Australian airline Qantas has announced plans to test flight routes that would be the longest in the world.

The airline announced Thursday that it will run the tests along two routes – one from New York to Sydney and one from London to Sydney.

The test flights will not be open to regular passengers. A select group of people – mainly Qantas employees – will board the planes. Each trip will carry a maximum of 40 people, including the flight crew, in order to keep the plane's weight low enough that it can make the journey without needing to refuel.

The trips are expected to take approximately 19 hours, depending on weather conditions – or about 15 minutes longer than the flights Singapore Airlines restarted last year between Singapore and Newark, N.J.

Everybody on the plane will be monitored by medics and scientists, who will be tracking how the ultra-long flights affect pilot and passenger health, including sleep patterns and food consumption.

"Ultra-long haul flying presents a lot of common sense questions about the comfort and wellbeing of passengers and crew," Qantas Group CEO Alan Joyce said in a statement.

“For customers, the key will be minimizing jet lag and creating an environment where they are looking forward to a restful, enjoyable flight. For crew, it’s about using scientific research to determine the best opportunities to promote alertness when they are on duty and maximize rest during their down time on these flights."

The test will comprise three flights – one apiece in October, November and December – using new Boeing 787-9 aircraft that would have otherwise flown empty from Seattle to Australia during their delivery.

Joyce said he has given the airline until the end of the year to assess the results and determine whether it should continue to pursue its goal of eventually offering regular, non-stop flights to London and New York from Sydney, Melbourne and Brisbane.

No airline has ever flown directly from New York to Sydney, according to Qantas, while the only direct commercial flight ever between London and Sydney was a special trip organized by Qantas itself in 1989.