A helicopter instructor reported an NMAC with a fixed wing aircraft at BDN.

Narrative

I was with a student in a helicopter. After landing from traffic pattern work; we exited the runway at Bend Municipal Airport at B3 taxiway to do some hover practice. After 10 or 15 minutes of hover practice we needed to get back across the runway to park. We hovered to the hold short lines at B3 and after hearing numerous airplanes taking off/landing; we set the helicopter down at the hold short lines to wait for an opportunity to cross. While we were sitting there; I saw another aircraft holding short at A1 for Runway 34. We also heard a call from a company helicopter saying they were on a practice instrument approach to 16. When there was a break in the traffic; we made a radio call saying that we were crossing the active Runway 34 from B3 to A3. After that; we picked the helicopter up and both my student and I looked left at final; then right; and then left again. We observed the other aircraft still holding short at 34; and since no more radio calls were made; we hovered across the runway at a height of 3 FT. As we were passing the hold short lines at A3; we heard a radio call from an airplane talking about a near collision that had just occurred. I looked back behind the helicopter and saw an airplane about 40-50 FT above ground that looked like it had just taken off. Neither my student nor I ever heard a radio call saying they were going to take off and we both visually cleared the runway before we crossed. The pilot of the other aircraft has reported that he had to dive down to fly under my helicopter. There is no possible way a plane flew below us; since we had maintained a 2-3 foot hover (normal helicopter procedures) the entire time crossing the runway. After we got back; I talked to the other helicopter pilot who was on the practice instrument approach at the time and he also verified he had heard our call announcing our intentions to cross the active runway from B3 to A3. Both the plane and us could have made better or more radio calls announcing our intentions to cross or takeoff on the runway. Even though the airport is in Class G airspace; all pilots should use radios to announce their intentions. This could reduce near misses and help improve the aviation community.