If there was a change to the assumptions or known modality of failure that would otherwise alter the original assessment to certify, one would think that a reassessment would be in order. Do we know if such a reassessment was conducted after the Broome incident?
Better yet.....why not make it an internal filter....build it into the case...cover it with a blank gasketed cover then even if the filter bowl separates for any reason the oil is trapped "inside" the Gear Box.
Sikorsky uses internal oil passages rather than using external piping to get the oil around the case as it is.
The key is to keep the oil "inside" the gear box as much as possible and limit the sources of "external" leaks as much as possible.
"...build it into the case...cover it with a blank gasketed cover then even if the filter bowl separates for any reason the oil is trapped "inside" the Gear Box."
You still have a cover and a gasket with attaching hardware to hold the cover on, that mechanics need to remove and install during inspections.
Mounting the filter in the external system would address these human factors.
Have you ever seen a gasket blow out on a Huey transmission internal oil filter? All the oil goes away....
I have posted that the Cougar accident had great similarity to the Shuttle Challenger and that the Fineman Appendix F of that report discusses how this can happen.
Now it appears Columbia suffered the same fate. Lessons never learned.
Linked article of interest. Especially the crew saying it looks bad and managers saying it did not look too bad to them.
The relevance is the mind set of decision making which does not extrapolate the potential results of an event and mitigate the chance of the worst case scenarios.
I have been looking for my copy of the HARP Report (Helicopter Airworthiness Review Panel) produced by the UK CAA in the 80s following too many helicopter accidents that had technical related issues - can't find it so this is from memory.
The report essentially said that many aspects of helicopter design equated to the Dakota era of fixed wing design and that transmissions that included high speed sections within the main casing like the S61 - which at that time dominated the offshore world - were definately out of order. The report implored manufacturers to find a better way with less criticality. I believe the 30 minute run-dry time was meant to indicate that the design indeed had less critical failure modes. I don't believe it was ever envisaged that we, the flight crew, would interpret that to mean that it gave us more 'get-you-home' time. It is easy to see though that when you are up against it the pressure is on to make it those last few miles to the beach.
I recommend the HARP report (maybe someone can post a link if it exists on-line) because I think that as a retrospective it would make fascinating reading in the context of recent developments.
The "no oil" capabilities of the 60 was in the Army -10 in 2007. Dont know what it says currently. Remembering back to 2007 I recall that anytime a transmission oil pressure low situation was introduced in the 60 simulator, the following would happen. Oil px low light, rapidly followed by: TX Oil hot, multiple chip lights then within approx 2 minutes horrible noise and general breakdown. I dont know if the simulator software is based on manufacturers (Sikorsky) data from tests, or if it is programmed according to the Armys own experiences with gearbox problems. Anyhow I think the message the Army is giving its aviators both in emergency drills and simulator use is: Anytime you have main transmission issues....land without delay!
It would be very interesting to know what the Navy an AF says for the same gearbox related malfunctions in the HH-60. The Army in most cases operate over Terra Firma vs Navy blue water ops (offshore) considerations.
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:
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
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.
Last edited by outhouse : 29th March 2009 at 15:55.
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.
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.
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?
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
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.
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.
Last edited by nl_backseater : 31st March 2009 at 17:53.
Reason: add clarification
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.
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