How does the new Airbus A350XWB compare to the Boeing 787 Dreamliner?

This is a very long answer, so bear with me for a while.

One of the biggest differences between the 787 Dreamliner and the A350 XWB is that the 787 is what is known as a MEA - a More Electric Aircraft. Let me explain.

In the olden days, the control surfaces on the wings (such as the flaps, slats, ailerons, elevators, rudder etc) were directly connected to the pilot’s yoke with cables and pulleys. The pilots had to use considerable physical force to steer their aircraft.

Somewhere along the line, someone decided to change this system to one involving hydraulics. The pilots didn’t actually operate the control surfaces manually. When they moved the yoke, electronics were used to interpret the movement and activate hydraulic actuators that did the actual moving. This was a sort of power-steering for planes.

But while hydraulics made flying much easier for pilots, it was also a ticking time bomb, which killed 111 people one July afternoon in 1989.

Planes have 3 hydraulic systems, of which one is in use at any time. It’s a triple-redundant system, which means even if two of the hydraulic systems fail, the third can still be used to safely continue flying. But at the core of all three systems are pipes which carry hydraulic fluid under pressure. And all three systems must physically be present at the control surfaces that they are supposed to move.

On July 19, 1989, United Airlines flight 232, a McDonnel Douglas DC-10 carrying 285 passengers and 11 crew from Denver Stapleton to Chicago O’Hare, had an uncontained engine failure on the number 2 engine. On the DC-10, which was a tri-jet, the number two engine was mounted on the base of the tailplane. When the engine’s fan disc exploded, shrapnel shot out and punctured the horizontal stabilizer (the elevator) and the rudder. As luck would have it, pipes belonging to all 3 hydraulic systems were punctured. Fluid leaked out. Because all 3 of the systems lost pressure, the planes was left with no way to move its control surfaces, and hence, no way to steer.

The pilots, who were an experienced and adventurous lot, used differential thrust - differing the amount of thrust being produced by each of the wing engines - to bring the plane around for a landing at Sioux City in Iowa, but the crash landing still killed 111 people.

As a result of this crash, planes with hydraulic systems (which is pretty much every plane flying today) have valves in their pipes which automatically close off if they discover a loss in fluid pressure, which can localize fluid losses to the area of puncture. On 4 November 2010, Quantas Flight 32, an Airbus A380 flying from Singapore Changi to Sydney Kingsford had another uncontained engine failure which punctured hydraulic lines on its left wing. Valves automatically closed and stopped fluid from the rest of the areas of the aircraft from leaking out.

But this isn’t the only problem with hydraulics. Hydraulic fluid has to be incompressible. So it’s dense, which means it’s heavy. They’re also petroleum based, which means they’re flammable (although modern synthetic hydraulic fluids have taken care of that issue). And to maintain pressure, compressors have to be used. These are not electric compressors but pneumatic ones, and they run off “bleed air” - air taken out from after the compressor stage in the engines. Air that could have been used to provide valuable thrust.

Incidentally, bleed air is also used to provide heated compressed air to run the aircraft’s air-conditioning system, so that when the TAT is -32 degrees Celsius outside, you’re still sitting in a comfortable 24 degrees Celsius inside. And bleed air is also used to spin up the engine before it can start. A small turbine in the tail of the aircraft (known as an APU - an Auxiliary Power Unit) is used to produce this compressed air.

The Dreamliner wanted to change all of that. They mainly wanted to have a bleed-less engine system, but that meant the aircraft would not have any pneumatic pressure systems available to them. So they’d have to make everything electrical.

The Dreamliner can fly with two engines - the Rolls-Royce Trent 1000, and the General Electric GEnx. Both of them are modular, all-electric bleedless engines with massive electric motor-generators inside of them. The APU on the Dreamliner produces only electrical power, no compressed air. It’s also flight-certified, i.e., it can be kept turned on in-flight for additional power. The total electrical power available in a Dreamliner is 1.45 Megawatts, which is five times as much as is available in a conventional airliner. It’s enough power to power two average American households for a month.

Like all aircrafts, the Dreamliner has a triple-redundant system to move its control surfaces. Unlike other aircraft, two of them are electric, using motors in the wings to move the control surfaces. The third is a hydraulic system, compartmentalized with valves, and pressure is maintained using electrical compressors. The air-conditioners use electrical heaters and electrical compressors. Electricity from the airport’s ground power supply, or the aircraft’s new massive Lithium-Ion battery banks is used to electrically spin up the engines before they can be started.

The fancy expensive looking “mood lighting” and the “Boeing Sky Interior” all use LED lighting, which means it’s actually much more energy efficient that conventional airliners.

The Dreamliner is also built from composite materials, which literally saves hundreds of tons of weight. With all the electricity available on board, the aircraft uses super-sophisticated avionics to make flying the aircraft easier for pilots. Indeed, one of the systems the aircraft has actively senses aircraft movement during turbulence and automatically steers the aircraft to minimize passenger discomfort. The electric compressors are able to maintain a higher level of air-pressure inside the cabin, so the effective altitude inside the aircraft is a good 2000-3000ft lower than in other aircraft. The Dreamliner has higher air-humidity than other aircraft, all for greater passenger comfort. And the windows in the Dreamliner don’t have shutters, but Twisted-Nematic LCD panels which darken or lighten to vary the amount of light being let in.

Even with so many gizmos on board, Boeing claims the Dreamliner’s engines have to produce about 35% less power than conventional airliners to maintain the same amount of performance. 35% is a HUGE amount of savings for airlines.

So why is the A350, which came after the 787, a conventional pneumatic-hydraulic aircraft?

The answer is twofold.

Firstly, while the 787 is an all-new design (it only shares a cockpit layout with the 777), the A350 is an evolution of the A330. It has an all-new fuselage, an all-new wing, an all-new undercarriage (wheels), and all-new engines (the Rolls-Royce Trent XWB, which is basically just a Trent 1000 from the 787, but with a bleed-air system), but the internal systems are all borrowed, from the A330 and the A380.

Secondly, and most importantly, the conventional system is more reliable.

The 787 is a giant leap into uncharted territory. This is the first time such a large MEA has been designed for passenger use. The electrical systems support everything inside the aircraft and are under a lot of pressure. Boeing developed Lithium-Ion batteries for the Dreamliner because they can store more energy. But they also have a proclivity for pyrotechnics, which led to all the 787s in the world being grounded for half a year until Boeing re-designed and fire-proofed their batteries. The A350 simply switched to older Nickel-Cadmium batteries.

I had the fortune of being on a Dreamliner on a short domestic flight from Delhi to Kolkata in India, on a flight in which just two days before I flew, the microwave oven in one of the galleys caught fire mid-flight.

Then we’ve had body panels falling off mid-flight, cracked windshields, cockpit blackouts, transponder failures, and even cracked engine fan blades. It’s a miracle the aircraft has survived so many incidents without a single hull-loss. The 787 is just not reliable.

And this is where the A350 hopes to succeed. Featuring technology that has been proven for decades, the A350 promises to be reliable. And while not as efficient as the 787, the aerodynamic improvements and other fine-tuning should make the A350 more efficient than the Boeing 777, which is the A350’s other competitor.

I believe the future belongs to MEA. While Airbus chose to stick with proven technology, Boeing took the audacious first step to developing MEA technology. Boeing hedged its bets on the Dreamliner, and it seems to be slowly paying off. Slowly, but surely, the issues with the Dreamliner are being ironed out. Boeing recently shipped its first 787-9, a longer version of the Dreamliner, which incorporates the “bugfixes” from the first Dreamliners. And Boeing is steadily working on the 777X programme, which will replace the guts of the proven 777 platform with MEA technology from the 787 programme. Boeing’s 747-8 already borrows a lot of technology from the 787.

I’m firmly of the belief that as MEA technology matures, Boeing will, with its technology, begin to take an unassailable lead in the commercial airliner market with their later generation MEA airliners.