Re: Boeing 777 - Totally Irresponsible?

Date:         07 Jan 97 07:20:18 
From: (Kieron Murphy)
Organization: REIWA
References:   1 2 3 4 5
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"Peter Ashwood-Smith" <> wrote:

>   One way to make the single CPU/single module system very
>reliable is to properly isolate all tasks with fixed CPU bounds
>on each task, fixed memory bounds etc.

>   I don't know what approach is taken with the 777 and Airbus
>software but I sure as hell hope the modules are either physically
>isolated (separate CPU/memory) or totally logically isoated with
>fixed CPU/memory bounds.

>   Anybody know for sure what kind of architectures the Boeing
>and Airbus systems use?

Here's some info on the 777 FBW system -

3 GEC-Marconi Avionics primary fligh control computers
Each computer has 3 different computing lanes and each lane has it's
own processor, power supply and link to the 777's data bus.

Each computer/lane read imputs from the stick checks itself and the
other two counterparts and if all agree the command is sent to the
actuator control electronics (ACE), if one doesn't agree it's
overruled by the majority of lane's.

Originally 3 programming teams where going to be used (as does Airbus)
however this was abandoned as the advantages of seperate teams was
being eroded due to similar logic cropped up in each team.

The 777 is governed by 'speed stability' meaning the aircraft is
trimmed to a particular speed and any alteration from this speed will
cause a change in pitch to compensate. (The Airbus is governed to
maintain pitch)

If the computer suffer a total failure, the ACE's can be used to
control the plane. If everything fails in the FBW system their is
mechanical links to hydraulically controlled trims in the horizontal
stabiliser and a cable driven spoiler on each wing.

There, do you feel like flying on one now :)
(not aimed at anyone in particular)