# Advanced Air Mobility: Opportunities and Challenges Deploying eVTOLs for Air Ambulance Service
## 3 Methodological Overview  
The authors conducted a literature review of air ambulance service characteristics, operational assumptions, and potential applications of novel aircraft. Between Summer 2017 and Winter 2019, as part of a National Aeronautics and Space Administration (NASA) market study, the authors established a study advisory group (SAG) to solicit feedback on key assumptions from more than 50 public and private sector thought leaders to inform this research. SAG members included senior professionals and subject matter experts from NASA, the FAA, the National Transportation Safety Board (NTSB), the North Carolina Department of Transportation, New York City, the city of Los Angeles, Los Angeles World Airports, the International Civil Aviation Organization (ICAO), and numerous manufacturers, startups, and academic institutions. Public sector participants included directors of the FAA's Aviation Plans and Policy Office, the Office of International Affairs, the Unmanned Aircraft Systems (UAS) Integration Office, and a former NTSB chairman. Manufacturers and startups representing a diverse set of planned airframes were also included as part of the SAG. Using input from the SAG, the authors developed a five-step process to analyze the air ambulance market. Collectively, these five steps (described below) included calculating key business and operational metrics, such as number of flights, potential revenue, operating costs, transport volumes and distribution, and infrastructure availability (e.g., number, location, and capacity of hospitals and other medical facilities with helipads/vertipads). Step 1. Preliminary Scoping  
The first step included defining operational concepts for the air ambulance use case. CMS service level, regardless of ground or air ambulance, consists of six key temporal phases: (1) dispatch time; (2) chute time; (3) response time; (4) time on scene; (5) transport time; and (6) return time. 1. Dispatch time is measured from the time a telephone dispatcher receives a call until they dispatch an ambulance. 2. Chute is the time from when a call is dispatched to the time an ambulance begins to travel to the location. 3. Response time is measured from the time an ambulance is en route until the ambulance reaches the scene. 4. The time on scene is measured by the time a unit arrives on scene to the time a unit departs the scene. 5. Transport time is measured from the moment an ambulance leaves the scene until a patient arrives at their destination. 6. Return time is the time it takes for an ambulance to leave their destination and return to service. Collectively, the entire time period from dispatch to placing an ambulance back in service is referred to as total call time. The authors assumed that dispatch, chute, and time on scene are fixed time intervals not affected by the aircraft type. Therefore, only response time, transport time, and return time can be improved through aircraft enhancements. Each of these temporal phases and times measured in minutes are shown in Figure 1.  
Step 2. Inventorying Operational Assumptions  
The second step involved developing operational assumptions and modeling key performance metrics such as crew size and flight profiles. To do this, Section 3.1 outlines more specific operating assumptions that were used as part of Step 2. Step 3. Baseline Calculations  
Next, the authors calculated the cost of emergency medical service for different aircraft types proposed to serve the air ambulance market. Each cost, such as capital, maintenance, batteries, electric charging, vertiports, and personnel were individually modeled. Section 3.1 outlines the specific process used to formulate the baseline calculations for each aircraft type. Step 4. Monte Carlo Sensitivity Analysis  
Fourth, the authors performed a Monte Carlo sensitivity analysis simulating 10,000 randomly generated air ambulance missions. Section 4 summarizes the methodology used to conduct the Monte Carlo simulation. Step 5.