ZS-X,thanks for the pics of the filter; I wondered if the `muffler` had any form of filtration in it or not,but it seems unlikely. XW276 was a development aircraft,as you can tell by the doors and the roof canopy,We did a lot of the initial handling trials for radios,roping,winching,flares,paratrooping,and general handling up to `73,then it got `left behind` as it couldn`t be modified to production standard.If you look at `Rotorheads around the world ` page 15 ,there`s a pic of XW846,dressed up in skis and icing trials gear in Canada. That was the last Gazelle I flew,on 23Dec `76...but I`m open to offers !!!!