As with anything else, HUMS is a question of money.
Data collection, i.e. "Just a few accelerometers" and "some time frequency analysis software" Sure, cheap as chips. The key though is not just data acquisition, but processing, its what you do with it that makes all the difference.
For example, vibration as we know does not do your aircraft any good, so to minimise, first up, we make sure our rotor generated vibrations are at the absolute minimum, so you need RTB.
Next Transmission, do these aircraft suffer much in the way of defects? If yes, then you need a good monitoring technique, if not, then is it worth the investment?
Engines? The engine has been around for a long time, not the smoothest, but a pretty stable platform, so worth the cost of an engine monitoring unit? The fan can and does generate a lot of vibration, so a bit of fan balancing would be nice.
Now driveshafts? this is a good one on the robbies, do you want to monitor shaft vibration? I would suspect so, at various locations, not least around the drive belt assembly.
This is getting deeper and more expensive by the minute.. a good method of saving money is better maintenance planning, and spares provisoning. Reducing vibration will save you in the long term on spares provisioning through reduced wear rates, but better maintenance planning will reduce your downtime. So early warnings of a potential fault can allow this, so I guess we need all that engine and transmission data after all.
Component vibration level trending and fleet averaging is the simplest method of establishing a baseline, from which you can determine if something is going amiss, alternatively, the manufacturer can advise on vibration thresholds. Also are you going to sift through the data on a flight by flight basis or will you require software to spot threshold exceedances? You will also need a means of data archiving and storage.
It can be an expensive business, as no doubt Nick, Shawn and others will tell you. You need to be clear about what you want to achieve within your budget, and then decide if its actually financially viable. On a Robbie, I'm not so sure, but then from a safety point of view, I do believe that all helicopters should benefit from HUMS and what it can do, sadly I don't fix the prices, or I'd give it away.
Good luck.
