777 Heathrow crash

[MFAFF]

Jim,

Thanks for the list... but you need to be a bit clearer....there are very few instances in the hull losses listing where the FBW is a primary or sole cause..

However you should also list the LaudaAir 767 loss due to the inadvertent reverse thrust deployment at height...that was an failure that was not prevetned by an secondary dissimilar backup...
The precise cause was never fully established however it does make the point that back ups are not a 'fool-proof' way of avoiding problems.

Or perhaps the Air China 767 at Pusan... another controlled flight into terrain...

[Jim727]

beepbeep's comment was directed at Boeing fbw vs. Airbus fbw, so I selected only fbw. Neither the 767 or 747 are fbw, therefore were excluded. The implication was that Boeing was the fbw screw-up - which is far from clear - so my purpose was to provide facts as a basis for discussion, not to do the analysis, and hull-loss events only to limit the number of events to the most serious.

Jim

[MFAFF]

Ya both wrong anyway...

The 767 has FBW spoilers for both lift dump and roll control... as well as hydraulic actuation of the other control surfaces ( there is no direct manual back up)..ie if your hydraulics fail you lose control, i.e the cable from the flight controls terminates at a hydraulic actuator, whereas the 737NG still has a cable connection to the flying surface (well the trim tab anyway which then flies the rest of it).

So if you lose that hydraulic system then there is a problem and another hydraulic system needs to be used and as you know losing a hydraulic system is not somehting that passes unoticed.

And the 777 is not solely FBW it still has the same type of 'manual reversion' that the 767 has.. the 787 will be the first completely FBW Boeing airliner...

From what I 'read between' the lines of your responses Jim I think the issue is not whether or not its an FBW system or not, or even if there is a dissimilar back up system.. its more basic than that...its one of who is actually flying the aircraft..

With FBW the real FBW, the pilot tells the computer what he wants the aircraft to do and then its the pre programmed system that works out the more efficient/ effective/ easiest way of achieving that bearing in mind what it knows about the plane, its perfromance limits and the current situation...so if the pilot wants to climb in a 'traditional' aricraft then the pilot deceides the mix of pitch up, added power/ flps etc needed to achieve those aims..in an FBW one the computer makes that call... the pilot is effectively giving commands to the electronic crew.

Now that is a perspective that many find unaccpetable and understandably...but its is not better or worse.

BTW in the A320 FBW systems there is a 'Direct Law' mode which by passes the computers and permits a limited direct control of the flying surfaces by activation of the flight control actuators...thus total computer failure results in limited flight control ability but not total inability to move the flight controls.
Direct law has not been used in service in the A320.....Now I believe that more recent Airbus (A330/A340) have omitted this mode.. but not certain..)

I believe the 777 FBW system has a similar mode..

[Jim727]

Well, yes and no.

First, I have no direct experience with the 767 flight control systems, so I will have to make some inquiries or hope someone with direct systems knowledge can fill that bit in.

Second, I think we are a bit crossed-up on definitions. So...

"Manual Reversion" is a direct (cable-and-pulley) connection between the cockpit flight controls and the aerodynamic controls, usually by operating "tabs" on the aero controls. Hydraulic actuators are not manual reversion.

"Fly-By-Wire" is any system which requires the presence of electronic/computerized processing between cockpit control inputs and movement of flight control (or other) surfaces.

"Direct Law" is fbw in that it is still a system in which the pilot's input is processed as a request to the flight control computer - it does not bypass it. The pilot may, for example, request bank and pitch to "manually" intercept a course rather than dial in the intercept and letting the computer do it, but it is not by any means bypassing the computer(s).

The last time I was in the cockpit of a 320 (firmly on the ground, I might add) the only available flight controls were the joysticks and a pitch-trim control. The crew was unable to direct me to any non-computerized methods of operating the aircraft. When pressed with the question of how to operate the a/c when complete computer failure occurs, the answer was "It will be a hell of an airshow".

I'm a bit surprised my position seems hidden "between the lines". I have made no secret that I have no inherent problem with fbw but have major problems with any flight control methodology that does not provide an alternative (meaning simpler and different) method of controlling the vehicle as well as any system which overrides the pilots.

My problem with lack of a fallback flight control system applies equally to aircraft such as the old DC-10 (remember UAL 123?) as to similarly vulnerable fbw aircraft. The C-17 is fbw but it has true manual reversion; the best of all worlds. I also vehemently disagree with any system that gives priority to the automation over the crew's inputs (though in some parts of the world I confess I would prefer the automation). Automation-priority is not only unacceptable it is definitely worse.

Jim