Sikorsky S-92: From Design to Operations
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Geoffers,
The 1984 CAP 491, HARP Report to which you refer doesn't seem to be available electronically; only CAP 641, Report of the Review of Helicopter Offshore Safety and Survival, published in 1995, which refers to it:
Report of the Review of Helicopter Offshore Safety and Survival,
or the AW presentation New Technologies in Rotorcraft Mechanical & Rotor Systems:
New Technologies in Rotorcraft Mechanical Rotor Systems
both of which also make for interesting reading with regard to ditching survivability and improved engineering concepts.
CAP 641 was updated in 2005 by:
Helicopter Ditching and Crashworthiness Research
The UK HSE also has some interesting on changing helicopter accident rates in the UK sector:
Helicopter safety
Sorry, that hasn't answered your question and is a bit of thread creep, but all are interesting documents in view of recent tragedies in the offshore helicopter world
The 1984 CAP 491, HARP Report to which you refer doesn't seem to be available electronically; only CAP 641, Report of the Review of Helicopter Offshore Safety and Survival, published in 1995, which refers to it:
Report of the Review of Helicopter Offshore Safety and Survival,
or the AW presentation New Technologies in Rotorcraft Mechanical & Rotor Systems:
New Technologies in Rotorcraft Mechanical Rotor Systems
both of which also make for interesting reading with regard to ditching survivability and improved engineering concepts.
CAP 641 was updated in 2005 by:
Helicopter Ditching and Crashworthiness Research
The UK HSE also has some interesting on changing helicopter accident rates in the UK sector:
Helicopter safety
Sorry, that hasn't answered your question and is a bit of thread creep, but all are interesting documents in view of recent tragedies in the offshore helicopter world
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As this will I think be my last post on this subject until an opportunity to view the full TSB report and the findings and recommendation is forthcoming I would now rather just view the posts presented.
However having today spoken to a person closely involved in a certification process conducted by a European manufacture to meet the JAA/EASA requirements, maybe it’s time to look at the agreements that exist for transfer of Type Approvals, acceptance and interpretation of requirements used to certify.
It would seem a level playing field may be missing. Also maybe some authorities should revisit the original test data to determine its validity.
Regarding the comment posted below, JAA/EASA to my knowledge accepted a true test, maybe the FAA should check again for compliance.
It is the FAA and JAA/EASA that need to be looking at their belly buttons.
Back when valid data and info available for further comment.
O.
However having today spoken to a person closely involved in a certification process conducted by a European manufacture to meet the JAA/EASA requirements, maybe it’s time to look at the agreements that exist for transfer of Type Approvals, acceptance and interpretation of requirements used to certify.
It would seem a level playing field may be missing. Also maybe some authorities should revisit the original test data to determine its validity.
Regarding the comment posted below, JAA/EASA to my knowledge accepted a true test, maybe the FAA should check again for compliance.
It is the FAA and JAA/EASA that need to be looking at their belly buttons.
Back when valid data and info available for further comment.
O.
Last edited by outhouse; 29th Mar 2009 at 14:55.
Outhouse,
In the past there has been efforts by Non-French entities to obtain Test Standards, Test Plans, Test Data and the like from the French authorities and nothing was released. The issue I am familiar with regards the Puma Certification process.
EC and the French Government have a very cozy relationship thus it is a one way street in both directions and not quite as simple as your post would suggest I fear.
I like you would rather it be a fully cooperative environment rather than it appears to be currently.
In the past there has been efforts by Non-French entities to obtain Test Standards, Test Plans, Test Data and the like from the French authorities and nothing was released. The issue I am familiar with regards the Puma Certification process.
EC and the French Government have a very cozy relationship thus it is a one way street in both directions and not quite as simple as your post would suggest I fear.
I like you would rather it be a fully cooperative environment rather than it appears to be currently.
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This thread,
seems to be a long, long process of re-iteration.
For sure nothing runs without oil,
countersunk teflon inserts or some other magic.
From what we see as casual observers, not one,
I mean not one person has come up with an idea,
that these super hi-tech latest generation gearboxes will run
‘without’, a necessary lubricant, fat, green bananas or good ol’ oil.
Maybe, just maybe for alla you old time dudes,
it would be worth showing humility and leadership;
Especially to the hi-tech and impressionable kids
who graduate from a very low time ATPL,
to the esteemed position of number two
on the flight deck of these super hi-tech turnouts.
Remember they have not the hindsight of feel or fable,
so just in case they have to make a decision
based on fact, instead of rhetorical hyperbole,
pilot room humbug or beer hall idiocy,
That they be instructed in three auld rules
of absolute old time value.
One.
If you ever are in doubt land.
Two.
If the oil pressure fails, land.
Three.
Never, but never fly too high,
lest, a simple failure,
becomes a total catastrophe.
And, in case you are totally dumb;
and still in doubt, see one an’ all above.
And;
Read, learn, understand your POH.
seems to be a long, long process of re-iteration.
For sure nothing runs without oil,
countersunk teflon inserts or some other magic.
From what we see as casual observers, not one,
I mean not one person has come up with an idea,
that these super hi-tech latest generation gearboxes will run
‘without’, a necessary lubricant, fat, green bananas or good ol’ oil.
Maybe, just maybe for alla you old time dudes,
it would be worth showing humility and leadership;
Especially to the hi-tech and impressionable kids
who graduate from a very low time ATPL,
to the esteemed position of number two
on the flight deck of these super hi-tech turnouts.
Remember they have not the hindsight of feel or fable,
so just in case they have to make a decision
based on fact, instead of rhetorical hyperbole,
pilot room humbug or beer hall idiocy,
That they be instructed in three auld rules
of absolute old time value.
One.
If you ever are in doubt land.
Two.
If the oil pressure fails, land.
Three.
Never, but never fly too high,
lest, a simple failure,
becomes a total catastrophe.
And, in case you are totally dumb;
and still in doubt, see one an’ all above.
And;
Read, learn, understand your POH.
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S92 Filter Bowl Assembly.
Just wondering but is the arrangement of the S92 MGB filter housing the same or relatively close to that of the Blackhawk/Seahawk? upon which the S92 drive system is based.
If so have there ever been any issues with MGB oil leaks on that line of helo's from the same type of failure as has now occurred twice with the S92?
If so have there ever been any issues with MGB oil leaks on that line of helo's from the same type of failure as has now occurred twice with the S92?
UH-60 Main Gearbox Filter Installation
On Blackhawk, the filter is mounted up inside the main sump. Access is from the bottom of the transmission.
Thanks,
John Dixson
Thanks,
John Dixson
Whoa hold on there John!
Someone told us that would not work.....that all we had to do was look at Bell 205/UH-1 Trannys and we would know that!
Now....as I know you speak with certainty of knowledge.....why did the 92 go with the external filter with only three studs to secure the thing?
If it had been an MBB thing it would have had a dozen or so probably and they would certainly have been over engineered to beat the band.
If this exterior thing would have had five or seven studs....would we have had the failures we have seen?
Someone told us that would not work.....that all we had to do was look at Bell 205/UH-1 Trannys and we would know that!
Now....as I know you speak with certainty of knowledge.....why did the 92 go with the external filter with only three studs to secure the thing?
If it had been an MBB thing it would have had a dozen or so probably and they would certainly have been over engineered to beat the band.
If this exterior thing would have had five or seven studs....would we have had the failures we have seen?
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Engineers designing any system have a choice, minimum to meet standards, add a safety factor, over engineer. Seems three studs is a minimum to meet standards, four studs add a safety factor and 5 well, over engineering and annoying when changing the component.
O
O
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SASless
3 points, 120° apart is the most optimum, and also minimum for stable mount of anything... the problem is - it gives no redundancy. Depending on what it does - if one fail - the whole thing no longer serve it purpose.. or the other two will surely fail with time (rather short).
For example, a 4 legged table is problematic if one leg is shorter, there is no such problem in 3 legged table, but a two legged can't exist.
I don't know what kind of forces that filter bowl have cope with in S-92, except the vibrations is there a pressure on it?
In design world, it's usually making things as light, cheap and easy to make and use as possible, while still performing its task with some specific safety factor. The material used have usually no significance whatsoever - its strengths and shortcomings are known, so the parts are engineered to use all the pros, and limit the cons. If the design criteria are the same - in the end it doesn't matter if it is titanium, steel or spider web, it will do what it should, and will brake at the same point. Though the costs, size and weight will be different.
If the whole thing broke because of that one stud, the design criteria were wrong. Maybe 6 would safe the day... though gave ground crew hell, requiring twice the time to mount and dismount.
And BTW, my take on designing flaws is this: ANY part breakage is because the design was wrong - either the design criteria was wrongly assumed, or manufacturing process overly trusted, or some types of misuse not foreseen. Call it 'engineer paranoia', but it's true if you think about it
Foreseen everything - that's what is teached in programing, and I'm trying to use in engineering... though cost savings are usually what cuts engineers wings.
3 points, 120° apart is the most optimum, and also minimum for stable mount of anything... the problem is - it gives no redundancy. Depending on what it does - if one fail - the whole thing no longer serve it purpose.. or the other two will surely fail with time (rather short).
For example, a 4 legged table is problematic if one leg is shorter, there is no such problem in 3 legged table, but a two legged can't exist.
I don't know what kind of forces that filter bowl have cope with in S-92, except the vibrations is there a pressure on it?
In design world, it's usually making things as light, cheap and easy to make and use as possible, while still performing its task with some specific safety factor. The material used have usually no significance whatsoever - its strengths and shortcomings are known, so the parts are engineered to use all the pros, and limit the cons. If the design criteria are the same - in the end it doesn't matter if it is titanium, steel or spider web, it will do what it should, and will brake at the same point. Though the costs, size and weight will be different.
If the whole thing broke because of that one stud, the design criteria were wrong. Maybe 6 would safe the day... though gave ground crew hell, requiring twice the time to mount and dismount.
And BTW, my take on designing flaws is this: ANY part breakage is because the design was wrong - either the design criteria was wrongly assumed, or manufacturing process overly trusted, or some types of misuse not foreseen. Call it 'engineer paranoia', but it's true if you think about it
Foreseen everything - that's what is teached in programing, and I'm trying to use in engineering... though cost savings are usually what cuts engineers wings.
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S92 Filter Bowl Assembly.
My thanks to JD for his quick response about the lack of commonality of the Blackhawk filter mount to the S92. It seems my first post has elicited some interesting debate on the MGB filter design of the S92 and I don't think it could be summed up any better than Lt.Fubar's post. Kudo's for bringing an analogy to the discussion that everyone can understand. Including mere PAX like me.
Having said that we have what we have with the existing design and certainly the fix proposed raises the same concerns that became evident with the titanium studs. Will the steel studs fair any better in the long run?
So, another question or maybe two or three.
What is the inspection or change interval for the filter?
Is it being handled by maintenance staff more often than recommended because of the issues with the pumps and the accelerated inspection/change schedule? It seems to make some sense to me that perhaps a cursory inspection of the filter might be called for to check for trapped particulate that might be shed form the pump splines.
Or, have the pump issues been worked out with the latest rev pumps so that maintenance is again being performed at the original maintenance intervals?
The reason I ask is because it was postulated in one post that the constant loosening and re-torquing may have played a part in the studs failing. Certainly if the filter housing is being removed more frequently it would only add to these concerns.
Including mere PAX like me.Having said that we have what we have with the existing design and certainly the fix proposed raises the same concerns that became evident with the titanium studs. Will the steel studs fair any better in the long run?
So, another question or maybe two or three.
What is the inspection or change interval for the filter?
Is it being handled by maintenance staff more often than recommended because of the issues with the pumps and the accelerated inspection/change schedule? It seems to make some sense to me that perhaps a cursory inspection of the filter might be called for to check for trapped particulate that might be shed form the pump splines.
Or, have the pump issues been worked out with the latest rev pumps so that maintenance is again being performed at the original maintenance intervals?
The reason I ask is because it was postulated in one post that the constant loosening and re-torquing may have played a part in the studs failing. Certainly if the filter housing is being removed more frequently it would only add to these concerns.
Last edited by nl_backseater; 31st Mar 2009 at 16:53. Reason: add clarification
S-92 Filter Bowl Assembly
NL, I just cannot recall how the decisioning went as to the filter install location on the S-92. I can guess that one factor was ease of access. On the Hawk, all one does to get at the filter is remove the troop seats and very simple cargo compartment roofing. And by the way, when the filter is pulled, some rags and a container are necessary, as there is the possibility( probability in my experience ) of a bit of oil spillage. In the S-92 the interior roofing is much different. More complicated, bigger parts, not inexpensive and items that you don't want to get oil-stained. Just a guess on my part.
John Dixson
John Dixson
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Thanks, again John. That basically confirms my visualization of your description from the earlier post on the Blackhawk MGB filter location. I can see how this setup would not be desirable for the S92 because of the potential for soilage of the passenger cabin. On the other hand I can also see that this setup turns the filter replacement into an inside job sheltered from the elements and that might be desirable in a field locale. Messy perhaps but away from the rain, snow, or sand. Makes a lot of sense for a military helo.
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John D, appreciate your knowledge sharing of the Blackhawk design, hopefully valuable design lessons can be learned for the S-92b when it invariably comes out.
Can you please confirm how many mounting studs are on the UH-60, 3 as in the S-92? Also, can you confirm if the UH-60 does indeed have 30-minute dry-run capability? What is the vibration level in a UH-60 like compared to a S-92a?
I'm assuming that there is a sump drain plug but with a bottom-mounted filter housing there will be a certain amount of residual oil retained during changeout/inspection. On the plus side the PAX would hopefully be able to visually confirm an oil leak and inform the pilot to commence the RFM procedure.
FYI Cougar are officially test-flying the S92 over St. John's and the sole survivor from flight 491 has been released from hospital to continue his recovery at home, but will probably not share his account of events for a few more weeks yet.
Can you please confirm how many mounting studs are on the UH-60, 3 as in the S-92? Also, can you confirm if the UH-60 does indeed have 30-minute dry-run capability? What is the vibration level in a UH-60 like compared to a S-92a?
I'm assuming that there is a sump drain plug but with a bottom-mounted filter housing there will be a certain amount of residual oil retained during changeout/inspection. On the plus side the PAX would hopefully be able to visually confirm an oil leak and inform the pilot to commence the RFM procedure.
FYI Cougar are officially test-flying the S92 over St. John's and the sole survivor from flight 491 has been released from hospital to continue his recovery at home, but will probably not share his account of events for a few more weeks yet.
UH-60 Run Dry
Maxwelg2, to answer your questions in order:
1. Re H-60 filter mounting studs: I had posted earlier that in the Hawk, the filter is mounted internally, in the Main Box sump. I cannot tell you how many fasteners attach it inside as I don't know.
2. The UH-60 Main Box was tested and qualified to run at 30 minutes under cruise power conditions. The flight manual reflects that capability. ( Same goes for tail and intermediate boxes ).
3. As to vibration levels, I assume that you are addressing the vibration levels present at the S-92 filter attachment point, which cannot be deduced from cockpit vibration levels. On that subject, I am simply not aware of what those localized levels are. As to cockpit N/rev comparisons between the H-60 and S-92, I'd say that at design gross weight and 145 KIAS, at say 0-2000 ft altitude, and with a properly maintained vibration attenuation system in each machine, the UH-60 is roughly the same as an S-92 with the three force generator attenuation system. The S-92 with the six force generator attenuation system is markedly smoother.
Thanks,
John Dixson
1. Re H-60 filter mounting studs: I had posted earlier that in the Hawk, the filter is mounted internally, in the Main Box sump. I cannot tell you how many fasteners attach it inside as I don't know.
2. The UH-60 Main Box was tested and qualified to run at 30 minutes under cruise power conditions. The flight manual reflects that capability. ( Same goes for tail and intermediate boxes ).
3. As to vibration levels, I assume that you are addressing the vibration levels present at the S-92 filter attachment point, which cannot be deduced from cockpit vibration levels. On that subject, I am simply not aware of what those localized levels are. As to cockpit N/rev comparisons between the H-60 and S-92, I'd say that at design gross weight and 145 KIAS, at say 0-2000 ft altitude, and with a properly maintained vibration attenuation system in each machine, the UH-60 is roughly the same as an S-92 with the three force generator attenuation system. The S-92 with the six force generator attenuation system is markedly smoother.
Thanks,
John Dixson
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Titanium fasteners?
Does anyone have info on the normal maintenance cycle of the S92 MGB filter assembly? And particularly if it has been inadvertently accelerated because of increased attention given to other areas of the MGB. Just curious here about the frequency that the fasteners are removed and reinstalled.
I've been informed by an S92 pilot that there are other titanium studs/bolts that keep key components attached to the main gearbox, most notably the MGB oil pumps themselves. I do know that these pumps have an accelerated maintenance cycle mandated by an airworthiness directive so the attachment fixtures are obviously being loosened/torqued more often.
I wonder if anyone is concerned with these bolts and the possibility of fretting/galling of the titanium fasteners and possible failure? I don't know the number of bolts involved so it may not have as much potential.
I've been informed by an S92 pilot that there are other titanium studs/bolts that keep key components attached to the main gearbox, most notably the MGB oil pumps themselves. I do know that these pumps have an accelerated maintenance cycle mandated by an airworthiness directive so the attachment fixtures are obviously being loosened/torqued more often.
I wonder if anyone is concerned with these bolts and the possibility of fretting/galling of the titanium fasteners and possible failure? I don't know the number of bolts involved so it may not have as much potential.
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To Fixed Wing Jockey:
I know that you posed this question to maxwelg2 but since we're in the same boat literally and travelling to/from the offshore by supply vessel, I thought I might add my thoughts if you don't mind. I do know that max is offshore at the moment but I'm sure he'll respond when he can get the time.
For me getting back in the 92 will be all about mitigating the risks associated with ditching because the chances of that happening now seem to have increased. The seas in the North Atlantic are rough so I think that a bare minimum would be to outfit all of Cougar's S-92's with the more robust float package. I know that there's a payload penalty but passengers will insist that safety comes first.
Second I think that flights should have a maximum ceiling of 4-5 thousand feet, as suggested by pilots on this board We don't need to waste precious minutes getting down to the water by flying at 9-10 thousand feet if a problem occurs. Third, maybe we need to have some reasonable sea state limitations to ensure that the passengers and crew of a ditched helicopter have a reasonable expectation of survivable.
I know that there are other more terrifying ways to come back to earth in a chopper such as what happened to the Bond Super Puma the other day but I try not to think of those scenarios.
I know that you posed this question to maxwelg2 but since we're in the same boat literally and travelling to/from the offshore by supply vessel, I thought I might add my thoughts if you don't mind. I do know that max is offshore at the moment but I'm sure he'll respond when he can get the time.
For me getting back in the 92 will be all about mitigating the risks associated with ditching because the chances of that happening now seem to have increased. The seas in the North Atlantic are rough so I think that a bare minimum would be to outfit all of Cougar's S-92's with the more robust float package. I know that there's a payload penalty but passengers will insist that safety comes first.
Second I think that flights should have a maximum ceiling of 4-5 thousand feet, as suggested by pilots on this board We don't need to waste precious minutes getting down to the water by flying at 9-10 thousand feet if a problem occurs. Third, maybe we need to have some reasonable sea state limitations to ensure that the passengers and crew of a ditched helicopter have a reasonable expectation of survivable.
I know that there are other more terrifying ways to come back to earth in a chopper such as what happened to the Bond Super Puma the other day but I try not to think of those scenarios.
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nl backseater
I think your questions are exactly on the right track and am willing to bet a Canadian dollar the NSTB findings will reflect the broken stud was related to the amount of times it was taken off and replaced , and how the torque sequence was applied.
Any gasket mounted fixture (oil filter) has an inheritant flexability at the mounting base because of the (rubber) seal.
More of a problem with a 3 point fastener system. For example if the first fastener was run to it's maximum depth , even just finger tight , and the next 2 were properly torqued to spec it is possible to exert 10 times the stress on the original fastener because of the inheritant rocking movement and leverage of a 3 point flange.
Systematic torquing each fastener in equal increments would avoid this , but is it always done that way? I would guess not sometimes.
I think your questions are exactly on the right track and am willing to bet a Canadian dollar the NSTB findings will reflect the broken stud was related to the amount of times it was taken off and replaced , and how the torque sequence was applied.
Any gasket mounted fixture (oil filter) has an inheritant flexability at the mounting base because of the (rubber) seal.
More of a problem with a 3 point fastener system. For example if the first fastener was run to it's maximum depth , even just finger tight , and the next 2 were properly torqued to spec it is possible to exert 10 times the stress on the original fastener because of the inheritant rocking movement and leverage of a 3 point flange.
Systematic torquing each fastener in equal increments would avoid this , but is it always done that way? I would guess not sometimes.