EVERETT, United States: In a mammoth factory that a Boeing manager calls the largest "on the planet" by volume, the aviation company is assembling the world's biggest double-engined aircraft: the 777X.

The Seattle-area plant is filled with several of the flying behemoths at various stages of production, with the snow-capped mountains of Washington state peeking out from behind an open hangar door.

Boeing's Everett plant will be tasked with assembling three versions of the jet: the 777-200 cargo plane, which is based on a 777 model already in service; the next-generation 777-9 which is still being certified; and the 777-8, another new model that is slightly smaller than the 777-9.

The company has been under heavy scrutiny following a near-catastrophic January incident on a 737 MAX aircraft operated by Alaska Airlines, which saw a door plug blown out mid-flight.

Several other high-profile mishaps involving its aircraft - although none on 777s - have upped the pressure on the manufacturer, with the company announcing steps to enhance safety and quality control in response.

Company officials insist Boeing's long-term prospects remain bright, however, due in part to the new 777X.

The 777 - a stalwart of long-haul commercial aviation - is "the most successful twin aisle airplane of all times," Brad Till, a managing director at Boeing, told journalists during a factory tour held late last month.

Boeing has received more than 2,250 orders for 777 models since the plane family was launched 30 years ago, and 777s have flown roughly 3.9 billion passengers on 15.9 million flights.

Boeing unveiled the most recent incarnation of the jet, the 777X in 2013.

Deliveries were originally targeted for 2020, but the company hit obstacles during the certification process, with orders now expected to be fulfilled starting in 2025.

Boeing recently cleared a key regulatory hurdle on the 777-9, garnering Type Inspection Authorization (TIA) from the US Federal Aviation Administration.

"We began certification flight testing with FAA personnel on board the aircraft," Boeing said on July 13.

The designation represents a milestone in the aviation certification process and follows extensive agency review of technical data.

Boeing's announcement on TIA lent the embattled plane maker some momentum heading into next week's Farnborough air show in Britain, where the company will showcase the 777.

The company's display will highlight the 777X's more roomy cabin compared with its predecessor the 777-300 ER, thanks to a thinner fuselage.

Features include more spacious baggage compartments and a sophisticated LED lighting upgrade for longer flights that will mimic light at an aircraft's destination in a bid to counter jet lag, according to Till.

The jet's engines have fewer blades, reducing noise, while the aircraft's superior efficiency requires less fuel, Till said.

"The carbon dioxide emissions are 20 to 30 percent less" compared with the A350, the dual-aisle plane produced by rival Airbus, said Till.

"A large portion of the market for this aircraft is going to be replacement demand," he said.

Ted Grady, chief pilot for the 777/777X program, said the wing tips on the new plane can pivot in around 20 seconds, giving the jet added agility in spite of its enormity.

This feature effectively reduces the 72-meter wingspan by about six meters.

Grady is overseeing the flight testing program on four jets, which will be reviewed for propulsion and undergo analysis under various scenarios, including a flooded runway and strong crosswinds.

A test aircraft displayed during the media tour resembled a finished plane from the outside.

Its hollowed-out interior, however, contained just a few seats for engineers and mechanics, along with monitors, cameras and cables.

There were also a dozen black tanks filled with water, which were added to simulate the weight of a fully outfitted plane with seats, bins, kitchen carts and other equipment.

Grady was confident the aircraft can stand up to the rigors of the certification process, and of life in service.

"We have flown more than 3,500 hours," Grady said. "We have 40,000 cycles of fatigue testing, well over the span of the lifetime of the aircraft."

 - AFP