Introduction: Timely access to definitive care has been associated with improved outcomes for injured patients. Air ambulance services have become an integral part of Canadian trauma systems to help provide earlier access to a lead trauma centre (LTC). Multiple factors can lead to non-optimal resource utilization resulting in potential transport delays. The goal of this study is to identify patient, institutional and paramedic risk factors for non-optimal resource utilization for interfacility transfers of injured adult patients transported by air ambulance to a LTC. Methods: Ornge is a paramedic-staffed organization that is the sole provider of air ambulance services from a non-trauma centre to a LTC for the province of Ontario, Canada. This is a retrospective cohort study of all Ornge adult emergent interfacility transports over a 5-year period. Data was collected on patient demographics and clinical status, sending facilities, transport details and paramedic qualifications. Optimal resource utilization was determined based on distance and historical times. A logistic regression model was used to explore patient, provider and institutional risk factors for non-optimal resource use. Results: Between January 1, 2013 and December 31, 2017 a total of 1777 injured patients underwent interfacility transport with Ornge. Of these 805 were identified as having non-optimal resource utilization. Patients who had an optimal resource use were found to be older and mechanically ventilated. Risk factors increasing odds of non-optimal transport included patients transported from a nursing station (OR 1.94), transport with primary or advanced care paramedics (OR 6.57 and 1.44, respectively) and transport between both 0800-1700 and 1700-0000 (OR 1.40 and 1.54, respectively). The median delay to arrival to receiving facility if a patient had a non-optimal resource use was 40 minutes Conclusion: We were able to identify several factors resulting in non-optimal resource utilization. We believe that nursing stations as a sending facility and type of paramedics crew transporting patients resulted in non-optimal resource utilization mainly due to these patients being of lower acuity and this affecting their triage. However the timing of day is more likely to be a resource availability issue and something that can be further studied and potentially improved.