We were about 15 minutes into a quadbike club event when we needed to dig part of a track for safety. Three of the group of five had traversed the hazard when we were alerted to a rider collapsing. We returned back over the hazard to find our collegue on the ground. He was unresponsive. Two people quickly started CPR whilst I set off the PLB and attemped to get cell coverage. First responders were carried in by quadbike and they continued resusitation until the helicopter arrived with advanced EMS onboard. Unfortunately Dave did not survive and was declared at the scene. Whilst Dave did not servive, first responders were on the scene within 45 minutes and the helicopter about 20 minutes later. So we were confident that everything had been done in an effort to revive him.