Fully electric planes, while promising, are limited by available battery technology.

Batteries cost less and pack more energy into a smaller package than they did a decade ago, but they're still too heavy to allow planes to fly long distances or carry heavy loads.

They do work, however, in low-flying air taxis for short runs across a city or to the airport.

These new electric vertical takeoff and landing (eVTOL) aircraft are getting a lot of attention on Wall Street, but they won't be widely available until around 2035, according to a Deloitte analysis.

Yes, but: For medium distances of 50 to 500 miles -- the city-hopping routes ignored by hub-and-spoke airlines -- hybrids offer a practical solution that can be ready in just a few years.

UBS, the Swiss investment bank, forecasts a $178 billion market for hybrid-electric aircraft.

Driving the news: Surf Air Mobility, a regional air travel service, said this week it would acquire Ampaire, a developer of hybrid electric powertrains for aviation.

Surf Air co-founder and CEO Sudhin Shahani called Ampaire's technology a step toward "the next great shift in air travel: sustainable aviation that's accessible to everyone."

For now, the company's plan is to upgrade existing turboprop aircraft with Ampaire's hybrid technology on short, regional routes while the industry works toward fully electric aviation for all trips.