What are the similarities and differences between an Airbus A350-900 and a Boeing 777-300ER?

Both are popular widebody fly-by-wire twinjet airliners. However the direct A350 competitor to the 777–300ER is the A350–1000, and so I’ll refer to it as required. The A350 is the more advanced airliner, having flown 19 years after the 777. With the A350, while an advanced jetliner, Airbus has taken a conservative approach to technologies available, so the aircraft does not push boundaries as far as the Boeing 787 does, instead being built with the systems technological environment set out by the A380.

The A350–1000 is the direct competitor to the 777–300ER. In fact, it’s the second Airbus competitor to this 777 model, after the A340–600. (© Airbus)

The 777–300ER on its maiden flight in February 2003. The model went on to becoming the most successful variant of the 777. (© Boeing)

This discussion focuses specifically on the current generation 777, and not the 777x, unless that aircraft is mentioned.

The main differences between the A350–900 and 777–300ER can be summarised as the A350 flies further, while the 777 carries more passengers and payload. The 777 is a larger aircraft and has more powerful engines.

The following will be a bit of an in-depth look at the two aircraft. It is a ridiculous waffle, be warned.

General Characteristics

The A350–900 is a 66.80 metre long jet with a 64.75 metre wingspan. It seats 315 passengers in a two class layout. The aircraft has a 5.96 metre wide fuselage, which is 6.09 metres tall — the A350 has a double bubble fuselage like the 737.

The A350–1000 is 73.79 metres long and seats 369 passengers in a two class arrangement.

The 777–300ER is a 73.86 metre long airliner, with a 64.80 metre wingspan. The aircraft has a perfectly circular fuselage with a 6.20 metre diameter. In a 3 class arrangement, the aircraft seats 370 passengers.

Bottomline, the 777 is a physically larger aircraft than the A350.

Flightdeck

Both airliners are fly-by-wire, and represent their respective manufacturer’s flightdeck philosophical approach to flight. Fly-by-wire implies that there’s envelop protection and a substantial level of automation and safety features and flight aids which reduce flight crew workloads.

To be sure, the non-fly-by-wire 747–400 also has a substantial level of automation, so automation is not exclusive to fly-by-wire aircraft.

On Airbus airplanes, when envelop protection is available on normal mode, the flight controls cannot be manipulated past the hard limits, whereas for the corresponding normal mode on the 777, you can exceed the soft limits. The 777 has envelop protection in its three primary flight control computers, and on its four actuator control electronics computers.

The 777 cockpit philosophy is such that the controls are linked, back-driven, and force feed, so it feels and reacts as a non-fly-by-wire aircraft.

The A350 fly-by-wire system architecture is an adaptation of the common Airbus fly-by-wire cockpit, leaning heavily on development work for the A380. The A320, first flown in the late 1980’s is the earliest example of the Airbus digital flightdeck.

The 777 is Boeing’s first digital fly-by-wire aircraft. It retains an impressive suite of technologies. Some of those technologies are additional flight controls laws to the aircraft’s standard bank of code for the purpose of enhancing safety and operational efficiency. Two such flight control laws are tail strike protection and thrust asymmetry compensation — the latter also available on the 787.

For the 777–300ER, which features the semi-levered main landing gear, tail strike protection enables additional payload or better takeoff performance at any takeoff weight, at any operating condition, so has tangible value for airlines.
The other flight control law — thrust asymmetry compensation — automatically positions the rudder to counter yaw in the event of an engine failure on takeoff, dramatically decreasing pilot workload at this critical stage of flight.

Both aircraft feature dedicated maintenance access terminals — a computer terminal behind the flightdeck seats used for maintenance functions. The computer has aircraft maintenance literature loaded in its hard drive.

The maintenance access terminal for the Airbus A350. Many of its functions can also be performed on the EFIS displays for the pilots.

Both aircraft future cursor control devices for selecting menus on the liquid crystal displays.

The A350 now includes touchscreens.

Bottomline, the A350 has a more advanced avionics suite than the 777. In terms of technology, the A350 is closest to the 787.

Electrical

The A350 features two identical variable frequency generators per engine, with static rectifiers in the aircraft’s avionics bay.

The 777 features a single integrated drive generator per engine, plus a single backup generator per engine. The backup generator is of the variable frequency type, with static rectifiers in the aircraft’s avionics bay.

Both aircraft feature ram air turbines.

Bottomline, the A350 has a more advanced electrical generation system, with substantially more output than the 777. In this department, the 787 is far ahead of either due to its electrical system architecture.

A composite image made from Boeing and Airbus graphics detailing the electrical generation systems for the 787, 777 and A350. I’ve added detail for the 777x to the 777.
On the 777, any of the engine generators is sufficient to power all systems on the aircraft. It’s not entirely clear to me whether the A350 (& 787) require all generators.

Hydraulic

The A350 (like the A380) dispenses with the blue (backup) systems in the classical Airbus green-blue-yellow (left to right) hydraulic system layout, settling on two fully independent systems, with the blue system’s functions taken up increased electrical scope and self—contained electro-hydrostatic actuators. The A350 operates a 5,000 psi hydraulic system.

The 787 has electrochemical actuators which require no hydraulic servicing.

Each of the two hydraulic systems on the A350 are powered by two engine driven pumps and one electrical motor hydraulic pumps. The ram air turbine will provide an additional hydraulic pressure source.

The 777 has three fully independent hydraulic systems. The left and right systems are driven by one engine driven pump each, with one electrical motor hydraulic pump each. The center system has two electrical motor hydraulic pumps, and two pneumatic driven hydraulic pumps. The center pneumatic pumps can be driven by bleed air from either engine or from the APU, while the electrical pumps can be driven by any of the four sources, including the RAT. The RAT provides an additional hydraulic pressure source. The 777 operates a 3,000 psi hydraulic system.

Hydraulic system schematic for the Boeing 777.[1]

Bottomline, both these aircraft have substantial hydraulic systems redundancy, but the A350 has a lighter system by weight.

Fuselage

The A350 and 777 fuselages are largely assembled in the same way: panels riveted together onto a metal skeleton. The difference is the A350’s fuselage panels are composite.

By contrast, the 787’s fuselage is made from rolling composite material around a mould, curing it in an autoclave, then cutting out the windows and doors.

Bottomline, the A350 has more advanced structure than the 777.

Cabin Pressurization & Environment — pax relevant

The A350 has a standard cabin pressurization of 8,000 ft, and an optional 6,000 ft cabin altitude pressurization afforded by its composite construction. The 777 only does 8,000 ft, while the 787 only does 6,000 ft. The lower the altitude, the better the comfort level. The A350 (& 787) also offer higher humidity levels in the cabin environment than the 777, so less dryness experienced than on the 777.

The 777 does have a roomier cabin and larger cabin windows than the A350 — only the 787 currently has larger windows. The forthcoming 777x will have larger cabin windows than the 777.

Cabin windows of the Boeing 777 and Airbus A350 in this Boeing marketing piece for the 777x.

The A350–1000 has eight passenger doors to the 777–300ER’s 10, so the 777 has a substantially higher exit limit, which translates to higher seat count.

Bottomline, the A350 should be a more comfortable ride.

Landing Gear

The A350–900 has eight main landing gear wheels, while the A350–1000 mirrors the 777 with twelve. The A350–1000 has a longer wheel base than the 777–300ER.

The 777 has the more complex and heavier main landing gear design. The aft axles of the 777’s main landing gear are steerable, while the 777–300ER features a large actuator to accomplish both its semi-levered gear function, and the bogie trim function.

The 777 consequently has a smaller ground turning circle, and the semi-levered main landing gear improves the aircraft’s takeoff field performance by adding more than a metre of effective main landing gear height, while the aircraft’s tail strike protection control laws manage the tail clearance at rotation. Boeing has turned the 777’s takeoff performance into a fine art, with predictable field length at any weight, under any weather and altitude condition.

Airbus may have offset some of that latter 777–300ER advantage with the longer wheel base of the A350—1000 (just over 1 metre longer than the 777–300ER), which should provide the required tail clearance on rotation but with higher angle of attack, a fulcrum play — all things equal, which of course, they’re not.