THE ACFT COLLIDED WITH POWERLINES WHILE CARRYING PASS'G ON A SIGHTSEEING FLT THROUGH A CANYON. THE WIRES ACROSS THE CANYON WERE EST TO BE 1700 LONG WITH HEIGHT AGL UNKNOWN. THE WIRES WERE UNMARKED AND WERE 1/2 IN DIA ALUMINUM. ONE OF THE PASSENGERS WAS FILMING THE SCENERY DURING THE FLT AND THE PLT LATER SAID HE THOUGHT THAT A BATTERY PACK FOR THE CAMERA HAD INTERFERED WITH THE COLLECTIVE CONTROL DURING HIS ATTEMPT TO AVOID THE POWERLINES. THE PASSENGER SAID THAT ALL THE EXTRA PHOTO EQUIPMENT WAS IN A BAG IN THE BACK COMPARTMENT. SOME CAMERA EQUIPMENT WAS FOUND OUTSIDE THE ACFT AFTER THE ACCIDENT. THE BATTERY PACK WAS LATER PLACED BY THE COLLECTIVE CONTROL TO TRY TO DUPLICATE THE EVENT. THE ONLY WAY INTERFERANCE COULD HAVE OCCURRED WOULD BE TO HAVE THE PACK ON EDGE & FULL AFT NEAR THE COLLECTIVE CONTROL PIVOT POINT. THE EQUIPMENT FOUND OUTSIDE THE ACFT WAS PLACED INSIDE BY RESCUE PERSONNEL DURING THE RECOVERY OPERATION. THE PLT ALSO REPORTEDLY SAID 'HOW DID THAT HAPPEN' INDICATING HE NEVER SAW THE WIRES.