The world's most mysterious airline is advertising for a pilot to fly US government workers to the secretive Area 51 military base.

A fleet of passenger aircraft is stabled at Las Vegas McCarran International Airport to ferry workers to the off-limits area in rural Nevada, and anyone who boards one is sworn to secrecy about where they're going and what they do for a living.

The planes, which don't carry any company logos – they're plain white with a red band down the side - are operated by the US Air Force and are often referred to as Janet Airlines because that's the call sign the planes in it use while in civilian airspace.

One of the unmarked secretive aircraft that fly between Las Vegas and Area 51. The service is now advertising for a pilot

Now it appears that the airline is looking to hire a new first officer pilot after posting a job vacancy on the website of AECOM, a private defence contractor that operates the service.

According to the job description, the successful candidate will be expected to transport passengers and cargo and to ensure the safety of the flight at all times.

He or she will also be given the responsibility of ordering changes in fuel supply, load and route and must adhere to the procedures of the federal government.

The ad also states that all candidates must have a minimum of 3,000 fixed wing flying hours with 300 of them within the past five years.

The Area 51 base in the Nevada Test and Training Range, which is a secretive off-limits area owned by the US government

In addition to holding various different pilot licences, they should also be able to qualify for government security clearance and must be willing to live in the Las Vegas metropolitan area.

Earlier this year, an ad was placed on the AECOM wesbite for a member of cabin crew to work on the airline.

According to that vacancy ad, candidates were told they should be able to perform regular flight attendant duties such as passenger safety briefings, emergency procedures and light cleaning.

It is believed that all Janet Airlines flights fly out of a private terminal at McCarran nicknamed Gold Coast.

From Las Vegas they fly north-west to a place that has what's widely regarded as the most restricted airspace in the world, the Area 51 base in the Nevada Test and Training Range.

It has been reported that once the Janet aircraft approach this secretive area their call signs change from the likes of 'Janet 210' to 'bones 58'.

Services to Area 51 operate from a secretive terminal called Gold Coast at McCarran International Airport in Las Vegas, pictured

Nick Pope, author of Encounter in Rendlesham Forest and the man who used to investigate UFOs for the British Ministry of Defence, explained to MailOnline Travel that Area 51 is the place where some of America's most hi-tech military hardware is built and tested – but he doubts any of it is extra-terrestrial in origin.

He said: 'Area 51 exists - it's part of a military testing range in Nevada - and because of the remote and sparsely-populated location, it's where various secret prototype aircraft and drones are developed and test flown.

'The UFO and conspiracy theory community think it's the place where crashed UFOs are kept and where the US military are trying to back-engineer this alien technology.

'Sadly, despite the rumours, I've seen no evidence that we've recovered any extraterrestrial technology.'