Just to add a few points on the HUMS installation on the AW139. We've found it to be a very very useful tool in troubleshooting vibes on the machine. We download after each days operation (although we have had some customers ask for download after each flight) and the information we gain from the HUMS groundstation is excellent in its depth and in it's easy to use format. It has pinpointed TR driveshaft problems not only at the MGB end but also at the IGB which turned out to be hardened grease and a worn adapter. It has also alerted me to an unreported inflight engine shutdown after a training flight error, which led to the engine being removed as a precautionary measure. Agusta and GE offer a one week course in Milan (maybe elsewhere now) which I found very informative and recommend to other operators. Most of the problems we have had with the sensors have resulted from inadvertent damage to the cables incurred during maintenance, but again the data available and the codes available in the manual can usually pinpoint the problem. As far as the logic used by the system, it uses the tried and tested RADS logarithms to calculate the adjustments and predictions. In over 3000 hours we have found it to be very accurate.
As far as tuning the 'nodal' tuning type weights under the floor, this can also be carried out using a tensiometer, which reads in hertz, similar to the one used to test the airconditioning belts, this worked for me. If the weights aren't doing the trick as far as 5 per revs are concerned, it might be time to fit the MVA which generally gets the 5 per revs down under .3 and gives a very smooth ride once the 1 per revs are tuned. We did find one machine had some wild M/R adjustemnts including inboard tab settings from the factory giving it a persistent track split, but by returning the M/R to nominal and carrying out a few test flights, we got it back in nicely with one weight move, one PCL adjustment and one small tab move. The MVA will do the rest and does not require adjustment. Again the ground station gives you the opportunity to play around with editing your moves and looking at the possible results meaning you canminimize the moves you make to get the best result.
Happy to pass on more info if anyone is interested. Cheers.
