The Year for Boeing’s Big Twin?

Delays are blighting introduction of the Boeing 777X but with its record-breaking capacity and revolutionary wing design it holds great promise. Mark Broadbent considers what can be expected when the twinjet finally flies.

An earlier CGI of the Boeing 777-9, which with 414 seats will be the largest-capacity twinjet airliner ever produced.

Boeing’s pre-eminent 777 remains ‘big twin’ the in the commercial airliner market – nearly 25 years after entering commercial service with United Airlines in May 1995. In this time, more than 1,500 examples have been sold, with major network airlines using the type to serve high-density routes between hub airports. The milestone of a quarter-century of Triple Seven operations will be reached as Boeing works on the latest-generation 777X.

First Flight Pushed Back

The 777X programme was launched in 2013 with two variants, the 777-9 and 777-8. It was always planned to develop the 777-9 variant first, with the first target to deliver the examples to early operators in 2020.

The initial flight-test aircraft, N779XW (c/n 64240), rolled out of Boeing’s Everett factory in March 2019 and undertook ground tests and taxiing trials that summer. However, flight-testing for this and the second example N779XX, c/n 64241) will only begin in early 2020.

The holdup has been caused by an issue with the General Electric GE9X turbofans that will power both 777X variants. At the Paris Air Show in June 2019, GE revealed an undisclosed problem had been found in the stator vane in the second stage of the powerplant’s high-pressure compressor during reliability trials. This led to a redesign on the GE9Xs already delivered to Everett for the two flight-test aircraft.

Separate to the GE9X issue, during the final loads assessment on the 777-9 static airframe in September 2019 which involved bending the wings upwards to a level far beyond anything expected in commercial service, “an issue arose that required the team to suspend testing”, according to a Boeing statement.

Boeing said the “issue” involved “a depressurisation of the aft fuselage” in the final minutes of the trial when loads were at about 99%. A Seattle Times report claimed a cargo door had failed.

The static aircraft has been successfully undergoing evaluation since June 2019, according to Boeing. It said: “While our root cause assessment continues, at this time we do not expect this will have a significant impact on aircraft design or on our overall test programme schedule. We remain fully focused on safety as our highest priority, as we subject the 777X to a rigorous programme prior to first flight.”

For several months, Boeing publicly stuck to the initial target of delivering the first customer 777-9s in 2020. However, with flight testing postponed until early next year and considering it typically takes 12-18 months to certificate a new airliner, a later-than-planned introduction appeared inevitable. Boeing confirmed in its third-quarter results issued in mid-October 2019 that it “is now targeting early 2021 for first delivery of the 777X”.

The first two 777-9s for launch operator Emirates and the initial aircraft for fellow early operator Lufthansa are on the Everett production line. With 126 aircraft, Emirates has ordered more 777Xs than any other customer by some margin.

Largest Twinjet Airliner

The 777X is the largest twinjet passenger airliner ever developed. At 251ft 9in (76.72m) in length, the 777-9 is 7ft (2.1m) longer than the 777-300ER compared with the 250ft 2in (76.2m) 747-8, the latest jumbo, and the 72.7m (238ft 7in) A380.

According to Boeing’s ‘Aircraft Characteristics for Airport Planning’ document, the variant will have 414 seats in a standard two-class, ten-abreast 3-4-3 layout, up from the 777-300ER’s 396 seats two-class configuration. It will have a range of 7,525nm (13,936km).

The extra capacity has been achieved by widening the cabin by 2in (50mm) on either side of the fuselage with scalloped frames. The 777-9’s greater length also means it will be able to carry 46 LD-3s (26 in the forward hold and 20 in the rear hold), up from 44 LD-3s on the 777-300ER.

The 777-9’s capacity and range is an increase from the 777-300ER’s 396 seats and 7,370nm (13,650km). Boeing claims the 777X will be 20% more fuel-ef icient per seat than its predecessor.

Boeing rolled out the initial flight-test 777-9, N779XW (c/n 64240), in March 2019.

Engines and Folding Wings

Although the 777X looks like the current-generation Triple Seven, two key dif erences between the aircraft and the earlier models are readily apparent from a cursory look at early photos of the 777-9 undergoing ground taxiing trials at Everett: the GE9X engines and folding wing tips.

The GE9X has the largest fan diameter of any commercial jet powerplant ever developed at 34in (863mm) – astonishingly it is wide enough to accommodate the fuselage width of a Boeing 737 – and will generate 105,000lb (470kN) maximum take-off thrust.

The folding wing tips stem from Boeing’s desire to have a wide wingspan for the 777X as per the company’s overall approach to widebody aircraft design, which is to maximise aspect ratio and improve lift-to-drag characteristics, while maintaining taxiway and gate compatibility.

International Civil Aviation Organization (ICAO) regulations on safety separations between aircraft and ground objects at airports mean jets with wingspans of 107ft 6in to 213ft 2in (52-65m) are classified as Code E and aircraft with wingspans of 213ft 2in to 262ft 4in (65-80m) are in a separate category, Code F.

The full 235ft 5in span of the 777X in flight would make the aircraft Code F rather than Code E, where the current production models sit with their 212ft 9in (64.8m) dimensions. The new variants would therefore be unable to use the same gates and airports would potentially be required to make infrastructure changes to accept 777Xs.

Boeing’s solution was to design 7ft-long (2.1m) folding wing tips, a mechanism never used on a commercial airliner before. At the gate, with these outboard sections in an upright position, the 777X will have the same 212ft 9in (64.8m) span as the current 777s.

When the 777X is approaching the end of the runway prior to departure, the crew will use a control panel on the flight deck to activate a folding wing tip mechanism (FWT) to lower these outboard sections, extending the wing to its full span for flight. When the 777X has arrived at its destination, the FWT mechanism will automatically retract the wing tips after the aircraft has touched down and the ground speed is below 50kts (92km/h).


Composite Wing

Carbon fibre reinforced plastic (CFRP) composites are used in many new aircraft to eliminate the typical features of a traditional metallic structure, such as fasteners, joints and overlaps, and therefore save weight and boost performance.

The 777X is no exception. The entire wing spar, its panels, skins, stringers, ribs, tips and leading and trailing edges are all made from carbon fibre. At 105ft (32m) long, the 777X wing spar is the largest single-piece composite part ever developed for an airliner.

A purpose-built Composite Wing Center (CWC) at Everett manufactures four CFRP spars and four panels for each 777X, and a Boeing Fabrication facility in St Louis, Missouri supplies the CFRP leading and trailing edges, ribs and folding tips.

The composite wing and its folding tips are not the only airframe differences between the 777X and earlier models. The new-generation jets have completely redesigned fuselage fairings, a new wing-to-fuselage fairing and a new empennage. They will also have a variable-camber trailing edge to adapt the wing position and a gust suppression system that will automatically adjust the flight controls to distribute the wind evenly across the wing.

It recently emerged that Boeing is reducing the amount of automation used to produce the new 777. Building on its experience producing the 787 Dreamliner, for the 777X the manufacturer introduced a process called fuselage automated upright build (FAUB), with robots working in tandem to drill holes precisely and fasten together metal panels held upright.

However, a Bloomberg report in November said problems keeping the robots moving in sync created production holdups. The report maintained the manufacturer has dropped the FAUB concept and is instead using a partially automated process, with mechanics manually inserting fasteners into the robot-drilled holes. A changeover to this process began during the second quarter of 2019 and should be complete by year’s end, the report added.

The two Boeing 777-9 flight test aircraft, N779XW (c/n 64240) and N779XX (c/n 64241) at Boeing’s Everett factory in October 2019. Ding
Fresh angle: the 777X’s 7ft-long (2.1m) folding wing tips, a mechanism never used on a commercial airliner before.

What Future for the 777-8?

The 777-8, the second 777X variant to be developed, will be 23ft (7m) shorter than the 777-9, consequently it will have lower capacity than its sister aircraft (365 passengers in a two-class layout).

However, the 777-8 is optimised for range and undertaking hot and high altitude, long-range/hot and long-range/high payload operations. The variant will have 8,690nm (16,090km) range, considerably further than the 777-9’s 7,525nm (13,490km) capability.

Boeing always planned to introduce the 777-8 around 18 months after the 777-9’s service debut, but the delays to the baseline variant’s development prompted the company to press the pause button. A Boeing spokesperson told AIR International: “The adjustment reduces risk in our development programme, ensuring a more seamless transition to the 777-8.”

British Airways became the first airline to place an order for the 777X for nearly two years in February 2019, with an initial 18 examples.

The delay raises a question about exactly when the 777-8 will emerge given the relatively few orders for the variant. Of the 777X family’s 325 orders, as of October 2019 only 45 were for the 777-8, comprising 35 for Emirates and ten for Qatar Airways.

However, perhaps a smallish number of orders for an aircraft with the 777-8’s configuration isn’t so surprising. Although the range maps for the 777-8 on Boeing’s website show the variant will be capable of flying ultra long-haul city pairs such as London Heathrow-Perth and New York JFK-Auckland non-stop, assuming a 365-passenger, two-class layout, ultimately there are only so many airlines that need such a capability.

The Boeing Business Jets version of the 777X was launched in December 2018, with the BBJ 777-9 of ering a 3,689sq ft (342.7m2) cabin.

Comparing the Big Twins

The 777X’s head-to-head competitor is the Airbus A350-1000. The 777-9 is larger than the A350-1000, with a longer and wider fuselage and a wider wingspan and higher take-of thrust.

Despite the extensive use of carbon fibre in its huge wing, the 777X still has traditional materials, with aluminium used for the fuselage and central wingbox. The A350-1000 contains a comparatively higher share of CFRP and other advanced materials.

There is a more than 77,000lb (35,000kg) dif erence in ramp weight between the 777X and A350-1000 and Airbus claims the wings, folding devices and engines mean the 777X’s total maintenance cost will be 37% higher than the A350’s. Boeing, of course, disagrees, and says the 777X will be up to 10% cheaper to operate than an A350-1000, will generate up to 12% less carbon dioxide emissions and be 20% more fuel-ef icient than its European competitor.

According to an analysis by Leeham News and Insight, long-established analysts of the commercial aviation industry, the 777X and A350 are closely matched. In a report published in 2018, it claimed that although the A350-1000 of ers a superior operating empty weight, the 777-9 has a 3% lower costper-seat-mile which, it says, “is valid for long flights” and that it “is a question of the capacity needs of the airline on its route structure” as to whether a carrier picks a 777X or an A350.

As the CAPA Centre for Aviation consultancy has pointed out, each individual airline has dif erent capacity, payload and range requirements, which inevitably means some carriers will pick one design over another.

The nature of aircraft purchasing, however, means in practice many network airlines end up selecting rival aircraft to fulfil slightly dif erent missions in their fleet, with one aircraft regarded as more suitable for certain markets and another type more suitable for others (for example, both British Airways and Qatar Airways have ordered 777Xs and A350-1000s). Buying examples of rival families provides the flexibility on payload, range, seating and cargo that large airlines like to have.


Big Twin Market Dynamics

The 777X has not sold quickly, with the 325 orders spread over the seven years since its launch. A February 2019 order from the International Airlines Group for up to 36 777-9s for British Airways was the first new order in nearly two years.

The 777X’s sales record is part of a wider slowdown in sales of large widebody airliners (those of the A350-1000 are thin too, with just 180 sold by October 2019), although orders for smaller widebodies such as A330s, A350-900s and 787s continue to tick along. Why is this the case?

One factor is airlines have arguably already ordered what they need. With production slots filled well into the 2020s, availability is pushed back, which possibly limits interest in them.

Linked to this, many carriers have already introduced equipment for these requirements relatively recently, which further pushes out demand. As a CAPA analysis has noted, although the 777-300ER was first introduced to service back in 2004, half of all 777-300ERs have been built since 2012, which means replacing these aircraft – and older ones which still have life left in them – lies many years ahead.

Another issue influencing widebody sales is the increasingly fragmented nature of the market. Recent years have seen a reduced appetite for the largest widebody aircraft. No longer do the biggest airliners hold the monopoly on flying lots of people over long distances. Widebodies such as A330s and 787s of er high levels of ef iciency and performance although they are smaller in size, while the improved payload/range capabilities of ef icient single-aisle jets, exemplified by the A321XLR (which has 4,700nm/8,400km range), has introduced a further dynamic.

However, the most important factor influencing demand for an aircraft of the 777X’s configuration is that only a small number of major airlines have suf iciently large networks and passenger/cargo flows to sustain aircraft of that size.

This doesn’t mean there will be a lack of demand for aircraft of the 777X’s size. There is a role for a large, high-capacity and long-range aircraft; it’s just that the market’s dynamics might mean airlines buy these types more selectively.

The 777-8 variant has a shorter-fuselage but a longer-range

Boeing Business Jet 777X

Separate to the main 777X versions, in December 2018 Boeing launched the BBJ (Boeing Business Jet 777X), a new model that Boeing said “can fly more than half-way around the world without stopping, farther than any business jet ever built”.

Greg Laxton, head of Boeing Business Jets, said: “Our most exclusive customers want to travel with the best space and comfort and fly directly to their destination. The new BBJ 777X will be able to do this like no other airplane before it, redefining ultra long-range VIP travel.”

Customers can choose between two models: the BBJ 777-8 and BBJ 777-9. The former of ers the longest range of 11,645nm (21,570km) and a spacious 3,256 sq ft (302.5m2) cabin. The BBJ 777-9 provides an even larger cabin measuring 3,689 sq ft (342.7m2), while still achieving ultra long-range of 11,000nm (20,370km). This model is designed to of er what Boeing called “almost unlimited interior design options to ensure ultimate comfort for long-distance travel”.

Whether it is as a business jet of ering luxury or an airliner flying between hub airports, the latest edition of Boeing’s big twin will make a big impression.

777X Timeline


November 2013

The 777X is formally launched at the Dubai Airshow, attracting 259 orders and commitments worth $95bn at list prices. First flight scheduled for 2019 and service entry for 2020.


August 2015

Basic design finalised following wind tunnel tests to help develop configuration. Detailed design work begins.


May 2016

Composite Wing Centre opens, introducing advanced robotic drilling systems.



Assembly of the first 777-9 test aircraft under way. Fuselage sections for early customer jets joined and static tests start.


March 13, 2019

The first 777-9 flight test aircraft rolls out. Boeing continues to target a 2019 first flight.

img_80_1.jpg Bhakta

June 2019

Flight test aircraft undertakes taxi trials.

GE Aviation
GE Aviation

July 2019

GE9X engine redesign pushes out first flight to early 2020.


September 2019

Depressurisation in the aft fuselage stops static ultimate load test.


October 2019

Boeing confirms service entry delayed to early 2021.


November 2019

Boeing reportedly abandons automated upright build process to construct wings. Launch customer Emirates scales back order.

Sir Tim: 777X Must "Go Through Hell on Earth"

Sir Tim Clark, president of the 777X launch customer Emirates, did not mince his words when he spoke recently of the aircraft’s ongoing development delays and the impact on the carrier’s fleet plans: “I want one aircraft to go through hell on Earth basically to make sure it all works,” he told reporters at the Dubai Airshow in the autumn amid media reports that Emirates is likely to receive an aircraft to test in the summer. It was also announced during the show that the airline has cut its order for the type from 150 to 126 aircraft.

His comments echo concerns among some industry executives about the development holdups and reliability snags af ecting many new airliner types introduced to service in recent years – from the 787 to the A320neo. Emirates was due to receive its first aircraft in mid-2020. However, there has been a lengthy delay to the start of flight testing. The first 777X delivery is now not expected until early 2021.

The 777X will be the first Boeing jet to be tested and certified since the two 737 MAX disasters in which a total of 346 people died. The Joint Authorities Technical Review, a panel of international regulators convened to appraise the US Federal Aviation Administration (FAA) certification of the 737 MAX, recently criticised the FAA’s review process. FAA Administrator Steve Dickson said in November the agency is considering how to alter the certification process for new aircraft in the wake of Congressional committees questioning the relationship between the regulator and Boeing.

Exactly how this influences the nature and length of the 777X certification process is yet to play out, but Reuters reported Clark as saying: “We need to be absolutely sure that as she comes together... everything is done in a manner that it should be done.” Meanwhile Boeing has previously stated: “We remain fully focused on safety as our highest priority, as we subject the 777X to a rigorous test programme prior to first flight.”