# Advanced Air Mobility: Opportunities and Challenges Deploying eVTOLs for Air Ambulance Service
## 4 Analysis and Findings
### eVTOL and Hybrid Aircraft Dispatch Reliability and Market Potential  
The authors used the study findings to assess the suitability of eVTOLs and hybrid aircraft for the existing rotary-wing aeromedical market using demand modeling. To do this, the authors established a dispatch reliability model to calculate the probability of events for which an eVTOL or hybrid ambulance was unavailable. The dispatch reliability is calculated by the total number of events in which an air ambulance is available divided by the total number of events where an air ambulance would be dispatched if available. The demand model for aeromedical service estimates the effective number of transports required compared to those that could be performed, hourly demand distribution, and dispatch reliability for modeling for different scenarios (Figure 9). As previously noted, with the exception of a battery swapping scenario, the increase in total call time for eVTOL aircraft decreased the number of transports these aircraft could complete, increasing overall costs. To achieve a comparable cost level to existing rotorcraft, eVTOLs would have to perform a greater number of transports. However, hybrid aircraft and eVTOLs with battery swapping capabilities reduced total call time, making them a potentially more attractive economic replacement for existing rotorcraft. For modeling purposes, the authors assumed an average weekly distribution across all bases in the U.S. On average, demand was generally lowest between 12 AM and 6 AM, and typically peaked between 12 PM and 6 PM each day of the week. The late night accounted for approximately 10% of total aeromedical trips compared to 40% during the mid-day period. Finally, the authors estimated dispatch reliability by calculating the probability of events where an eVTOL or hybrid aircraft would be unavailable. Figure 8: Comparison of total call time for various aircraft and scenarios. Figure 9: Demand model for air ambulances. Aeromedical transport follows established dispatch protocols to maximize the safety and benefits of air ambulances. Common factors that influence a dispatcher's use of an air ambulance include the need to minimize patient transport time to a medical facility, a patient requiring time critical care from a medical facility that is further away, and a patient requiring critical care support not available through ground ambulances. Dispatchers may also opt for an air ambulance when an area is not appropriate for ground transportation or lacks EMS coverage. However, in order for a dispatcher to use an aeromedical service, passenger weight must be within allowable limits, there must be a landing facility at or near the destination medical center, and both current and forecast weather conditions must be suitable for the air transport. Because eVTOLs require an increased number of transports to become economically viable, an increased number of transports also increases the probability that an aircraft is not available for other calls, reducing the dispatch reliability for eVTOLs. The probability model estimates a dispatch reliability of approximately 90% for eVTOLs, which is considerably lower than the desired industry goal of approximately 99% (Figure 10). However, when distributing demand on an hourly basis, the model found that the dispatch reliability of eVTOLs drops to 10% between 12 AM and 6 AM compared to 100% dispatch reliability for rotary-wing and hybrid aircraft. As noted earlier, to achieve the same level of dispatch reliability as rotorcraft, eVTOLs need to reduce its total call time by 145 min. Therefore, to achieve this, reduced charging times would be necessary to reduce the time required for eVTOLs to return back to service for another mission. One way to achieve reduction in charging times would be to use super chargers with higher power available. As indicated earlier, this research uses 125  
Figure 10: Dispatch reliability on air ambulances. kW chargers that leads to charging times of 200 min.