The Boeing 777X UNVEILED: World's longest passenger plane at 252ft makes its debut at factory ceremony, less than a week after the Ethiopian Airlines crash that killed all 157 passengers on board (9 Pics)

The first fully assembled Boeing 777X - the world's longest passenger jetliner - has been unveiled.

The aircraft had expected to be presented with much fanfare in a ceremonial debut at the plane manufacturer's plant in Everett, near Seattle, on Wednesday.

But as a mark of respect for those who died in the Ethiopian Airlines 737 Max 8 crash, it was instead unveiled in a low-key event that was only attended by Boeing employees.

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Boeing employees gather around the first fully assembled 777X aircraft at the plane manufacturer's plant near Seattle. The jet was unveiled at a low key ceremony attended by Boeing staff only 

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The aircraft that was unveiled is a 777-9, the larger of two 777X models. The 777-9 variant is 77 meters (252ft) long. The current longest passenger jet is the 747-8, which is 76.3 meters (250ft 2in) long

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The 777-8 will be able to seat between 350 and 375 passengers and the 777-9 between 400 and 425, depending on the buyer's layout requirements

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This graphic shows the size difference between the new Boeing model and its predecessors

Pictures posted to Twitter show the huge jet, which has foldable wing tips, inside a hangar at the Boeing plant surrounded by hundreds of people.

In one image, uploaded by the account Dj's Aviation, Boeing staff can be seen snapping photos of it - and its enormous engines - on their phones.

Other pictures posted by aviation enthusiast Katie Bailey show the wheels and one of the engines up close. 

The aircraft that was unveiled is a 777-9, the larger of two 777X models. It is expected to make its maiden test flight later in the spring.

Boeing claims that the 777X will be the largest and most efficient twin engine jet in the world, with 12 per cent lower fuel consumption and 10 per cent lower operating costs than the competition.

The 777-9 variant is 77 meters (252ft) long. The current longest passenger jet is the 747-8, which is 76.3 meters (250ft 2in) long. 

As well as the folding wing-tips – the 235ft wings are the biggest Boeing has ever made, over 30ft longer than the current model's wingspan – it also has bigger windows and overhead bins compared to the current 777 and 'advanced LED lighting'.

The two versions of the 777X - the 777-8 and 777-9 - cost $360.5million and $388.7million respectively.

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Staff were eager to snap pictures of the huge plane. It will make its maiden test flight in the spring

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Boeing claims that the 777X will be the largest and most efficient twin engine jet in the world. The image on the left was taken at the ceremony by Katie Bailey and posted to Twitter. On the right is another of her pictures taken at the ceremony, which shows the jet's huge wheels

The 777-8 will be able to seat between 350 and 375 passengers and the 777-9 between 400 and 425, depending on the buyer's layout requirements. In comparison the current family of 777s offer capacities of between 300 and 370.

There is also an improvement with range. The 777X can fly for 16,110km (10,010 miles), compared to the 777's maximum range of 15,800km (9,817miles).

Deliveries to customers are expected to begin in 2020.

Carriers that have placed orders are British Airways, All Nippon Airways, Cathay Pacific, Emirates, Etihad Airways, Lufthansa, Qatar Airways and Singapore Airlines.

Last year, Boeing released a video and pictures of a 'static' 777X rolling off the production line at the Everett factory.

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Carriers that have placed orders for the 777X are British Airways, All Nippon Airways, Cathay Pacific, Emirates, Etihad Airways, Lufthansa, Qatar Airways and Singapore Airlines

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Last year, Boeing released a video and pictures of a 'static' 777X, pictured, rolling off the production line at the Everett factory. It was built for testing and is not destined for the skies 

However, as it was a static model, it wasn't destined for the skies, but instead built for a series of year-long tests.

The unveiling of the 777X comes at a troubling time for Boeing as its entire 737 Max 8 fleet has been grounded in the wake of the Ethiopian Airlines crash that claimed the lives of all 157 on board.

The Boeing 737 Max 8 aircraft en-route to Nairobi from Addis Ababa plunged to the ground just minutes after take off.

Data has shown that the movements from the flight were similar to those of a Lion Air service on a 737 Max 8 that crashed into the Java Sea off Indonesia in October, killing 189 people.

In a statement, president, CEO and chairman of the Boeing Company, Dennis Muilenburg, said of the grounding: 'We are supporting this proactive step out of an abundance of caution. Safety is a core value at Boeing for as long as we have been building airplanes; and it always will be.

'There is no greater priority for our company and our industry. We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again.'