As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE ON THE GROUND GETTING READY TO LIFT OFF REX HELIPAD, THE CREW STATED THERE WAS A SMELL IN THE BACK. SHORTLY AFTER, THE SMELL INTENSIFIED ENOUGH FOR THE PILOT TO SMELL IT IN THE COCKPIT FOLLOWED BY THE CABIN BEING FILLED WITH SMOKE COMING OUT OF THE AIR VENTS IN THE BACK. PILOT IMMEDIATELY SHUT OFF THE AIRCRAFT AND CREW WERE CLEARED OUT THE AIRCRAFT. PILOT TOOK AIRCRAFT OOS AND MECHANIC WAS CALLED.