View Full Version : Main differences between Airbus and Boeing


A333
13th Nov 2004, 10:53
Hello,

I am not starting this thread for a B vs A war, if it's inappropriate please delete it.

However, I was just wondering what the main differences between the Boeing and Airbus. I know that Airbus has autotrim but don't really understand what that means. I also know that in the Boeing, it's harder to pull the yoke than the Airbus but don't really understand why.

Can someone please explain to me the key differences between an Airbus and Boeing? I've only flown a TIF so I don't really understand the expert version of the explanation. Would appreciate it anyone can explain it in simple form if possible. Thanks for your time.

A333



Spearing Britney
13th Nov 2004, 17:21
Well having only ever flown the electric wonderjet and not knowing what a TIF is I may not be the best to reply but here goes...

Modern Airbus aircraft (320/330/340) have a sidestick, like a computer joystick, not a yoke and have hard protections via the fly by wire system. This means you cannot stall it, overstress the airframe etc. They also allow you to cross-crew on more than one type, e.g. 320 and 340 flying one then the other day in day out.

Boeings (737/747/747/767) have conventional hydraulic controls, not fly by wire and all of them (777 included, which is fly by wire) have a conventional yoke. In the Airbus the controls (both stick and throttle) have no feedback or feel but in the Boeings they do (777 has synthetic feel). Boeings can be stalled, flown beyond airframe limits etc if the pilot ignores warnings and really want to.

Well thats a start, let battle commence...

ferrydude
13th Nov 2004, 19:14
Boeings can be stalled, flown beyond airframe limits etc if the pilot ignores warnings and really want to.

Hmmm, does this imply that Airbus aircraft cannot be stalled or flown beyond airframe limits?

Ka8 Flyer
13th Nov 2004, 19:24
"Hmmm, does this imply that Airbus aircraft cannot be stalled or flown beyond airframe limits?"

Yes! As long as the flight computers don't revert back into their "safe" modes, you are limited to:

2.5 G's
66° bank angle
Specific nose up/down attitudes.

Also, shortly before stalling, the aircraft's autothrust system will select max thrust and the attitude will be limited to a non-stalling attitude.
If you pull harder, nothing happens.

The same thing (well actually the opposite) happens if you are close to Vmo.
The nose will go up and the power will be limiited.

These safe guards are all turned off in the backup mode known as "Direct Law". There the stick functions the same as the yoke on other a/c.
You also have a mode between "Normal law" and "Direct law" which is called "alternate law" and there you still have some features (like autotrim) and safe guards.

Regards,

Mark

The African Dude
13th Nov 2004, 19:26
Nope.... this does!

Modern Airbus aircraft (320/330/340) have a sidestick, like a computer joystick, not a yoke and have hard protections via the fly by wire system. This means you cannot stall it, overstress the airframe etc.


Edit: K8Flyer you beat me to it!

oldebloke
13th Nov 2004, 22:06
The Main difference between Boeing and Airbus is that Airbus ia 'cheaper'...Not built to Boeing strengths(lighter) for more performance...But as a friend who has recently 'checked' out on the 757 said compared to the 320/330"it's a nice simple aircraft"(circ1980)
When I was asked how I liked the 320,after flying the 727 for 10 years,I could only reply"the 727 was stronger,I don't think the 320 will'last'as long as a 727...But any aircraft that can give me a single engine autoland in WOXOF conditions is'nt all bad"
Cheers:ok:

bantios
14th Nov 2004, 04:16
Just a few things i would like to clarify..

You can do anything u want on an airbus FBW system. Its as simple as turning off the flight augmentation computers and put the roll into alternate law. From there you can actually roll an airbus.

Airbus aircraft do have artificial feel in the side stick. The very firtst A320's did not have this but all other airbus's do. Having flown various aircraft, I still prefer the old fashioned yoke on the boeing. It makes it much easier to land during a crosswind.

Ignition Override
14th Nov 2004, 07:27
No matter what warnings and protections are built into one's plane, complacency can kill you.

This has happened on Douglas, Boeing and even Airbus machines.

A B-757 crew rushed themselves during a typically steep descent and left a charted arrival route in the Andes Mountains. When they were very surprised by the GPWS warning and went to Max Thrust (!), they forgot to retract the speedbrakes. It is easy to forget that they are out in the 757 (they often make no vibration or noise), and crews use them VERY often (SFO/..LAX...ehm.../SEA/DTW/MCO/LGA....).

Even an Airbus factory demonstration pilot at Toulouse pulled one throttle back on an A-330 (with two Italian pilots watching from the jumpseats) and with an autopilot engaged, allowed the plane to quickly climb at a very high "deck angle' and then it stalled/crashed. The main point is that he allowed the autopilot to be 'in command', until much too late. I've never trained on any Airbus, but know lots of guys (a few gals) who fly them.

If anything makes you or the other pilot(s) uncomfortable, switch the autopilot(s) or autothrottles off (did he say that?!) and re-engage the autopilot/flight director system, or whatever you need to do.

Any half-decent training department will give you some exposure to hand-flying any plane without automation being required, in order to get you onto downwind, base then final approach .:uhoh:

BEagle
14th Nov 2004, 08:49
As far as I'm aware, use of FBW in the A320 onwards was for the following reasons:

1. To replace 'natural' pitch stability margins with 'active' control and thus to reduce trim drag, improving payload/range performance.

2. To remove the weight and complexity of 'traditional' mechanical control run (cables, pulleys, cranks etc) input devices to conventional powered flying control systems. This also makes maintenance simpler as everything associated with sidestick to surface is all-electric and provides self-diagnosis.

3. To give envelope protection to protect pilots from themselves at extremes of a/c attitude!

However, although the US has been using FBW in tactical a/c (e.g. F-16) for years, extension of the concept to airliners was viewed with much caution by Boeing et al. Their preferred option was to keep things simple and to use the tried and trusted traditional methods in their a/c. Until the 777, that is.

The side-stick is, I understand, something which virtually everyone who has converted to side-stick prefers just as soon as they become used to the fact that side stick deflexion controls manouevre demand rather than simply control surface angles.

Spearing Britney
14th Nov 2004, 10:53
Bantios, I beg to differ. Airbus sidesticks do not have any synthetic feel, there is no feedback from the control surfaces. The two sidestick controllers are not coupled mechanically and send separate sets of signals to the flight control computers. There is no 'force feedback' system, merely a graduated and invariable resistance to movement that means the sidestick auto centres when released...

As I understand it with the autopilot and autothrust active the yokes on a Boeing move in tandem in response to the autopilots inputs and the throttles move with the autothrust inputs, motors etc making the appropriate motions. I know that in Airbus aircraft neither the sidesticks nor the throttles move when the automatics are in. You can tell what is happenging to the thrust by the display on the upper central screen and can't really tell what is happening to the control surfaces unless perhaps you pull up the 'flight controls' page on the lower screen.

swh
14th Nov 2004, 12:29
I am not aware of any normal cat FAR 25/JAR 25 aircraft that cannot exceed certification limits through misuse of rudder, Airbus and Boeing included.

I am happy to be educated if I am wrong.

:hmm:

Ka8 Flyer
14th Nov 2004, 15:30
Don't know 'bout the A346 (FBW rudder), but on the 'older' FBW airbuses the rudder was indeed mechanically connected, thus there was nothing to save you from PIO's.

Regards,

Mark

TopBunk
14th Nov 2004, 16:05
Having flown both, the major difference between the types is in a crosswind landing.

On a Boeing, using the crab technique, in the flare you kick off the drift and use a little into wind aileron to keep the upwind wing level. Once you have established this into wind aileron position you maintain it throughout the landing roll - especially important in the 747 with it greater swept wing.

On an Airbus, again using the crab technique, in the flare you momentarily push the into wind aileron to say 2 degrees wing down, then release the stick back to neutral, controlling the rudder as normal. [Note the stick is a demand controller in 'normal' law, so if you keep it displaced into wind it will demand a continuing roll into wind]. On touchdown however, everything reverts to 'direct' law, which means that the side stick demand reflects control position, so you have to then move to 'conventional' positioning to keep the wing on the ground.

Personally, having flown both, I like the Airbus FBW protections and auto trim funtions, but would rather have the central control column - because you know what inputs the other guy is making - and moving throttles! However, I would be happier with the Airbus reverting to 'direct' law when the gear is down, so you could handle crosswind conventionally, whilst retaining auto pitch trimming, because the thrust levers remain in a detent, so you are less aware of actual thrust achieved.

alf5071h
14th Nov 2004, 20:09
Ignition Override You selected some poor examples in your post re complacency, particularly that of the Airbus A330 accident. The pilot was the chief test pilot conducting a specific test, the circumstances of which uncovered a design weakness. It is unfortunate that lives were lost to ensure that those who fly Airbus and other aircraft, benefited from the lessons learnt.

Airbus designers appreciated some time ago that the weakest link in aviation safety was the human element. Thus, their designs are human centred, based on the following operational philosophy.

1) The pilot is ultimately responsible for the safe operation of the aircraft. He has final authority with adequate information and means to exercise this authority.
2) The full authority, when required, is obtained with simple intuitive actions, while aiming at eliminating the risks of overstress or overcontrol.
3) The design of a cockpit accommodates for a wide range of pilot skill levels and experience acquired on previous aircraft.
4) The design of a cockpit is dictated by safety, passenger comfort and efficiency in that order of priority.
5) The cockpit design aims at simplifying the crew’s tasks, by enhancing situational and aircraft status awareness.
6) The automation is considered as a complement available to the pilot, who can decide when to delegate and what level of assistance is desirable, according to the situation.
7) The human machine interfaces are designed considering system features, together with pilot’s strengths and weaknesses.
8) State of the art human factors considerations are applied in the system design process to manage the potential pilots' errors.
9) The overall cockpit design favors the crew communication.
10) The use of new technologies and implementation of new functionalities are dictated by
- significant safety benefits
- obvious operational advantages
- a clear response to the pilot’s needs .

Much of the above was validated by Nick Warner; it also reflects the forethought of other pilots such as Gordon Corps. It is regrettable that neither pilot can post their views on this subject, but I suspect that they will have a wry smile from on high as they learn that Boeing has introduced a ‘hard limit’ into the pitch control software of the latest B777-300.