The noise reduction mod for the Power is a redesigned tail rotor, which significantly changes the noise profile, as well as lowering the EpNDb. A modified Power has a noise signature more akin a JetRanger without the two blade beat, as well as being some 6Db quieter on a 1000ft overflight.
When Sydney was to get a helipad, a lot of trials were done to allocate a landing allowance per type, based on the noise footprints. The A109 was the worst culprit of those tested, and one A109 landing equated to (IIRC) about 6 JetRanger landings
Peter,
Whilst the (unmodified) Power can be noisy, your assertion that it is heard for 6 minutes is remarkable, if it is at normal cruise speed (145kias). That means you would be listening to it for nearly 15 track miles: can I borrow your ears for my next audio assessment ?
