Then the number of flight crew fell to two when the Boeing 757 changed the way cockpits were designed in the 1980s. Now, jetmakers are studying what it would take to go down to a single pilot, starting with cargo flights.

The motivation is simple: saving airlines tens of billions of dollars a year in pilot salaries and training costs if the change can be rolled out to passenger jets after it is demonstrated safely in the freight business.

But with the disappearance of Malaysia Airlines flight MH370 and a deliberate crash by a Germanwings pilot in the last few years, earning public trust and ensuring safety is critical. The issues loom large as single-pilot flying concepts are fleshed out at the Singapore Airshow this week.

“We are studying that, and where you will first see that is probably in cargo transport, so the passenger question is off the table,” Boeing research and technology vice-president Charles Toups said of one-pilot operations.

It would take a “couple of decades” to persuade passengers to take a single-pilot jet, he said, adding that gaining public support for the concept would be a step-by-step process starting with proliferation of self-driving cars. Boeing co-operates with General Motors to develop technologies for autonomous flight.

Singapore Technologies Engineering’s ST Aerospace demonstrated to delegates how a cockpit could be modified for one pilot when the firm converts passenger jets to freighters.

“The interest is global,” ST Aerospace’s chief operating officer, Jeffrey Lam said. “I think some [cargo operators] are watching each other; quite certainly if one jumps on board, you would expect the others to not want to fall behind because there’s a lot of cost savings here.”

Although some small business jets can be flown by a single pilot, commercial jets carrying passengers and cargo require two pilots at the controls. That protects against the potential incapacitation of one pilot and helps with the cockpit workload.

After the Germanwings crash in 2015, in which a disturbed pilot locked himself alone into the cockpit, and crashed the aircraft into the Alps, regulators worldwide introduced rules requiring two people in the cockpit at all times.

But such rules were lifted two years later when they were found to add little to security while introducing new risks.

For now, regional cargo flights seem the most realistic area for single-pilot flying.

Kevin Shum, director-general of Singapore’s Civil Aviation Authority, said flight technology was advanced enough to create a one-pilot cockpit in as little as five years.

“But it is a question of the human factors,” he said, citing incapacitation, distraction and fatigue as the biggest problems that would give regulators pause for thought. “That I think will probably take a bit more time to work through.”

Airbus and Boeing jets are designed for two pilots, and taking one out of the equation would need a revamp of the flight deck. More automated systems would be needed, as well as a way for controllers on the ground to take over if needed.

A Nasa study published in September was not encouraging.

US airline pilots tested solo in Boeing 737 simulators found the workload “unacceptable” even in normal flight conditions, let alone when something went wrong.

The study projected the prospect of having one of two pilots take a nap while the other sat at the controls as being more plausible, suggesting it might be possible for airlines to reduce long-haul crew numbers in the future. Some ultra-long flights can have five pilots on board to take turns between flying and resting.

Although human error is estimated to cause about 60% of crashes, there have also been situations where trained pilots have saved planes from disaster, such as the famous “Miracle on the Hudson” Airbus A320 water landing in New York’s Hudson river in 2009.

While there is little data on the number of times human intervention has saved planes, pilot unions say safety is paramount, even in cargo operations.

“Having a pilot to load-share with you in command of an airplane is invaluable,” said Australian Federation of Air Pilots president David Booth, a pilot at Virgin Australia . “We are not at all interested in these one-pilot concepts. They are driven only by costs.”

Qantas Airways chief executive Alan Joyce said the airline, which had five pilots on board to help an A380 damaged by an engine failure to land safely in Singapore in 2010, did not have plans to take pilots out of the cockpit any time soon.

“Certainly there is still a public perception issue and I think there will continue to be for some time about being too automated when it comes to commercial aircraft,” he said.

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