INTRODUCTION: In the United States, between 1995 and 2013, night-time visual flight rules (VFR) Helicopter Emergency Medical Service (HEMS) fatal accidents mostly encountered adverse weather, and pilots with <6 yr of HEMS experience showed higher likelihood of a night operational accident. One adverse weather indicator is cloud-ceiling likelihood indicated by temperature dew point spread (TDPS). This study investigated the relationship between TDPS and HEMS pilot years of experience. It was hypothesized pilots with <6 yr HEMS experience were associated with fatal outcomes encountered at lower TDPS.METHODS: Between 1995 and 2013, 32 single pilot night VFR HEMS fatal accidents occurring in the United States, caused by controlled flight into terrain or loss of control, were analyzed. Using Federal Aviation Administration weather guidance, the 0–4°C TDPS was selected as an indicator of cloud ceiling. Each flight’s TDPS was analyzed with pilots’ HEMS domain task experience.RESULTS: There were 27 flights which entered the 0–4°C TDPS range; 20 (74%) were significantly associated with adverse weather. A significant negative linear relationship was found between TDPS of each mission and years of pilot HEMS experience (r = −0.423, P = 0.028). Pilots with <6 yr of experience were significantly associated with fatal outcomes (P = 0.049).CONCLUSION: Pilots’ incremental years of HEMS experience were associated with a TDPS decrement. Fatal outcomes were over nine times higher for pilots with <6 yr of HEMS experience in night VFR operational accidents in those conditions. Interventions for <6-yr pilots are recommended during experience building to prevent likelihood of operational accidents.Aherne BB, Zhang C, Chen WS, Newman DG. Pilot decision making in weather-related night fatal helicopter emergency medical service accidents. Aerosp Med Hum Perform. 2018; 89(9):830–836.