Take a look inside Qantas' 'secret' archive as it celebrates 90 years of international flights

Ninety years ago today the very first excited passengers climbed aboard Qantas' inaugural overseas flight.

The plane, which had wooden wings and a steel fuselage covered with fabric, took off from Brisbane, bound for Singapore.

The journey aboard the DH86 on April 17, 1935, was a "major breakthrough" at a time when it took five weeks to get to the UK by boat, experts say.

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It took three and a half days to get to Singapore, and from there passengers could fly on to London. And it was quite an experience.

"They didn't fly at night, they stopped overnight, stayed in hotels," David Crotty, curator of the Qantas Heritage Collection, tells 9Travel.

"There were about 17 stops along the way, so it was a bit of a marathon."

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Qantas has been flying internationally for 90 years

"You were flying pretty low, there was no cabin pressurisation and no oxygen, so you couldn't fly higher than 10,000 feet anyway. The benefit is you could see where you were going."

The plane, which could hold up to eight passengers, also carried cargo including mail. And there were in-flight meals, of sorts.

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"There was no in-flight catering, although the co-pilot used to hand out sandwich boxes," David says. "You could also smoke - but you couldn't smoke pipes or cigars."

Imperial Airways, the forerunner to British Airways, took passengers onwards from Singapore to London, a mammoth 12-day journey with multiple stops.

That first flight carried only two paying passengers, a major in the Queen's Coldstream Guards and Lady Mountbatten, an aristocrat who went on to become the last Vicereine of British India.

That's because it cost around an average years wage for a return ticket, David says. It cost around 500 pounds at the time.

"It was the equivalent of a Chevrolet motorcar," David says.

A few years later, Catalina flying boats from Rose Bay in Sydney Harbour took over the route.

But those first flights paved the way for the airline, which started delivering mail in the outback, to become a major international carrier.

It's now the world's oldest continually operating airline and bosses are now pioneering another first.

Project Sunrise will see the first non-stop flights between Sydney to London and New York City from next year.

Inside the secret Qantas archive near Sydney Airport

Secrets of those early flights and other milestones in Qantas' history are kept in a private archive in Mascot, near Sydney Airport.

From parts of engines to timetables, pieces of aircraft instrument panels and rails of old uniforms, it's packed with thousands of items, but closed to the public.

"The collection's not just the history of Qantas, it's the history of aviation, the history of fashion, the history food from the menus, political history, social history, military history - it's the history of Australia," David tells 9Travel.

Documents from the time Qantas started in 1920, as Queensland and Northern Territory Aerial Services, in Winton, Queensland are preserved.

There are also copies of Double Sunrise certificates which were given to passengers on the record-breaking Perth to Ceylon route from 1943. At up to 28 hours it still holds a record for the longest non-stop service.

At a time with no GPS, the plane was steered using celestial navigation was done via the stars and the sun using an instrument call a sextant.

Model planes in the collection also show the development of aircraft, including the pioneering Lockheed Constellation, which had first class at the back because it was quieter.

Business class hadn't been thought up yet. In 1959 jets arrived, shortening flight times and lowering prices.

Travel became open to more Aussies from the 1970s, when the Boeing 747, known as the jumbo, arrived.

It had the lavish first class Captain Cook lounge on the upper deck.

The museum even houses a model Concord painted in the Qantas livery.

But the supersonic jet never ended up suiting the Australian market, partly because the sonic boom meant it couldn't fly over land.