind and knowing the load capabilities the other 2 bars must have, would a very slow decent on an a/c relatively lightly loaded have such a catastrophic failure with no warning even if and I do mean IF one bar failed?
As said that would be simply the consequence of the rotor disc axis instantly tilting to the rear (looking at the geometry of the suspension points probably ~30° from neutral) and building up massive g loads very quickly and without any chance to counter. The resulting loads on the remaining two bars would be massive and that is even without considering the rotor slicing through the fuselage/tail.
Join Date: Feb 2009
Location: A nice place
Posts: 160
Likes: 0
Received 0 Likes
on
0 Posts
Still not saying that loosing one suspension was the cause of this crash but if you would loose one suspension bar and especially if it was the longitudinal one the result would be a tilting of the rotor disc axis against the movement of the helicopter. Imagine having a chair with three legs. Guess what happens if one of those three legs brake. You end up on the floor, no matter how strong the remaining two legs are.
The only difference the strength of the remaining bars would have made in this case is that the rotor would have sliced through the rear fuselage/tail and stayed attached by the remaining two bars to the remains of the helicopter while tumbling down to Earth.
Now, why would the head shear off completely?
If the loss of the forward suspension happens at cruise speed resulting in the rotor disc tilting backwards the resulting g- load would be pretty high (up to the instantaneous Stall limit of the rotor which at 100% RRPM would surely be >>4g) and would have to be taken by only 2 remaining bars. Therefore especially losing the front suspension would very likely result in very quick separation of the whole head.
As said that would be simply the consequence of the rotor disc axis instantly tilting to the rear (looking at the geometry of the suspension points probably ~30° from neutral) and building up massive g loads very quickly and without any chance to counter. The resulting loads on the remaining two bars would be massive and that is even without considering the rotor slicing through the fuselage/tail.
The only difference the strength of the remaining bars would have made in this case is that the rotor would have sliced through the rear fuselage/tail and stayed attached by the remaining two bars to the remains of the helicopter while tumbling down to Earth.
Now, why would the head shear off completely?
If the loss of the forward suspension happens at cruise speed resulting in the rotor disc tilting backwards the resulting g- load would be pretty high (up to the instantaneous Stall limit of the rotor which at 100% RRPM would surely be >>4g) and would have to be taken by only 2 remaining bars. Therefore especially losing the front suspension would very likely result in very quick separation of the whole head.
As said that would be simply the consequence of the rotor disc axis instantly tilting to the rear (looking at the geometry of the suspension points probably ~30° from neutral) and building up massive g loads very quickly and without any chance to counter. The resulting loads on the remaining two bars would be massive and that is even without considering the rotor slicing through the fuselage/tail.
Last edited by Pablo332; 5th May 2016 at 09:14.
Thanks NF, I never thought to look at the change record!
My memory is a bit vague but there must have been a tie-up between the original EASA EC225 TCDS and the "Puma" JAR certification, as my written brief from 2005 does state that it was a variant of the AS332L and L2. Perhaps the TCDS contained a written cross-reference?
I've tried to find a copy of the original TCDS but failed.
However as discussed, it is of little consequence, other than if there are common parts or carried across design logic with previous models then once we know the root cause of this accident the ramifications could be wider than just for the EC225.
Time will tell - hopefully soon!
My memory is a bit vague but there must have been a tie-up between the original EASA EC225 TCDS and the "Puma" JAR certification, as my written brief from 2005 does state that it was a variant of the AS332L and L2. Perhaps the TCDS contained a written cross-reference?
I've tried to find a copy of the original TCDS but failed.
However as discussed, it is of little consequence, other than if there are common parts or carried across design logic with previous models then once we know the root cause of this accident the ramifications could be wider than just for the EC225.
Time will tell - hopefully soon!
Join Date: Sep 2008
Location: Croydon
Posts: 285
Likes: 0
Received 0 Likes
on
0 Posts
My answers to those questions would be...
A quick google doesn't bring anything up of any accident being caused by suspension bar failures.
Also don't confuse failures that cause accidents with secondary failures caused by accidents.
only the investigators know
They have the epicyclic in the hangar but we haven't seen any evidence to suggest they have the flared housing or the shaft that sit on top/mate into the epicyclic.