How are the Airbus A350 and A330 different?

Aha, as a little warm up to my A350 conversion soon let me use this opportunity to compare some systems of the A330 and the A350, before I have to delve into the manuals and will know too many technicalities to answer this concisely. I’ll be writing about the A350-900 as it is manufactured today, Anno Domini 2015.

1. General

(The difference in dimensions between an A330-200 and an A350-900. The 350 is a bit bigger. That was obvious and you didn’t need me for that, duh.)

(The cabin is wider, longer and there’s more space for cargo. Also duh.)

the maximum takeoff weight, max landing weight, max zero fuel weight and max fuel load in ton are (with a bit of margin for error on the fuel weight):

• for a latest version of the A330-300: 235, 187, 175 and 76 respectively
• for an A330-200: 238, 182, 168 and 111 respectively
• for the A350-900: 275, 207, 195 and 111 respectively.

 

(That extra capacity allows the A350 (on the right) to carry more payload further and that for less fuel per kg transported. - Together with the cargo, you, the passenger, are the payload, unless you got a free ride from the airline of course, in which case I’d have to inform you that someone has to pay our salaries so you better don’t do that too often. )

The A330 flies maximum speeds of 330 kt indicated and M.86.
The A350 flies maximum speeds of 340 kt indicated and M.89, a bit faster. Therefore 350 pilots will be often annoyed by slower traffic ahead, stealing precious time from them; time that they can otherwise spend drinking wine in Italy, eating sauerkraut in Gemany, chewing off lamb chops in New Zealand or barbecuing slivers of steak in South-Korea.

The cockpit looks different of course, with some extra screens for fancy stuff in the A350. The A350 also has a HUD (head up display). There’s a special terminal with screen and seat for maintenance in the back of the cockpit so the engineers can electronically sign off the airplane and take care of aircraft issues without disturbing the pilots.

(New screens and displays, extra real estate to look at numbers, digital dials, messages, love notes from the plane. I’m sure I’ll love you back, sweet lady.)

There’s also a flight crew rest area above and between the front passenger doors in the A350 where pilots can snore away their waking worries or watch which main character gets eliminated the latest episode of Game of Thrones on the inflight entertainment. That will become my favorite spot in the plane, I can feel it already. But only during flights where inflight rest is required to extend the duty of course, and where one or two extra pilots are taking care of our passengers, that goes without saying.

(Check out the neat flight crew rest area behind the cockpit and above the front doors where you, dear passenger, unknowingly if you hadn’t read this, will board the airplane through. I can’t wait to try those beds while watching Star Wars VII, let’s say on a flight to Paris or Madrid. Of course my colleagues in the front will continue to fly the plane for you while this scene takes place.)

2. Systems related to air

There’s an inert gas system in the A350 for the fuel tanks. It pressurizes the fuel with non combustible nitrogen enriched air. Makes me think why on earth every single other airplane never exploded up there (except the unfortunate TWA800 747 of course). Should I feel unsafe now in other planes?

Temperature regulation for the cabin is better organized and better optimized in the A350, with 7 different cabin zones, and - life gets easier for the cockpit crew - the cabin crew sets the temperature. On the 330 the cockpit crew sets the temperature and the cabin crew has a 2.5 degrees Celsius margin on both sides of that setting, resulting in them every now and then asking us to “warm up the cabin a smudge” or requesting “can you cool it down a scintilla cause we’re sweating our makeup off?”.

Cabin pressure will be maximum 7,800 feet for long flights and 6,000 feet for short flights on the 350. On the 330-300 that’s 7,460 feet for long flights and 8,000 for short flights. I don’t know why Airbus decided on those values; maybe someday someone somewhere somehow will tell me. Launch the question on this platform if you can’t wait.

There are some different valves and computers to make that pressurization and air conditioning happen.

The avionics ventilation is also arranged a bit differently, with on the 350 extra cooling possibility for those hot avionics and extra ventilation possibility in case of smoke in the avionics bay, our so called “basement” below the cockpit.

3. The autoflight system

Flight envelope and flight guidance computing is done by the PRIM flight computers of the A350, not by the FMGCs like on the A330. I realize this is getting too technical here so I’ll take some gas back, don’t worry. Apologies.

An A350 has 2 KCCUs (Keyboard and cursor control units) to interact with the FMS (flight management system, a bit the brains of the autoflight system if you will), effectively giving the airplane a computer mouse with QWERTY keyboard. The next step will be Quora access for if there’s a problem and we have to ask Tim Hibbetts or John Chesire what to do. Some more display real estate with fancy modern gadgets like a mailbox to interact with air traffic control and the company are present. There’s also a keyboard built into the widely beloved Airbus-table, ever ready in front of the pilots to receive a leftover meal from first class.

Some new autopilot modes and possibilities are introduced on the A350. Losing the autopilot in case of failures is less likely. Possible pilot errors like lining up on a wrong runway are caught by the system and the pilots get warnings for those.

(The way to interact with the flight management systems is taken up a degree. Some new fancy possibilities in flight management are helping the pilot out more as well. Quora collapsed one of my previous answers to a question because it contained text in pictures, so please don’t report me for this one here. Ignore the text on it if you can’t stand it or better yet, don’t read on. Ciao.)

The autoflight computer architecture of the A350 is different, there’s some more redundancy.

4. The electrical and hydraulic systems

Every engine has two generators on the A350, while the A330 only has one per engine. The AC Voltage is pumped up a bit to 230 V, with converters bringing that to the familiar 115 Volt for some electrical busses and consumers connected to them. The whole electrical network seems a bit more complicated to me, with more busses, more transformers, more batteries… and it was never my favorite system to learn to start with, bugger.

The higher voltage and power allows flight controls to be controlled with electric actuators as a backup, instead of relying on hydraulics only.

There are only two hydraulic systems, called Yellow and Green on the A350. The A330 still needs a third system: the Blue system.

Newbies on the Airbus are often pointed out that the hydraulic fluid is not really that color so they shouldn’t look for blue fluid if they suspect a leak in the Blue system, haha. Of course there are still two hydraulic pumps per engine, one pump for each system. The A330 has a Green pump (not really painted green of course, haha) on each engine and then a Blue pump (haha, same joke) on one engine and a Yellow pump (no more, please no more) on the other. The electric hydraulic pumps that act as backup are more powerful on the A350 as well.

The A330 has a 3,000 PSI hydraulic system. I wonder if that’s the reason for the name of the type: the 350 has a 5,000 PSI system. If a future A360 will have a 6,000 PSI pressure we’ll know we’re onto something.

5. The flight control system

The electric actuators from independent power sources provides the extra redundancy on the newcomer.

More spoilers, more slats on the A350 too. If you think Airbus called the inboard slats still slats on a 350, you’d be wrong. They are called DNDs. For the common folks and for airline crew sleeping in hotel rooms those letters imply that they don’t want to be disturbed but for the A350 people that means Droop Nose Devices.

There’s a third PRIM (there he is again with his PRIM) installed on the A350. A PRIM is a primary flight computer that sort of checks if the pilot is not too stupid in his demands on the airplane. It takes care of the fly by wire sorcery and helps out when there’s a windshear or when there’s a need to go full backstick to get away from the unforgiving surface of the earth if landing is not going to be the likely outcome of the manoeuver at hand.

(The flight control architecture of the A350. P1, P2 and P3 stand for the beloved PRIM computers. S1, S2 and S3 stand for the three - I’ve found an excuse to say it - SEX… ok, SECS with a C and an S then, of course meaning Secondary flight computers. A lot of redundancy. Moreover, the A350 doesn’t need hydraulics anymore and can fly on electrics only. Leak away now if you dare, naughty Yellow and Green systems.)

Inner and outer flaps can move independently from each other, enabling a differential flap setting to improve handling at low speeds. Fancier than that, during cruise the flaps are used to shape the wing to optimize the ride, minimize the drag and manage the center of lift. This fancy feat of engineering renders the trim tank, a fuel tank in the tail to control the center of gravity, useless. Therefore A350s have no fuel tank in the tail like A330s do, insinuating that I lied here: Bruno Gilissen’s answer to Where is fuel in a passenger aircraft stored and what is the typical capacity?.

6. the fuel system

The center tank of the A350 extends into the root of the wings. The center tank pumps are the more powerful brothers of the wing tank pumps and so fuel from there is forced to the engine more assertively. There are two crossfeed valves to connect left and right too, again a bit more redundant than on the A330 with only one such valve.

No trim tank on the 350, as mentioned above.

(The fuel tanks of the two sexy sisters: an oversized center tank in the A350 and no trim tank. Stability and fuel optimization is achieved by moving the center of gravity on the A330 where fuel can be pumped to the tail; it’s done by moving the flaps on the wing in cruise to shift the center of lift on the A350. Neat.)

7. the Navigational systems

The weather radar and the ground proximity warning system have a vertical profile shown on the navigation display on the A350, allowing a pilot to see how tall that cumulonimbus is and how exactly the mountain in front of him rises.

The probes responsible for measuring altitude, airspeed, angle of attack and total air temperature of the A330 are all integrated in the new Multifuction Probes. There are also sideslip angle probes on the A350, not on the A330. There’s a 4th probe ensemble - an old style pitot and static - on the A350 for the standby instruments. On the 330 three probe systems were enough.

Awareness is increased by a slicker Terrain Awareness System on the 350. Traffic Collision and Avoidance System (TCAS) on the newbie directs the autopilot and the pilot doesn’t have to manually intervene anymore. ATC is automatically notified in that case.

There’s also an Airport Navigation Function with a moving airport map on the navigation display. This will soon also display other traffic at the airport. If a controller clears the A350 via text message (called less fortunate CPDLC in aviation lingo) the cleared route is displayed. There’s also a cross check by this system to see if the pilots are on the correct runway for takeoff and at the right intersection. A warning for if those idiots are approaching the wrong runway should prevent nasty runway incursions. Finally, if they want to kiss it down too smooth and use up half the runway to float in that effort, the A350 will warn them when not enough pavement is left to guarantee that they make it before ending up in the herd of spotters taking pictures at the opposite end.

8. Avionics

(A different concept of gathering data and connecting computers and avionics chips on the A350, allowing each instrument access to any information from any system.)

The whole concept of connecting avionics is different on the A350. Conventional avionics is available as backup but otherwise there are series of Ethernet switches that make the whole architecture more akin to the internet than to copper wires from System 1 of something to the Captain, System 2 to the FO and system 3 as standby to both.

9. A new era in flight documentation

The A350 has an Onboard Information System (OIS). That contains what in the days of yore was carried in books and folders and nowadays in a lot of airlines on ipads, plus more: performance calculation, charts, maps, manuals, logbook, operational documents. The airline’s operational control can piggyback on all the info to streamline the operations and minimize the delays for you, dear valuable passenger.

(The only paper left in the cockpit will be the napkins that come with the tomato juice topped with black pepper and tabasco.)

10. Engines and APU

The APU (Auxiliary power unit, that noisy little jet engine in the tail that the neighbors of the airport wish was never invented) is a bit more powerful, having to supply a more potent electrical system.

The A330 flies with Rolls Royce’s Trend 700 series engines (or General Electric’s CF6 series or Pratt & Whitney’s PW4000 series) rated at 72,000 pounds of thrust.
The A350 has two Rolls Royce Trend XWBs strapped on that are currently rated at 84,000 pounds thrust. Their reverses are not hydraulically - as on the 330 - but electrically operated.

Cool and something I’ve always wondered about as to why it was never so before (Jet Engines: Why is the maximum RPM for engines and APU more than 100 percent on aircraft types?), on the A350, 100 percent RPM is the maximum the pilot can get. Period. No silly “under these conditions it’s only 93.2 percent” and “the absolute max N1 is 103 percent while the max N2 is 99 percent”. 100 percent is 100 percent, basta. - “Crikey, Jimmy, I wonder how much RPM we can maximum get out of our power plants right now?” - “Why, 100 percent Nigel, of course.”

11. Some other trivia differences

On the A350, a system allows wireless communications with the company on the ground. The radio control panels are fancier.

An overheat detection system is installed in the main landing gear bay, enabling fire detection there.

The DFDR data is easier accessible so the airline can check better if their pilots are behaving and flying the way they want. Wireless transmission of that on the ground is optional. Holy guacamole, they can soon call us on our mobile instantly if we taxi too fast if this trend goes on.

There are different computers and a new design behind the displays and the way instruments are presented.

There’s a function called “Brake to vacate” on the A350, which allows the pilots to choose which taxiway they want to use to roll off the runway after landing. Automatic braking is adjusted to make it happen.

There are 3 Radio Altimeters on the A350, only 2 on the A330.

The bulk cargo door in the back is on the left side of the airplane on the A350. On the A330 it’s on the right side with the other two cargo doors.

An escape hatch is located in the cockpit to enable an evacuation if the door is blocked. In the A330 the pilots use their sliding windows for that.

There, now let me open the FCOM (Flight Crew Operations Manual), electronically only for the A350 of course, to see for myself how much I still have to learn.