Will self-flying planes transform the skies?

Over an alfalfa field in California's San Joaquin Valley, a small crop-spraying plane is flying scarily low to the ground. There's little risk to humans though, as the plane is pilot-free.

"We can actually go lower than a human pilot can," says Russ Marotzke, as the aircraft skims over the crop.

Flying lower means less spray drift and therefore less chemicals are needed than in conventional manned crop-dusting, he says.

The pilotless plane belongs to Pyka, where Marotzke works as a flight test engineer.

Based in a converted Second World War hangar overlooking San Francisco Bay, the start-up makes self-flying aircraft without cockpits, designed either to spray crops or deliver cargo.

It is among a small group of companies racing to bring autonomous fixed-wing aircraft into commercial service.

Flying urban air taxis, so called electric vertical take-off and landing (eVTOL) aircraft, have captured much of the attention around autonomous aviation.

But a quieter race is also under way to deploy self-flying planes, first for jobs like crop spraying and cargo delivery – and eventually, many of their makers hope, carrying passengers too.

"A fully scaled, ubiquitous passenger operation is the holy grail," says Michael Norcia, Pyka's co-founder and CEO, who envisions a large fleet of minibus-capacity Pyka planes ferrying passengers up and down the US east and west coasts.

I've come to one of Pyka's crop-sprayer test sites, about 80km (50 miles) east of the company's factory and reached by a bumpy dirt road.

Today, Marotzke and a colleague are trying out a software update on a demonstration aircraft.

About a dozen Pyka aircraft are already in Brazil where they are used to spray crops such as cotton and soybeans, work previously carried out by human pilots.