Sikorsky S-92: From Design to Operations
Horror,
AVC are generally required for high speed cruise to reduce vibration levels. They are generally poor for tranistory activities due to lag times. On takeoff there should be little vibratory forces coming down from the rotor between takeoff and climb out that would require an AVC. Also AVC's only handle one frequency (n/rev where n is the number of blades). These kind of aborts are generally 1/rev where something let go in the main or tail rotor.
Now if the AVC went ape-s**t which they can do would be an issue, but I do not see why that would happen as going to forward speed. It should show up in hover.
The Sultan
AVC are generally required for high speed cruise to reduce vibration levels. They are generally poor for tranistory activities due to lag times. On takeoff there should be little vibratory forces coming down from the rotor between takeoff and climb out that would require an AVC. Also AVC's only handle one frequency (n/rev where n is the number of blades). These kind of aborts are generally 1/rev where something let go in the main or tail rotor.
Now if the AVC went ape-s**t which they can do would be an issue, but I do not see why that would happen as going to forward speed. It should show up in hover.
The Sultan
Last edited by The Sultan; 22nd Dec 2010 at 03:13.
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Moving forward six years plus...
It's time to resurrect this blog. It looks like the S92 still has issues that haven't been resolved. Many seem to think that the EC225 should be replaced by the S92, some six years later. Either one might not be such a smart move. They should re-educate themselves with this blog and ask why similar AD's are coming out again like this older FAA AD 2007-17-05. Obviously there is a problem here.
Everybody forgets the S92 was certified with a gearbox that couldn't last 11 minutes in flight without breaking up and killing people. People have forgotten much about how this came about, no one wants to talk. Most everyone knew however that the drivetrain worked pretty much flawlessly in the UH60/S70 and that sticking it on a big box frame like the S92A was asking for problems, except the accountants running the show at Sikorsky. Maybe the forced redesigns of the MGB put the fear in these people.
Sticking this drivetrain in the S92 would be like Rolls Royce sticking 13 inch wheels on a Corniche and sticking vibration dampers everywhere to improve the ride. On the plus side, you could always pull over on the side of the road and wait for help. But don't blame engineering. They do what they can, with the budgets they are given. Sometimes their budgets are slashed and they're told to let the customer deal with it, just get the thing over the fence.
It's time to fire the inept management and accountants sinking OEM's everywhere instead of laying off underpaid engineers and hangar crews everywhere. Lets
make helicopters great again, like the venerable S61 in the corner, standing by, but never forgotten.
Everybody forgets the S92 was certified with a gearbox that couldn't last 11 minutes in flight without breaking up and killing people. People have forgotten much about how this came about, no one wants to talk. Most everyone knew however that the drivetrain worked pretty much flawlessly in the UH60/S70 and that sticking it on a big box frame like the S92A was asking for problems, except the accountants running the show at Sikorsky. Maybe the forced redesigns of the MGB put the fear in these people.
Sticking this drivetrain in the S92 would be like Rolls Royce sticking 13 inch wheels on a Corniche and sticking vibration dampers everywhere to improve the ride. On the plus side, you could always pull over on the side of the road and wait for help. But don't blame engineering. They do what they can, with the budgets they are given. Sometimes their budgets are slashed and they're told to let the customer deal with it, just get the thing over the fence.
It's time to fire the inept management and accountants sinking OEM's everywhere instead of laying off underpaid engineers and hangar crews everywhere. Lets
make helicopters great again, like the venerable S61 in the corner, standing by, but never forgotten.
Thread, not blog.
Yep, the latest discussion has to do with some bearings in the tail pitch change area. Helicopters sure seem to have issues, be they young, medium, or old.
I don't think anyone forgets that. Like Elephants, plenty of Helicopter pilots have long memories. That tragic loss got a lot of people's attention.
I hear the automotive industry has had that problem as well, but as you said, one can pull over ...
Just FYI, Sikorsky Aircraft is now part of Lockheed Martin (rather than UTC) which leads to "which OEM management and accountants" need the axe in response to that part of your commentary.
How much money you got? 
It looks like the S92 still has issues that haven't been resolved.
Everybody forgets the S92 was certified with a gearbox that couldn't last 11 minutes in flight without breaking up and killing people.
But don't blame engineering. They do what they can, with the budgets they are given. Sometimes their budgets are slashed and they're told to let the customer deal with it, just get the thing over the fence.
It's time to fire the inept management and accountants sinking OEM's everywhere instead of laying off underpaid engineers and hangar crews everywhere.
Lets make helicopters great again,
make helicopters great again,
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like the venerable S61 in the corner, standing by, but never forgotten.
FADEC1, you had me going along until you mentioned the 61.
After 12 yrs service, the numbers tell us that the 92 and 225 represent a new level of rotorcraft safety. One fatal accident each in 12 yrs of intensive civil ops (and one each military/paramilitary) puts them in a bracket apart from their predecessors. One fatal accident is one too many but widely used older types have killed large numbers of people and it has happened without it being put up in lights on the internet.
Hopefully, good work by makers, regulators and operators will maintain and enhance new levels of safety. Let's hope nobody ever dies in new types like the 175 and 189.
If there is an answer to the pressure recently applied to S-92 operations then it is more likely to be a structured re-introduction of the 225 and not a return to older types with dodgy performance.
After 12 yrs service, the numbers tell us that the 92 and 225 represent a new level of rotorcraft safety. One fatal accident each in 12 yrs of intensive civil ops (and one each military/paramilitary) puts them in a bracket apart from their predecessors. One fatal accident is one too many but widely used older types have killed large numbers of people and it has happened without it being put up in lights on the internet.
Hopefully, good work by makers, regulators and operators will maintain and enhance new levels of safety. Let's hope nobody ever dies in new types like the 175 and 189.
If there is an answer to the pressure recently applied to S-92 operations then it is more likely to be a structured re-introduction of the 225 and not a return to older types with dodgy performance.
Most everyone knew however that the drivetrain worked pretty much flawlessly in the UH60/S70 and that sticking it on a big box frame like the S92A was asking for problems, except the accountants running the show at Sikorsky. Maybe the forced redesigns of the MGB put the fear in these people.
In reality, the transmission of the S92 and UH60 are really quite different, particularly with the lube system and top case.
Interestingly enough, a large multi-year redesign of the S92A MGB (known as the Improved Durability Main Gearbox III) kicked off in the late 2000s but has since seemingly vanished.
Sans, two observations re your comments on the 92 box: 1) the reason for connecting it to the UH-60 box was that the similarity of configuration was no coincidence: the underlying design strategy for that box was that it had to be retrofittable to what was hoped to be a growth UH-60* ( now the JMR class ), and 2) there is one rather important difference between the boxes in that the S-92 box has the primary servos mounted on it, thus takes all the servo steady and vibratory loads.
*In fact that is stated in black and white on the Euro Patent paperwork available if you do a search online.
But back to the Fadec1 theory current to this discussion. There have been four rather significant failure events in the past couple of years:
1. AH Gearbox issue/crash(s)
2. SA Run-dry issue/crash
3. AW 609 crash
4. Bell 525 crash
Fadec1 attributes the recent problems to accountants and inept management while giving the engineers a pass. So four major companies suffer the same absence of talent in those areas but none of those issues were affected in part or whole thru human error by human engineers? My observation has been that making helicopters is a team project and a detailed look into the causes behind each of these situations would reveal mistakes or omissions were made similarly. Another associated thought: when I wrote " mistakes ", it wasn't in the sense of someone screwed up and put down 2 + 2 = 3.95. The technical areas involved in these crashes isn't engineering 101 material, so a bit of slack might be afforded the engineering groups.
*In fact that is stated in black and white on the Euro Patent paperwork available if you do a search online.
But back to the Fadec1 theory current to this discussion. There have been four rather significant failure events in the past couple of years:
1. AH Gearbox issue/crash(s)
2. SA Run-dry issue/crash
3. AW 609 crash
4. Bell 525 crash
Fadec1 attributes the recent problems to accountants and inept management while giving the engineers a pass. So four major companies suffer the same absence of talent in those areas but none of those issues were affected in part or whole thru human error by human engineers? My observation has been that making helicopters is a team project and a detailed look into the causes behind each of these situations would reveal mistakes or omissions were made similarly. Another associated thought: when I wrote " mistakes ", it wasn't in the sense of someone screwed up and put down 2 + 2 = 3.95. The technical areas involved in these crashes isn't engineering 101 material, so a bit of slack might be afforded the engineering groups.
There have been four rather significant failure events in the past couple of years:
1. AH Gearbox issue/crash(s)
2. SA Run-dry issue/crash
3. AW 609 crash
4. Bell 525 crash
1. AH Gearbox issue/crash(s)
2. SA Run-dry issue/crash
3. AW 609 crash
4. Bell 525 crash
Big differences between AH (unknown design deficiency), SA (known design deficiency), and 609/525 which were accidents which occurred during experimental flight test beyond the normal operating envelope. Problems with passenger carrying certified aircraft should be kept separate from aircraft in development.
The Sultan
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JD
Big differences between AH (unknown design deficiency), SA (known design deficiency), and 609/525 which were accidents which occurred during experimental flight test beyond the normal operating envelope. Problems with passenger carrying certified aircraft should be kept separate from aircraft in development.
The Sultan
Big differences between AH (unknown design deficiency), SA (known design deficiency), and 609/525 which were accidents which occurred during experimental flight test beyond the normal operating envelope. Problems with passenger carrying certified aircraft should be kept separate from aircraft in development.
The Sultan
The root cause of the S-92 MRGB incident I believe you are referring to was failure of the oil filter housing attachment. Of course, it was still a design problem that should have been caught. I would also argue that the EC225 MRGB bevel gear shaft failures were also something that should not have occurred. Fusion welding (electron beam or laser) of flight critical drivetrain components is a practice questioned by many design engineers in the industry.
I think it is fair to say: In the end it were Engineers that obviously did a mistake. That said the game is not easy for anyone involved. The Accountants and Managers have to make sure the costs stay such that they can sell the product afterwards.
This limits the resources available (Time and Staff) for the Engineering Team. Yet the product has to be a significant improvement in capability and efficiency compared to the predecessors/competitors and may not cost much more. And all this in a heavily matured technology. This means shaving off every ounce. Use of existing components where possible. And finally you need to get the product on the market, i.e. you can't test forever.
Consequences: All manufacturers are bitten from time to time. Which your list proves.
As I understand the oil filter problem, Titanium bolts were used on a component that had to be regularly removed and refitted as part of the mandatory maintenance regime. Whatever the history of Ti use in aviation may be, that approach is very very unwise. Only a matter of time.
As I understand the oil filter problem, Titanium bolts were used on a component that had to be regularly removed and refitted as part of the mandatory maintenance regime. Whatever the history of Ti use in aviation may be, that approach is very very unwise. Only a matter of time.
The stud galling became a real issue because the removal cycles ended up being far greater than anticipated, not simply because of the use of Ti (however the S92 did go through a major weight-loss design optimization effort and it stands to reason that Ti was used here for weight savings).
Supposedly the oil being used was filtered to a lower degree straight out of the barrel than the element size in the MGB filter. This meant the filter popped almost immediately each time oil was changed or altered. This caused the removal and re-installation of the oil filter housing and associated nuts on studs with much greater frequency, greatly accelerating the wear from galling damage.
Due to the MGB lube system design assuming any leak would occur in the oil cooler circuit and not from any of the system behind the cooler bypass valve, when one of those studs on the triangular housing mounting pattern failed there was no way to isolate the resulting leak.
Subsequently the 3 stud pattern was permanently installed and the filter housing was revised to use a 6 stud pattern and split in half with the bottom half adapter never requiring removal.
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As I understand the oil filter problem, Titanium bolts were used on a component that had to be regularly removed and refitted as part of the mandatory maintenance regime. Whatever the history of Ti use in aviation may be, that approach is very very unwise. Only a matter of time.
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Titanium fasteners (like Hi-Lok pins) are commonly used on aircraft structures. But only for applications where they are not normally intended to be removed. They work well in situations where they are installed using carefully controlled procedures.
As soon as the MRGB oil filters were being changed out far more frequently than initially designed for the studs should have been reviewed. Swiss cheese hole #1
As soon as two out of three studs snapped on the Broome flight in July 2008 the studs should have been changed out immediately. Swiss cheese hole #2.
Swiss cheese hole #3 unfortunately took away 17 lives, completely avoidable, more souls would hopefully have survived had the PIC put her down instead of dropping to 800 ft and speeding back at 133 kts for dry land.
I was on that a/c coming back from offshore just 3 days prior to 491 and I lost a lot of good friends and work colleagues that day, IMHO all because the warning signs on the studs were not addressed properly. That is the hard lesson that should have been learned.
Now we have the TRPCS saga back to haunt us after initially rearing its ugly head in 2007. No root cause failure, just increase the awareness and inspection frequency, drop the HUMS IMD threshold from 2.5 to 1.75, update the SGBA algorithm, await the manufacturer's analysis and findings from the inspection/new HUMS threshold failed bearings.
So what is the issue, long-term storage and breakdown of TRPCS seals wet, dry , half-full, hydroscopic/dust particles ingress, supplier material issues, who knows, we certainly don't this side of the fuselage...
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maxwelg2-
Just glanced thru the accident investigation report published by the Canadian TSB again. What I read in section 1.18.3.4, if accurate, was rather disturbing.
"Approximately 58 flight hours before the July 2008 incident, on 09 June 2008, a MGB oil filter bowl mounting stud had fractured during removal of the attachment nut. Because a new stud and the proper tools were not immediately available, after consulting with Sikorsky's local field service representative, CHC carried out a temporary repair, installing a self-locking nut on the fractured stud. The self-locking feature of this nut did not fully engage the shortened length of the fractured stud so a hole was drilled in the nut to lockwire it for security. Although Sikorsky's engineering department was not specifically consulted, no technical objections to the temporary repair were presented by the Sikorsky field service representative."
I find it hard to believe that both the CHC maintenance techs and Sikorsky field service reps considered this to be an acceptable repair procedure. Primarily due to the fact that the proper replacement parts/tooling were not immediately available.
Just glanced thru the accident investigation report published by the Canadian TSB again. What I read in section 1.18.3.4, if accurate, was rather disturbing.
"Approximately 58 flight hours before the July 2008 incident, on 09 June 2008, a MGB oil filter bowl mounting stud had fractured during removal of the attachment nut. Because a new stud and the proper tools were not immediately available, after consulting with Sikorsky's local field service representative, CHC carried out a temporary repair, installing a self-locking nut on the fractured stud. The self-locking feature of this nut did not fully engage the shortened length of the fractured stud so a hole was drilled in the nut to lockwire it for security. Although Sikorsky's engineering department was not specifically consulted, no technical objections to the temporary repair were presented by the Sikorsky field service representative."
I find it hard to believe that both the CHC maintenance techs and Sikorsky field service reps considered this to be an acceptable repair procedure. Primarily due to the fact that the proper replacement parts/tooling were not immediately available.
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riff_raff -
From the same report, however:
1.12.5 “…Testing of the occurrence and exemplar studs and nuts showed that after 13 to 17 assembly cycles, the nut self-locking feature was significantly damaged… “
Curiously, although Cougar CH191 and worldwide fleet maintenance records were averaging around 200 – 220 hours between filter replacements, the CHC VH-LOH had averaged only 72.6 hours over 17 replacements, so the self locking effectiveness may have been lost anyway.
Sikorsky did not recommend renewing the nuts at every filter removal/replacement until September or November 2008, several months after the CHC failure.
So, at least as far as nut (and preload) retention is concerned, it may have been little worse than refitting a worn self locking nut. Neither is desirable but only the improvised repair looks obviously suspect. The studs of both failed, at much the same time, the fatigue damage possibly having been largely done under the original attachment conditions, as later with CH191.
From the same report, however:
1.12.5 “…Testing of the occurrence and exemplar studs and nuts showed that after 13 to 17 assembly cycles, the nut self-locking feature was significantly damaged… “
Curiously, although Cougar CH191 and worldwide fleet maintenance records were averaging around 200 – 220 hours between filter replacements, the CHC VH-LOH had averaged only 72.6 hours over 17 replacements, so the self locking effectiveness may have been lost anyway.
Sikorsky did not recommend renewing the nuts at every filter removal/replacement until September or November 2008, several months after the CHC failure.
So, at least as far as nut (and preload) retention is concerned, it may have been little worse than refitting a worn self locking nut. Neither is desirable but only the improvised repair looks obviously suspect. The studs of both failed, at much the same time, the fatigue damage possibly having been largely done under the original attachment conditions, as later with CH191.