I think that trying to turn HUMS from a monitoring system into a warning system may be too difficult. It was always designed to try and pick up trends in component's characteristics and then as experience was built up look for trigger points to replace that component.
http://www.pprune.org/rotorheads/522...ml#post8011027
In essence HUMS moves maintenance away from reactive based maintenance to pro-active maintenance. So in the end the HUMS software is designed to maintain the 'health' of a harmonic signature...not the imminent failure of the component.
FWIW, the US Navy has been working with HUMS in their SH-60/S-70 fleet for some years (I think about two decades). One of the frustrations I have heard from maintenance departments is the number of false positives they encounter. (And some of this may be software driven ... ). Better safe than sorry, but their experience is why the above quotes need to be understood. It's not quite a "caution" or "warning" light generating system, to date.
UKpax
Are there any helicopters that have a system to slow descent in the event of a gearbox or rotor failure?
All do, it's called "pilots" for a gear box failure. Use the flight controls to get the craft down to earth in a controlled manner. When the tail rotors fail, one can usuall auto down or do a power reduction and ditch ... when the main rotors fail or brake (leave the aircraft while at flight RPM) in flight, you are likely dead at that point. (Massive CG shift and uncontrollable rotor disk).
Given the air industry builds redundancy into their critical systems, its always struck me that the helicopter gearbox/drive shaft is a system where redundancy seems to have been deliberately ignored - I presume there's no practical solution, is there?
The design engineers increase/beef up safety factors for such components. Design has to be for "infinite fatigue life" on many more components than fixed wing. Failures are uncommon for that reason. Also, helicopter maintenance is very inspection intensive. (Recalling preflights of the dozens of torque striped nuts on various helicopters over the years ... )
UKpaxman
I guess the point I'm making is that I can't think of another form of civilian transport that places 100% reliance on something as complex as a gearbox with no redundancy in the event of a catastrophic failure.
That's why safety factors in gbx designs are significant. (Generous)
I think you will also find, in most cases, that in a reasonably well maintained aircraft, that failures which will cause a gear box to go completely TU typically give off warning signs before all goes south. (Vibration, noise, oil temp/pressure rise, lights flashing ... ) You get a chance to land/ditch before it all turns into horribly deformed metal.
I also think that as even the best assembly may develop problems, if I were required to sit in one of those busses to go to my work, I would be a lot happier if the flotation gear was improved.
colibri: liked your post. On that point ... someone a few pages back noted that SOP's where he works called for floats armed anytime flying over water. Seems a wise SOP to me, particularly when carrying passengers.
colobri
Now to my final point; an anology. You're driving your Mondeo along a road and come upon a serious accident involving another Mondeo. Or maybe it wasn't even you, but a family member of yours who told you about the accident. Either way, does it make sense to immediately get rid your Mondeo and join a clamour for all Mondeos to be recalled, before anyone knows the cause?
No, it makes no sense, but one must never forget that group IQ tends to be inversely proportional to group size.
cyclic
Unfortunately, in order not too scare the living daylights out of the work force, the dunker is a very gentle affair in a warm swimming pool. I can assure you the military version is much more realistic but half the workforce wouldn't pass the course. Where do you draw the line of realism against risk?
Well said.
Mitchaa
Double engine failure just does not happen (Unless it ran out of fuel) so kind of rules that one out too.
Consider the possibility of fuel contamination ... no idea on this one. ... though usually when the lines get clogged you see a few lights and bypass indications before all goes south, in the heilcopters I am personally familiar with. Not sure how the 332's systems approach that.
HC:
You made a point about a model of helicopter where engines fail toward Idle, which I presume is a feature of the ECU/DECU. (If I guessed that wrongly, please correct me). That seems to me a very odd design feature.
If an ECU / DECU fails toward high power, you can control NR with incr pitch and then (with a good crew) your non-flyer can cut the DECU / ECU out via cockpit switches or engine control options ... depends on model, I suppost. (I am most familiar with S-70 class and its engine controls). This would hopefully leave one some version of manual fuel control, and you always have some NR in flying range going for you.
If it fails to low power, or both do, you droop. That can be bad three ways:
lift loss
controllability change
typically generators may kick off making for more trouble.
From what you posted, and being not familiar with the aircraft in question, I don't understand this design decision.
What's the upside of that approach?
(Failures that are "graceful degradations" being preferred to "suddenly it's all gone" from a design point of view)
Oil Company points finger at the Operators.......Operators point fingers at Oil Company. Pilots point finger at Company.....Company points finger at Pilots. Everyone points finger at Authority.....Passengers Union points fingers at everyone else......and the Authority eats the pies and collects a nice Pension.
Thank you, SASless.
Just waiting for Benny Hill to run by, pursued by a few scantily clad lovelies ...