Aeroplane behemoth Boeing has flown under the radar with the secret launch of its new 777X jet, the world’s longest passenger plane.

Boeing quietly unveiled the new aircraft to staff late last week without the usual media fanfare, amid the grounding of the manufacturer’s flagship 737 MAX 8 fleet following the deadly Ethiopian Airlines crash on March 10.

Boeing unveiled the new 777X to the employee today without media debut. Here are few photos of her from Boeing employees. Credit: Boeing Employee#777x #Boeing777X pic.twitter.com/z4L8Jkzrah

— Sam Chui (@SamChuiPhotos) March 13, 2019

Designed for fuel-efficient long-range flights, the 777X comes in two models, the 777-8, which seats 350-375 passengers, and 777-9, which seats 400-425 passengers.

At 77 metres, the new 777-9 model is the longest passenger plane ever built, 1.64 metres longer than Airbus’ A340.

Featuring “hi-tech” folding wingtips the 777X is a “superb aeroplane”, Swinburne University director of aviation Peter Bruce said.

The plane’s “highly efficient” dual-engines mean it can cover more kilometres with less carbon emissions, he said.

The technological advancements of Boeing’s 777X also signals the end of large four-engine long-haul planes, with Airbus announcing the end of its A380, and Boeing’s iconic 747 “just about gone”.

“The long-range twin engine is a thing of the times, and both manufactures are going that way,” Dr Bruce said.

Passengers will also enjoy a more comfortable flight thanks to reduced noise, lower atmospheric pressure in the cabin, which increases the “feeling of wellness” for travellers, and turbulence mitigation technology.

The plane’s also features larger windows, a wider cabin, new lighting and new architecture.

The 777-8 and 777-9 models are listed at US$360.5 million and US$388.7 million respectively, with first deliveries expected in 2020.

Boeing to ‘fully cooperate’ with safety audit

The aeroplane manufacturer has moved to allay safety concerns surrounding its 737 MAX 8 planes following the Ethiopian Airlines crash that saw all 157 on board perish, and October’s Lion Air crash that resulted in 189 deaths.

On March 18, Boeing president and chief executive Dennis Muilenburg said the airline had “an ongoing and relentless commitment to make safe airplanes even safer”.

“Soon we’ll release a software update and related pilot training for the 737 MAX that will address concerns discovered in the aftermath of the Lion Air Flight 610 accident,” Mr Muilenburg said.

On March 20, Boeing announced that it would “fully cooperate” in an audit by the US Department of Transportation.

Facing its biggest crisis in years following the two fatal crashes, Boeing has also brought in a new vice president of engineering while dedicating another top executive to the aircraft investigations.

The management reshuffle comes as Europe and Canada said they would seek their own guarantees over the safety of Boeing’s 737 MAX, further complicating plans to get the aircraft flying worldwide after they were grounded in the aftermath of the deadly crashes.

The shakeup showed how the world’s largest planemaker was freeing up engineering resources as it faces scrutiny during crash investigations while also maintaining production of its money-spinning 737 single-aisle aircrafts.

Lawmakers and safety experts are questioning how thoroughly regulators vetted the MAX model and how well pilots were trained on new features.

For now, global regulators have grounded the existing fleet of more than 300 MAX aircraft, and deliveries of nearly 5000 more – worth well over $US500 billion ($A705 billion) – are on hold.

-with AAP