Before electric VTOL air taxis have a chance to start changing modern life as we know it, any company that wants to manufacture one has to go through the extremely expensive and exacting process of commercial aircraft certification with one or more flight authorities, during which many different parts of their business will have to meet the same stringent safety and process standards that, say, Boeing does when it's making an airliner.The two key flight authorities in question are the United States Federal Aviation Authority (FAA) and the European Aviation Safety Agency (EASA); achieve certification with these two and your aircraft are likely to be accepted worldwide. But this is a huge mountain to climb – we've heard estimates as high as a billion dollars to get a single eVTOL aircraft fully certified and into commercial use.