To make a delivery in the remote town of Hana on the Hawaiian island of Maui, it’s easier to fly a small plane than drive along the switchback-filled road that connects to the main part of the island. Later this year, the route may become the first place that a commercial airline flies an electric plane.

Ampaire, an L.A.-based electric plane startup, plans to begin its first tests of a Cessna retrofitted with an electric drivetrain in the first half of this year. Then it plans to partner with Mokulele Airlines, which flies short routes in Hawaii, for further tests. The route to Hana is one potential test location. By 2021–as soon as the company gets FAA approval–passengers will be able to book a flight on one of the planes.

Unlike some other startups working on small electric planes, Ampaire isn’t launching with a plane designed from scratch. “The core of the mission for our company is to build practical and compelling products that bring meaningful solutions as quickly as possible,” says Kevin Noertker, cofounder and CEO of Ampaire.

While a new-build airplane might take $200 million dollars and 10 years of development and certification, he says, retrofitting costs tens of millions of dollars and only a few years. “That’s because you’re using a plane that already has the approvals from the regulatory agencies, and you’re just modifying those existing approvals.”

The company modified a plane with two propellers; they replaced one propeller with a fully electric drivetrain, making it possible to fly a 100% electric flight. But one of the propellers will remain on the plane with the original fuel system as a backup. “Especially during our engineering flight test, where we want to expand the envelope of how we fly and the amount of power we’re using, we’re able to do so without any fear of safety of flight risk, because we’ll always have that combustion engine,” says Noertker.

For airlines, shifting to a fully electric plane can potentially save 75% to 90% of the energy cost for a flight, depending on the fuel and electricity prices in a region. Because electric planes also use fewer parts, they also may reduce maintenance costs by 25% to 50%. In Hawaii, the company hopes to prove out those projections for the first time. By cutting cost, electric planes could become a viable alternative to driving for some short routes–and bring back commercial flights to more regional airports. “What we’ve seen in the airline industry is that the number of airports that are served by commercial aircraft have been significantly decreased over the last few decades,” he says. “That’s because it’s just not economical to fly to most of these small regional airports.” There are around 5,000 regional airports in the U.S., but fewer than 1 in 10 are used commercially now–the rest are just private flights.

The startup may be the first to have electric planes in commercial use, though others are poised to quickly follow. Eviation, an Israeli-startup, aims to bring a fully-electric plane to market by 2021. Zunum Aero, a startup backed by Boeing and Jet Blue, hopes to deliver its first hybrid-electric planes in 2022. Siemens and others are also working on small electric planes. Wright Electric is working on a larger, 180-passenger plane that may come to market in 2027. These timelines are “relatively ambitious,” Noertker says, so it’s possible that there may be a larger gap of time between the introduction of the retrofitted planes and the new models.