Polish HEMS Agusta 109 incident
But what's left of it is in the previous pix
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Cahsing the goose
Hi Svenstron
Thanks for the firm but polite posting. I am only to happy to acknowledge that this may be a case where the goose gets away.
I have been involved in a crash investigation on another aircraft type where it appears that the blade disbonded and the resultant loss of lift on that blade and the concurrent lift on the other blade resulted in the head tilting and the damaged rotor spar impacting the empenage. I have no firmly held position on this. All I ask is that the investigators consider my theory and if necessary dismiss it.
They may wish to look at this paper for reference on adhesive bond failure forensics:
M.J. Davis and D.A. Bond, The Importance of Failure Mode Identification in Adhesive Bonded Aircraft Structures And Repairs, 12th International Conference on Composite Materials, Paris, July 05-09 1999. If they wish to contact me I'd be only too happy to talk to them.
Regards
blakmax
Thanks for the firm but polite posting. I am only to happy to acknowledge that this may be a case where the goose gets away.
I have been involved in a crash investigation on another aircraft type where it appears that the blade disbonded and the resultant loss of lift on that blade and the concurrent lift on the other blade resulted in the head tilting and the damaged rotor spar impacting the empenage. I have no firmly held position on this. All I ask is that the investigators consider my theory and if necessary dismiss it.
They may wish to look at this paper for reference on adhesive bond failure forensics:
M.J. Davis and D.A. Bond, The Importance of Failure Mode Identification in Adhesive Bonded Aircraft Structures And Repairs, 12th International Conference on Composite Materials, Paris, July 05-09 1999. If they wish to contact me I'd be only too happy to talk to them.
Regards
blakmax
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Not hunting witches
Hi Svenstron
I assure you I have no agenda to criticise AW. I would have made the same observation if it was any company. The concentration on AW is due to the pure coincidence of the failures at DOH and Poland being on aircraft by the same manufacturer and is not of my choosing. There is certainly an element of guilt by association in my positngs because of the bonding issues I have observed on the photographs sent to me from actual disbonds from other AW139 tail booms. The characteristics there are indicative of a systemic problem associated with the integrity of their bonding processes.
Indeed I have made similar observations in relation to another manufacturer on other threads such ashttp://www.pprune.org/rotorheads/363...atalities.html
It will take a short time to inspect the blades using the Mark I eye ball to see if my suggestion is worth further investigations, because there will be fractures through the foaming adhesive used to bond the core to the spar. There may also be failures at the interface between the adhesive and ether the core or the spar. For my theory to have any relevance, there must be coincidental separation of the skin from the spar immediately adjacent to the bond failures either by disbonding or by fracture of the skin. Now it will take a few minutes to assess these conditions and all I am suggesting is that it would be worth eliminating that possibility. If my theory is not relevant in this case, only a small amount of time has been wasted. If I am right and the theory is not investigated, then there remains a risk to continuing airworthiness which could have been addressed if only a few hours of visual inspection had been expended.
Now I have in my office a section of a blade from another type which exhibits exactly the conditions I describe. In this case it was not the cause of the crash but resulted during the event. I have also a segment of a structure manufactured using similar construction methods where the same conditions led to in flight separation of a component on a fixed wing aircraft. I have also observed the conditions I describe on a number of other crashed blades. This type of failure actually does occur. Surely it is worth a few minutes of the investigators time to check this out.
With regard to the possibility that failure of the blade skin could cause such an event, if you couple a loss of lift on one blade with additional significant drag caused by the separated skin, I suggest that the resultant imbalance could cause sever loss of tracking of that blade. It may even be a driving force in setting up resonance.
I agree with you that there are other causes and it may be that one of these causes are correctly identified in this instance. Like you say, let's wait for the report.
Regards
blakmax
I assure you I have no agenda to criticise AW. I would have made the same observation if it was any company. The concentration on AW is due to the pure coincidence of the failures at DOH and Poland being on aircraft by the same manufacturer and is not of my choosing. There is certainly an element of guilt by association in my positngs because of the bonding issues I have observed on the photographs sent to me from actual disbonds from other AW139 tail booms. The characteristics there are indicative of a systemic problem associated with the integrity of their bonding processes.
Indeed I have made similar observations in relation to another manufacturer on other threads such ashttp://www.pprune.org/rotorheads/363...atalities.html
It will take a short time to inspect the blades using the Mark I eye ball to see if my suggestion is worth further investigations, because there will be fractures through the foaming adhesive used to bond the core to the spar. There may also be failures at the interface between the adhesive and ether the core or the spar. For my theory to have any relevance, there must be coincidental separation of the skin from the spar immediately adjacent to the bond failures either by disbonding or by fracture of the skin. Now it will take a few minutes to assess these conditions and all I am suggesting is that it would be worth eliminating that possibility. If my theory is not relevant in this case, only a small amount of time has been wasted. If I am right and the theory is not investigated, then there remains a risk to continuing airworthiness which could have been addressed if only a few hours of visual inspection had been expended.
Now I have in my office a section of a blade from another type which exhibits exactly the conditions I describe. In this case it was not the cause of the crash but resulted during the event. I have also a segment of a structure manufactured using similar construction methods where the same conditions led to in flight separation of a component on a fixed wing aircraft. I have also observed the conditions I describe on a number of other crashed blades. This type of failure actually does occur. Surely it is worth a few minutes of the investigators time to check this out.
With regard to the possibility that failure of the blade skin could cause such an event, if you couple a loss of lift on one blade with additional significant drag caused by the separated skin, I suggest that the resultant imbalance could cause sever loss of tracking of that blade. It may even be a driving force in setting up resonance.
I agree with you that there are other causes and it may be that one of these causes are correctly identified in this instance. Like you say, let's wait for the report.
Regards
blakmax
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After some initial speculation, I think most of us are now waiting for the official verdict. 
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Time out
Svenstron
All I have done is to alert people to a form of blade failure which happens to present itself in a form similar to that displayed on these blades and suggested that it be given a cursory assessment. I have never said definitively that this was the cause. I have alluded to bonding issues with the tail boom as an indication that there are papparently some issues involving at least part of the AW system and the photographs I posted show that this is the case.
Now put yourself in my position. I am aware of a particular failure mode which is not widely known within the investigative community. Do I raise the issue, or do I just shut up as you apparently suggest I should have done? Now if I am wrong, all that is lost is a small amount of the examiner's time. If I am right and I did shut up and the examiner missed the defect and then the same thing occurs in flight, what then?
The type of skin on the blade (composite or metal) is not an issue. The bond to which I refer is between the core and the spar, which I am sure is metal. The usual cause of failure of this bond is exposure of the core to spar foaming adhesive to high humidity.The problem with the tail boom bonds as displayed in the photos is also due to exposure of the film adhesive to high humidity. Hence the connection.
Time out. Let's wait for the report and not get too aggitated about this. Life is too short.
Regards
blakmax (there is no "c" in blakmax).
All I have done is to alert people to a form of blade failure which happens to present itself in a form similar to that displayed on these blades and suggested that it be given a cursory assessment. I have never said definitively that this was the cause. I have alluded to bonding issues with the tail boom as an indication that there are papparently some issues involving at least part of the AW system and the photographs I posted show that this is the case.
Now put yourself in my position. I am aware of a particular failure mode which is not widely known within the investigative community. Do I raise the issue, or do I just shut up as you apparently suggest I should have done? Now if I am wrong, all that is lost is a small amount of the examiner's time. If I am right and I did shut up and the examiner missed the defect and then the same thing occurs in flight, what then?
The type of skin on the blade (composite or metal) is not an issue. The bond to which I refer is between the core and the spar, which I am sure is metal. The usual cause of failure of this bond is exposure of the core to spar foaming adhesive to high humidity.The problem with the tail boom bonds as displayed in the photos is also due to exposure of the film adhesive to high humidity. Hence the connection.
Time out. Let's wait for the report and not get too aggitated about this. Life is too short.
Regards
blakmax (there is no "c" in blakmax).
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The bond to which I refer is between the core and the spar, which I am sure is metal.
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Not all things on this website should be treated as facts!
No not at all....
but:
2005. from some CAA Bulletins
ROTOR&RESCUE 2006/2007
for me strong indication that metal parts are there...
(Because of well known reasons must use data from public sources only......)
but:
2005. from some CAA Bulletins
Several cases of main rotor blade cracking have been found in service, including one which failed catastrophically. Fatigue cracking has been initiated by chordwise scoring, introduced during manufacture, adjacent to spar mass balance weights.
– The rotor blades, made of composite materials,have what Agusta
describes as a “vibration reducing mass distribution along the M/R blade span”.
This new design allowed removing the little spoilers typical for AgustaWestland’s
rotorblades, and drawing a new aerodynamic profile of the blade roots that significantly reduces the rotor’s drag.
describes as a “vibration reducing mass distribution along the M/R blade span”.
This new design allowed removing the little spoilers typical for AgustaWestland’s
rotorblades, and drawing a new aerodynamic profile of the blade roots that significantly reduces the rotor’s drag.
(Because of well known reasons must use data from public sources only......)
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All I can say is: My A109E type conversion technical notes "workbook" (written by the Agusta factory training center) state:
*root - my edit. Everything else copied verbatim.
Other A109 models are different.
Blades are made of composite: the blade consists of a 'D' shaped composite spar and the trailing edge is made of nomex core and carbon fibre skins. Blade aerofoils at the root are of the high lift type (AG8021).
Blade airfoils at the tip are of the high velocity type (AG8026).
The leading edge is protected against wear by a bonded stainless steel abrasion strip. Each blade has a bendable trailing edge trim tab adjustable for rotor dynamic tracking. The blades are designed with a "droop snoot" airfoil section and the thickness is tapered from rotor (root*) to tip to optimize the lift coefficient, the blade pitch range and to reduce noise level.
The composite main rotor blades due to the static balancing of each blade to a master blade as a final manufacturing process, they are completely interchangeable.
Blade airfoils at the tip are of the high velocity type (AG8026).
The leading edge is protected against wear by a bonded stainless steel abrasion strip. Each blade has a bendable trailing edge trim tab adjustable for rotor dynamic tracking. The blades are designed with a "droop snoot" airfoil section and the thickness is tapered from rotor (root*) to tip to optimize the lift coefficient, the blade pitch range and to reduce noise level.
The composite main rotor blades due to the static balancing of each blade to a master blade as a final manufacturing process, they are completely interchangeable.
Other A109 models are different.
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This raises a question of terminology which has bugged me for years. The FAA discusses "composites" meaning both composite construction where a structure is fabricated from details (fibre composite or metal) which are bonded together and they also use the same term for fibre composites. (See AC20-107B) I would be surprised if EASA and many OEMs did not have the same mixed terminology. I personally prefer to reserve the word composite to mean fibre composites and describe structure made up of bonded details as bonded structure. No confusion.
If my theory is correct, the only difference the spar material will make is the visible part of the back of the spar will be black for composite or metallic for the alternative materials. Irrespective of the material actually used to make the spar, the strength of the bond should always be greater than the strength of the core. Hence, if there is core still attached to the rear of the spar, then my theory is not applicable, move on. If however the bond to the rear of the spar was weaker than the strength of the core, there will be an absence of core residue at the rear of the spar and there may be a problem. A simple five minute look at the rear of the spar is all that is initially required.
Circular/fragmented arguement. Wait for the report.
If my theory is correct, the only difference the spar material will make is the visible part of the back of the spar will be black for composite or metallic for the alternative materials. Irrespective of the material actually used to make the spar, the strength of the bond should always be greater than the strength of the core. Hence, if there is core still attached to the rear of the spar, then my theory is not applicable, move on. If however the bond to the rear of the spar was weaker than the strength of the core, there will be an absence of core residue at the rear of the spar and there may be a problem. A simple five minute look at the rear of the spar is all that is initially required.
Circular/fragmented arguement. Wait for the report.
Last edited by blakmax; 3rd Dec 2009 at 20:11. Reason: typo
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My final observation is that (from the larger photo) the damaged blades seem to have the top skin broken / smashed off the spar, rather than disbonded from it. You can see the line of the spar near the tip of the near blade.
Good idea.
Wait for the report.
Agusta Blades: Just so there's no doubts left folks, Agusta use different blades on the 109 series. The A109A/AII use the 109 series blade that are of metal construction. The 109C series onwards (C, E, K, K2, S etc & the 119) all use the 709 series blades that are of composite construction (including the spar) but of course have the metal leading edge strip bonded on to fight against erosion. I doubt that debonding of one of these blades was the cause of this incident but I'll stand corrected.
Safe flying
R2
Safe flying
R2