AW139 lost tail taxying DOH
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blakmax, thanks for your erudite and informed contributions. Reading your posts one could come to the conclusion that little is known in certain segments of the industry about bonding (Your quote "It is still a processing problem"). I would have thought that the industry would have extensive hands on experience and be mature with little left to learn, with the development of Redux bonding occurring back in 1941. First use on a all metal aircraft was the DH Dove (1945) I think, and used extensively on the DH Comet (1949). The importance of surface treatment of aluminium was well appreciated during the early Redux development period. Am I missing something?
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responses (late at night down under)
Ok, I'll try to respond as rapidly as the messages come in, but soon I must snoo!
Firstly, it is not the wash fluid which are the problem. It is the persistence of humidity, combined with temperature. Remember that higher humidity simply accelerates the problem for a deficient interface. It is a moisture diffusion problem, not a moisture flooding problem. A durable interface is resistant to any hydration mechanism, be it wash fluids or humidity.
Secondly, the major difference between Redux bonding and current processes is that the Redux adhesives were phenolic based and they had a strong acid-base reaction which produced durable bonds. My understanding is that current epoxy adhesives do not exhibit as strong an acid-base reaction and hence they rely on the chemical activity generated by processing of the surfaces. They are therefore more susceptible to hydration, so treatment must address hydration reistance.
Why don't we change back to phenolic adhesives? Because they are condensation polymerisers which produce water as a by-product of the reaction. That water leads to micro-voiding as that water turns to steam during the cure cycle, which results in micro-voiding which reduces the bond strength. Don't be fooled by thinking that vacuum draws such volatiles out; in reality vacuum reduces the pressure and therefore makes the bubbles larger. It is the adhesive which is drawn out, not the volatiles. In contrast, epoxies are addition polymerisers, and they do not produce water as a by-product and hence they are less susceptible to micro-voiding. But the interfacial reactions are more dependent on the chemical activity of the surface and the resistance to hydration.
Now to my favourite subject: Quality. Almost every manufacturer currently uses Quality Assurance (QA) testing to verify structural integrity. Indeed, there are regulatory requirements that are directed towards QA. As already stated, strength tests only produce a snap-shot of current strength. So if the test is conducted before the interface has had time and humidity to hydrate, a false positive result occurs. If combined with NDI (which can not interrogate the interface) then one has a warm, fuzzy feeling that the product is structurally sound. In some cases, such products have an absolute certainty that they will fail in service. Again, I stress that such products can actually demonstrate compliance with the regulations (FAR, JAR, DEF STAN 00 970 etc.)
The problem with QA is that it is nothing more than a "leave pass". If you can meet the requirements of selected tests (usually strength tests based on coupon samples cured with the part) and if it passes NDI, then it is an approved part and you get the weekend off. IT DOES NOT MATTERWHAT YOU DO TO GET THAT LEAVE PASS.
In contrast, there is a far better way of managing quality, and that is Quality Management (QM). In this process, every step of the process is firstly validated using tests that guarantee bond integrity and importantly guarantee bond hydration resistance. Process specifications must match exactly those validated processeses. Then the easy bit. Just make sure it is correctly implemented by certification of compliance with validated process specifications by competent technicians using approved materials that have been correctly handled and exposed in only a controlled environment and using equipment that is appropriate to the task..
Recognise that you can inspect a product and test coupons all you like. You will NEVER change the quality of the product. Manage the quality and it will pass every test you throw at it. And it will actually be a quality product which should not fail in the manners described in this thread.
How can I be so confident? These principles reduced the repeat repair rate for bonded repairs from 43% in 1992 to three bond failures since then, and every one of those could be tracked to technician error or laziness.
We do not have an engineering problem; we have an education problem.
Regards
blakmax
PS If you contact me by PM, blakmax has no "c" in it. We convicts down under can't spell.
PPS SASless. You can take a weekend off after this! Put your feet up, old chap! :-)} (The additional } is because I have a beard. Never did understand why grown men scratch the hair off their face so they look like women!)
Firstly, it is not the wash fluid which are the problem. It is the persistence of humidity, combined with temperature. Remember that higher humidity simply accelerates the problem for a deficient interface. It is a moisture diffusion problem, not a moisture flooding problem. A durable interface is resistant to any hydration mechanism, be it wash fluids or humidity.
Secondly, the major difference between Redux bonding and current processes is that the Redux adhesives were phenolic based and they had a strong acid-base reaction which produced durable bonds. My understanding is that current epoxy adhesives do not exhibit as strong an acid-base reaction and hence they rely on the chemical activity generated by processing of the surfaces. They are therefore more susceptible to hydration, so treatment must address hydration reistance.
Why don't we change back to phenolic adhesives? Because they are condensation polymerisers which produce water as a by-product of the reaction. That water leads to micro-voiding as that water turns to steam during the cure cycle, which results in micro-voiding which reduces the bond strength. Don't be fooled by thinking that vacuum draws such volatiles out; in reality vacuum reduces the pressure and therefore makes the bubbles larger. It is the adhesive which is drawn out, not the volatiles. In contrast, epoxies are addition polymerisers, and they do not produce water as a by-product and hence they are less susceptible to micro-voiding. But the interfacial reactions are more dependent on the chemical activity of the surface and the resistance to hydration.
Now to my favourite subject: Quality. Almost every manufacturer currently uses Quality Assurance (QA) testing to verify structural integrity. Indeed, there are regulatory requirements that are directed towards QA. As already stated, strength tests only produce a snap-shot of current strength. So if the test is conducted before the interface has had time and humidity to hydrate, a false positive result occurs. If combined with NDI (which can not interrogate the interface) then one has a warm, fuzzy feeling that the product is structurally sound. In some cases, such products have an absolute certainty that they will fail in service. Again, I stress that such products can actually demonstrate compliance with the regulations (FAR, JAR, DEF STAN 00 970 etc.)
The problem with QA is that it is nothing more than a "leave pass". If you can meet the requirements of selected tests (usually strength tests based on coupon samples cured with the part) and if it passes NDI, then it is an approved part and you get the weekend off. IT DOES NOT MATTERWHAT YOU DO TO GET THAT LEAVE PASS.
In contrast, there is a far better way of managing quality, and that is Quality Management (QM). In this process, every step of the process is firstly validated using tests that guarantee bond integrity and importantly guarantee bond hydration resistance. Process specifications must match exactly those validated processeses. Then the easy bit. Just make sure it is correctly implemented by certification of compliance with validated process specifications by competent technicians using approved materials that have been correctly handled and exposed in only a controlled environment and using equipment that is appropriate to the task..
Recognise that you can inspect a product and test coupons all you like. You will NEVER change the quality of the product. Manage the quality and it will pass every test you throw at it. And it will actually be a quality product which should not fail in the manners described in this thread.
How can I be so confident? These principles reduced the repeat repair rate for bonded repairs from 43% in 1992 to three bond failures since then, and every one of those could be tracked to technician error or laziness.
We do not have an engineering problem; we have an education problem.
Regards
blakmax
PS If you contact me by PM, blakmax has no "c" in it. We convicts down under can't spell.
PPS SASless. You can take a weekend off after this! Put your feet up, old chap! :-)} (The additional } is because I have a beard. Never did understand why grown men scratch the hair off their face so they look like women!)
Last edited by blakmax; 2nd Sep 2009 at 13:35. Reason: told you we convicts can't spell
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Wrote a thoroughly boring paper for a supply chain management course on essentially this very subject. The operation in question was a small composites shop manufacturing generally small aircraft panels.
Their longer-term goal is to get into becoming a key supplier for major aircraft OEMs.
We initially found their waste to be rather high. We then found that their rejected parts rate was high. Working backward through the process, we discovered that their clean room processes weren't particularly well controlled, nor were their quality functions managed. We then found that their sourcing for such items as prepreg and honeycomb was large, infrequent lots (this is bad because these items have a shelf life, even when properly stored) resulting in either waste or usage of expired materials.
There were other issues, but in short, they would be unable to become a key supplier for a ISO 9001 customer (which most major aerospace manufacturers are... though having read this thread I begin to wonder if Agusta is) without changing basically every aspect of their supply chain, from procurement through quality.
As I read blakmax's posts, I get the sense that there is a lot of variability in the quality of production in these parts, to include voiding, moisture, improper curing, and whatever other problems can arise in the process. I would think any of these would make the final product unstable with regard to widely varying environmental conditions.
So, yes, blakmax... I think quality may be the thing to be attacked. I've learned a great deal reading your posts. Thanks for that.
Their longer-term goal is to get into becoming a key supplier for major aircraft OEMs.
We initially found their waste to be rather high. We then found that their rejected parts rate was high. Working backward through the process, we discovered that their clean room processes weren't particularly well controlled, nor were their quality functions managed. We then found that their sourcing for such items as prepreg and honeycomb was large, infrequent lots (this is bad because these items have a shelf life, even when properly stored) resulting in either waste or usage of expired materials.
There were other issues, but in short, they would be unable to become a key supplier for a ISO 9001 customer (which most major aerospace manufacturers are... though having read this thread I begin to wonder if Agusta is) without changing basically every aspect of their supply chain, from procurement through quality.
As I read blakmax's posts, I get the sense that there is a lot of variability in the quality of production in these parts, to include voiding, moisture, improper curing, and whatever other problems can arise in the process. I would think any of these would make the final product unstable with regard to widely varying environmental conditions.
So, yes, blakmax... I think quality may be the thing to be attacked. I've learned a great deal reading your posts. Thanks for that.
I have always thought that ISO9001 was a recipe for disaster, have read lots of manuals, from war and peace to concise & to the point ones.
The problem is if it was wrong in the first place it is then a struggle to rectify, as long as you do it by the manual it must be OK, yes I know you have updates, revisions but the No. of companies that consistently get it wrong suggests there must be a better way.
Some consultants write a large part of them with no in depth understanding of the business they are writing for.
blakmax
Interesting to hear your thoughts of vacuum causing larger voids, we have used to remove excess resins & entrapped air rather than vapours, but I can follow the argument regarding humidity, something else to factor into the equation.
How would you guard against volatiles entrapment other than slow cure and super critical mixes ?
PS
I only scrape small portion of skin is this in keeping with the rugged down under
The problem is if it was wrong in the first place it is then a struggle to rectify, as long as you do it by the manual it must be OK, yes I know you have updates, revisions but the No. of companies that consistently get it wrong suggests there must be a better way.
Some consultants write a large part of them with no in depth understanding of the business they are writing for.
blakmax
Interesting to hear your thoughts of vacuum causing larger voids, we have used to remove excess resins & entrapped air rather than vapours, but I can follow the argument regarding humidity, something else to factor into the equation.
How would you guard against volatiles entrapment other than slow cure and super critical mixes ?
PS
I only scrape small portion of skin is this in keeping with the rugged down under
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Hi sorry I have been away, did the tail "Fall Off" or has the TRDS thrashed about following failure and "Severed" the tailboom. Have not had time to trawl all the way through the posts.
Cannot accept that a pilot with heavy feet could make it fall OFF, surely the design overload is there to cater for such an eventuality, over and over again.
If its about glue and sticky stuff not being sticky enough!!! then thats really shocking!!
God was smiling on the crew that day for sure.
DB
Cannot accept that a pilot with heavy feet could make it fall OFF, surely the design overload is there to cater for such an eventuality, over and over again.
If its about glue and sticky stuff not being sticky enough!!! then thats really shocking!!
God was smiling on the crew that day for sure.
DB
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DB
Subject to formal confirmation, I think we can be sure it failed and "fell off" as you say, mercifully just before take-off. As to whys and wherefores, it really would be worth your while trawling through the posts ans siphon out what blakmax in particular has to say about composites and their capacity to fail based on less then perfect production techniques. Supplemented by the observations of some people who've worked on this part of the aircraft, it all makes for very interesting reading.
22
Subject to formal confirmation, I think we can be sure it failed and "fell off" as you say, mercifully just before take-off. As to whys and wherefores, it really would be worth your while trawling through the posts ans siphon out what blakmax in particular has to say about composites and their capacity to fail based on less then perfect production techniques. Supplemented by the observations of some people who've worked on this part of the aircraft, it all makes for very interesting reading.
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clarification on vacuum
Hi 500e. Just to clarify about applying vacuum to remove air etc. That is a waise move and should be continued, but with some modification. It is important to remove trapped air.
The problem is that epoxies absorb humidity in the cured and especially the uncured state, and many small voids in composites and adhesive bonds are actually caused by release of that moisture as heat is applied. As the resin or adhesive becomes fluid, the bubble will expand because of the low pressure outside and the increasing pressure in the bubble. That forces the adhesive out. Very high vacuum and you end up with an aero-bar (a bubbly confectionery sold down under).
The trick is to make the voids smaller before the adhesive gels. Try this: Apply full vacuum during heat up so that any trapped air can be drawn out. Now once the adhesive has started to flow, reduce the vacuum to about 10 inches Hg (about 5 psi) for the rest of the cure cycle. There is enough pressure to hold the shape, but the voids reduce significantly because of the increase in pressure outside the joint.
Regards
blakmax
The problem is that epoxies absorb humidity in the cured and especially the uncured state, and many small voids in composites and adhesive bonds are actually caused by release of that moisture as heat is applied. As the resin or adhesive becomes fluid, the bubble will expand because of the low pressure outside and the increasing pressure in the bubble. That forces the adhesive out. Very high vacuum and you end up with an aero-bar (a bubbly confectionery sold down under).
The trick is to make the voids smaller before the adhesive gels. Try this: Apply full vacuum during heat up so that any trapped air can be drawn out. Now once the adhesive has started to flow, reduce the vacuum to about 10 inches Hg (about 5 psi) for the rest of the cure cycle. There is enough pressure to hold the shape, but the voids reduce significantly because of the increase in pressure outside the joint.
Regards
blakmax
Last edited by blakmax; 2nd Sep 2009 at 23:44. Reason: Oops. Tried to add images and that didn't work.
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Spinwing, Um..Lifting,
Thanks for the info, and the kind delivery.
You guys are seated up front while the turbines are running, I have to walk through the blast off the exhausts to ballast the aircraft before you get to settle back to cruise mode, and on specifically the Puma, it's ferkin murderous walking through the exhaust gas.
Assuming the turbines on the 139 and the puma are vaugely similar and the boom on the 139 is hovering (pun intentional) at around 80 Deg C on the helideck, backing upwards is going to put that slightly toasty exhaust gas right back back down on the boom about where it failed.
Now, it only takes 10 to 15 seconds to back up to 100' ato, you try putting yer face in the exhaust blast for 10 seconds and tell me it won't make a signifcant difference to the temperature of yer face (or the boom).
Say all you like about procedures for Cat ab, xy of anything at all, I write procedures for the stuff we do on the rigs, we guestimate at $41,500 / hr to run a rig offshore (inc all the support services) so, it's not small beer.
Just because it's written in a "procedure" does not make it right. these are procedures written by engineers unknown, not the holy grail. Any procedure is subject to review and input (not to be ignored or circumvented willy nilly)
By inference the recomendation from AW is to back the aircraft up from the helideck, putting hot exhaust gas over the boom (unless you can tell me it goes elsewhere ?) then transiton the heli into forward flight (I'm assuming there will be some difference in tailboom loads between backing and forward flight . . ?) with a now distinctly toasty composite, glued boom section.
The only comment from a pax pov on the GH crews is that they have been universally smooth, controlled and impressive.
If commenting on flight profiles is a faux pax on my part, well fly flight profiles that don't raise eyebrows elsewhere . . .
I fly gliders, in Scotland, in wave and have the utmost respect for rotary wing pilots.(some very senior rotary pilots also fly fixed wing and have taught me much over the years) None of this is meant as a "dig" at anyone, My arse is on the line as much as yours. I know that, even if some (pompous twats) dismiss it.
If Shell in the Hauge have not ceased 139 ops, subsiduaries elsewhere have.
Europe has _THE_ best composite manufacturing in the world. (notwithstanding input from elsewhere)
It is where F1 composites are manufactured, The best gliders in the world are manufactured, racing bicycle frames are manufactured, in short, Europeans are pretty good at sticking light things together.
Americans, are very good at building heavy and throwing horsepower at them afterwards. (which actually seems to be the way to go in many applications)
I go to play in glued structures and trust them implicitly, however, they are painted white (to keep the heat down) and don't carry kerosene burning turbines. They work very well from 20 Deg C to -30 Deg C.
I believe that the flown profiles are likely to significantly increase the temps on the booms.
From what I know of the properties of the adhesives, this is not a good thing.
I most certainly _AM NOT_ having a "go" at the guys who take me to work, who I believe to be doing a very good job with the equipment they have.
(now if "someone" would look in the direction the bus was going, I'd be even happier . . . .specifically on T.O.) Those rig legs are pretty solid.
Thanks for the info, and the kind delivery.
You guys are seated up front while the turbines are running, I have to walk through the blast off the exhausts to ballast the aircraft before you get to settle back to cruise mode, and on specifically the Puma, it's ferkin murderous walking through the exhaust gas.
Assuming the turbines on the 139 and the puma are vaugely similar and the boom on the 139 is hovering (pun intentional) at around 80 Deg C on the helideck, backing upwards is going to put that slightly toasty exhaust gas right back back down on the boom about where it failed.
Now, it only takes 10 to 15 seconds to back up to 100' ato, you try putting yer face in the exhaust blast for 10 seconds and tell me it won't make a signifcant difference to the temperature of yer face (or the boom).
Say all you like about procedures for Cat ab, xy of anything at all, I write procedures for the stuff we do on the rigs, we guestimate at $41,500 / hr to run a rig offshore (inc all the support services) so, it's not small beer.
Just because it's written in a "procedure" does not make it right. these are procedures written by engineers unknown, not the holy grail. Any procedure is subject to review and input (not to be ignored or circumvented willy nilly)
By inference the recomendation from AW is to back the aircraft up from the helideck, putting hot exhaust gas over the boom (unless you can tell me it goes elsewhere ?) then transiton the heli into forward flight (I'm assuming there will be some difference in tailboom loads between backing and forward flight . . ?) with a now distinctly toasty composite, glued boom section.
The only comment from a pax pov on the GH crews is that they have been universally smooth, controlled and impressive.
If commenting on flight profiles is a faux pax on my part, well fly flight profiles that don't raise eyebrows elsewhere . . .
I fly gliders, in Scotland, in wave and have the utmost respect for rotary wing pilots.(some very senior rotary pilots also fly fixed wing and have taught me much over the years) None of this is meant as a "dig" at anyone, My arse is on the line as much as yours. I know that, even if some (pompous twats) dismiss it.
If Shell in the Hauge have not ceased 139 ops, subsiduaries elsewhere have.
Europe has _THE_ best composite manufacturing in the world. (notwithstanding input from elsewhere)
It is where F1 composites are manufactured, The best gliders in the world are manufactured, racing bicycle frames are manufactured, in short, Europeans are pretty good at sticking light things together.
Americans, are very good at building heavy and throwing horsepower at them afterwards. (which actually seems to be the way to go in many applications)
I go to play in glued structures and trust them implicitly, however, they are painted white (to keep the heat down) and don't carry kerosene burning turbines. They work very well from 20 Deg C to -30 Deg C.
I believe that the flown profiles are likely to significantly increase the temps on the booms.
From what I know of the properties of the adhesives, this is not a good thing.
I most certainly _AM NOT_ having a "go" at the guys who take me to work, who I believe to be doing a very good job with the equipment they have.
(now if "someone" would look in the direction the bus was going, I'd be even happier . . . .specifically on T.O.) Those rig legs are pretty solid.
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blakmax, with your experience it would be interesting to hear your thoughts on where we are going with composites, as in the Boeing 787. Perhaps you could start a thread in Tech Log, or where ever the Mods might suggest.
airwave45,
Now you've really got me thinking..... I have never heard of any offshore helis using a back-up take off profile on jack up rigs unless it is away from the deck into clear air over the sea. The 139 does have a very tail down attitude of around 7-10 degs, which would be exaggerated from a pax in the back point of view, and with the normal "towering take off" profile from offshore installations, could feel like a back up profile is being used? If they truly are using the profile you suggest, I would be F*****G gobsmacked
As for the tailboom theories/bonding issues... I will leave that to some extremely experienced pruners on this thread, but my two cents worth is that its been operating in the gulf of Mexico for many, many years without any issues with the tail or exhaust gas problems, and lets remember, its not made of chocolate!!
I think its Mr Plum in the repair room with a glue stick
Now you've really got me thinking..... I have never heard of any offshore helis using a back-up take off profile on jack up rigs unless it is away from the deck into clear air over the sea. The 139 does have a very tail down attitude of around 7-10 degs, which would be exaggerated from a pax in the back point of view, and with the normal "towering take off" profile from offshore installations, could feel like a back up profile is being used? If they truly are using the profile you suggest, I would be F*****G gobsmacked
As for the tailboom theories/bonding issues... I will leave that to some extremely experienced pruners on this thread, but my two cents worth is that its been operating in the gulf of Mexico for many, many years without any issues with the tail or exhaust gas problems, and lets remember, its not made of chocolate!!
I think its Mr Plum in the repair room with a glue stick
Griffo,
I was surpsrised too, but on checking the RFM I see that there is indeed a back up procedure for elevated helidecks! I would have thought it was intended for hospital roof tops and the like - not Jack Up Rigs
By the way, I don't believe this procedure would have any adverse effect on the tailboom heating relative to the overall useage - there are too many variables and too brief an exposure. Heating from exhausts can be an issue in general though, and I know a previous type I flew had a modification to the tail rotor drive cover for this reason.
I was surpsrised too, but on checking the RFM I see that there is indeed a back up procedure for elevated helidecks! I would have thought it was intended for hospital roof tops and the like - not Jack Up Rigs
By the way, I don't believe this procedure would have any adverse effect on the tailboom heating relative to the overall useage - there are too many variables and too brief an exposure. Heating from exhausts can be an issue in general though, and I know a previous type I flew had a modification to the tail rotor drive cover for this reason.
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Elevated Heliupad Take-off Technique
CAT A (Group A) (Class 1) Elevated Heliport Techniques have traditionally ALWAYS employed a reverse flight profile from the helipad up to and between 80 and 200 feet dependant on the type or any obstacles that may be in front of you.
Offshore Helicopter Operations are conducted (generally) under the alleviations afforded by JAR-OPS 3.517 - Take-off and Landing with Exposure (ie. the inference being that should the engine fail during the "Exposed" period, a safe forced landing may not be assured).
This situation exists partly due to the vaguaries of the offshore environment, turbulence around helidecks and so forth, and partly because it is not really possible to determine the performance of the helicopter prior to arrival at the deck, due to the obstacle environment etc.
The "Exposure" period is also "Theoretical" because if it was not; the only time you would realise that you may or may not have exceeded the exposure period, is when it actually happens, and guess what, you are already exposed.
The implied risks associated with operating with an exposure period during take-off and landing are mitigated by the requirements of the approval, in that to be so approved you must operate the helicopter under an engine reliability programme, have a full HUMs kit and protocols fitted for trend monitoring, AND MOST SIGFNIFICANTLY operate the helicopter IAW the procedures acceptable to the authority.
These proicedures were first published under JAR-TGL 14 and follow in principle the older HAPs modelling studies for offshore operations. These procedures DO NOT incorporate a reverse flight take-off procedure. They are based on a vertical take-off to a TDP of approx 25 feet and then a rotation away from the deck using the momentum of the intitial vertical climb to hopefully clear the tail should an engine fail. There is no performance solution in play and safety is assured by the close monitoring of the 2 engines in play as indicated earlier to provide an assurance within defined acceptable probabilities that neither engine will fail .
I do not know what kind of approval the AW139 has for offshore, and although the Operator may be JAR-OPS, the Procedures they are required to operate must be acceptable to their responsible Authority which may differ from those currently applied in the UK-NS sector.
From a performance point of view, ignoring the turbulence environment for a moment, a helicopter conducting the CAT A approved Elevated Helipad Profile, at the correct mass for WAT, has the capability in the event of OEI to either, Re-land safely back on the helipad, or, continue the take-off safely, meeting all required safety margins, depending on the point in the profile at which the OEI occurred.
For a helicopter operating to TGL-14 and the HAPs model, this absolute level of safety in the event of OEI is not provided, but may be there depending on the ambient operating conditions and obstacle environment.
THEREFORE - if some offshore operators are electing to (or required to) use a CAT A technique offshore, from a performance point of view, provided the ambient conditions and obstacle environment is suitable, the helicopter is being operated to a greater level of safety than one using the JAR-OPS 3.517 Class 2 With Exposure alleviations.
Hope this helps.
Offshore Helicopter Operations are conducted (generally) under the alleviations afforded by JAR-OPS 3.517 - Take-off and Landing with Exposure (ie. the inference being that should the engine fail during the "Exposed" period, a safe forced landing may not be assured).
This situation exists partly due to the vaguaries of the offshore environment, turbulence around helidecks and so forth, and partly because it is not really possible to determine the performance of the helicopter prior to arrival at the deck, due to the obstacle environment etc.
The "Exposure" period is also "Theoretical" because if it was not; the only time you would realise that you may or may not have exceeded the exposure period, is when it actually happens, and guess what, you are already exposed.
The implied risks associated with operating with an exposure period during take-off and landing are mitigated by the requirements of the approval, in that to be so approved you must operate the helicopter under an engine reliability programme, have a full HUMs kit and protocols fitted for trend monitoring, AND MOST SIGFNIFICANTLY operate the helicopter IAW the procedures acceptable to the authority.
These proicedures were first published under JAR-TGL 14 and follow in principle the older HAPs modelling studies for offshore operations. These procedures DO NOT incorporate a reverse flight take-off procedure. They are based on a vertical take-off to a TDP of approx 25 feet and then a rotation away from the deck using the momentum of the intitial vertical climb to hopefully clear the tail should an engine fail. There is no performance solution in play and safety is assured by the close monitoring of the 2 engines in play as indicated earlier to provide an assurance within defined acceptable probabilities that neither engine will fail .
I do not know what kind of approval the AW139 has for offshore, and although the Operator may be JAR-OPS, the Procedures they are required to operate must be acceptable to their responsible Authority which may differ from those currently applied in the UK-NS sector.
From a performance point of view, ignoring the turbulence environment for a moment, a helicopter conducting the CAT A approved Elevated Helipad Profile, at the correct mass for WAT, has the capability in the event of OEI to either, Re-land safely back on the helipad, or, continue the take-off safely, meeting all required safety margins, depending on the point in the profile at which the OEI occurred.
For a helicopter operating to TGL-14 and the HAPs model, this absolute level of safety in the event of OEI is not provided, but may be there depending on the ambient operating conditions and obstacle environment.
THEREFORE - if some offshore operators are electing to (or required to) use a CAT A technique offshore, from a performance point of view, provided the ambient conditions and obstacle environment is suitable, the helicopter is being operated to a greater level of safety than one using the JAR-OPS 3.517 Class 2 With Exposure alleviations.
Hope this helps.
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Mmmmm ....
Ok ... Heli Ops (Offshore) in the UAE at the moment do NOT have to operate to PC1 requirements.
I do not know if they have to in the State of Qatar .... I very much doubt it.
As 'Griffo' and I both know the decks on most 'jack ups' used in the Arabian Gulf are generally a bit on the small size and therefore I really doubt if a "back up' type take off procedure is used ... it'd be a short route to either disaster or un-employment to do so! (and I might add I recently lost a collegue to what has been assumed to be a 'backing up accident' so I'm a bit sensitised to them).
As "DB" indicated ... the 'normal' take-off is 'usually' to a hover then to lift to 25-40' above the deck if nothing untoward has occurred then 'rotation' happens and using the a/c momentum to clear the deck if it were to go wrong from that point.
NOW can we keep this thread on track with the regard the 139 bonding issues ... especially as I see there is another thread has been started to take care of the rig takeoff 'red herring' ...
Cheers
Ok ... Heli Ops (Offshore) in the UAE at the moment do NOT have to operate to PC1 requirements.
I do not know if they have to in the State of Qatar .... I very much doubt it.
As 'Griffo' and I both know the decks on most 'jack ups' used in the Arabian Gulf are generally a bit on the small size and therefore I really doubt if a "back up' type take off procedure is used ... it'd be a short route to either disaster or un-employment to do so! (and I might add I recently lost a collegue to what has been assumed to be a 'backing up accident' so I'm a bit sensitised to them).
As "DB" indicated ... the 'normal' take-off is 'usually' to a hover then to lift to 25-40' above the deck if nothing untoward has occurred then 'rotation' happens and using the a/c momentum to clear the deck if it were to go wrong from that point.
NOW can we keep this thread on track with the regard the 139 bonding issues ... especially as I see there is another thread has been started to take care of the rig takeoff 'red herring' ...
Cheers
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OK..Do I keep posting here or what?
Spinwing
I am not too sure if you want to continue my discussions on adhesive bonding issues here, or should I also start a new thread eleswhere? I did start a new thread on 787 composite issues in response to Brian Abraham's request because that is really far from the AW139 issue.
I'll take guidance here. Do I start a new thread to talk about generic bonding issues, do I continue posting here or do I simply make love elsewhere (F**&&* off)? The subject is of relevance to the current thread but the subject may be more happily located elsewhere if requested.
Regards
Blakmax
I am not too sure if you want to continue my discussions on adhesive bonding issues here, or should I also start a new thread eleswhere? I did start a new thread on 787 composite issues in response to Brian Abraham's request because that is really far from the AW139 issue.
I'll take guidance here. Do I start a new thread to talk about generic bonding issues, do I continue posting here or do I simply make love elsewhere (F**&&* off)? The subject is of relevance to the current thread but the subject may be more happily located elsewhere if requested.
Regards
Blakmax
Chief Bottle Washer
blakmax,
I think that most of us agree that your dissertations in this thread are both informative, and very relevant to the AW139 topic under discussion. Unless you specifically want to create a new thread on Rotorheads, I would rather see your posts staying here
I think that most of us agree that your dissertations in this thread are both informative, and very relevant to the AW139 topic under discussion. Unless you specifically want to create a new thread on Rotorheads, I would rather see your posts staying here
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Mmm ...
blakmax ....
I consider your posts to be extremely relevant to this thread ... and also very educational.
Please, please do continue ..... I was more concerned with the possibility of a "thread hijack' with regard rig take offs ... which I really thought bore no relation to the 139 de-bonding issues.
Your input IS very valuable!
Cheers
blakmax ....
I consider your posts to be extremely relevant to this thread ... and also very educational.
Please, please do continue ..... I was more concerned with the possibility of a "thread hijack' with regard rig take offs ... which I really thought bore no relation to the 139 de-bonding issues.
Your input IS very valuable!
Cheers
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don't shoot the messenger
Guys (and girls) and for the down under crowd, Blokes and Shielas (strewth, Bruce that is laying it on a bit thick!)
The rig focussed group really do have a point. If the thermal shock loading is high, the moisture evolved will produce sufficient cell pressure to force the skin off weakly bonded sandwich structure. Recognise that this is the initiating mechanism, not the root cause of the problem, which still remains a processing issue resulting in weak core to adhesive bonds which fail when subjected to excessive cell pressure.
It is still a bonding issue, Agusta.
Regards
Blakmax
The rig focussed group really do have a point. If the thermal shock loading is high, the moisture evolved will produce sufficient cell pressure to force the skin off weakly bonded sandwich structure. Recognise that this is the initiating mechanism, not the root cause of the problem, which still remains a processing issue resulting in weak core to adhesive bonds which fail when subjected to excessive cell pressure.
It is still a bonding issue, Agusta.
Regards
Blakmax
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Unless a report has been issued or you have examined the damage yourself are the highlighted words not a bit presumptuous?:
Or are you in fact the messenger for someone with an ax to grind?
Recognise that this is the initiating mechanism, not the root cause of the problem, which still remains a processing issue resulting in weak core to adhesive bonds which fail when subjected to excessive cell pressure.
It is still a bonding issue, Agusta.
It is still a bonding issue, Agusta.