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Circuit Module

Technical Information

Catalogue No: C0499
Category: Flight Control
Object Type: Module/Sub-Assembly/Component
Object Name: Circuit Module
Part No: 250SK17499
Serial No: 001
Manufacturer: GEC Avionics
Division: Flight Systems [FSD]
Platform(s): Boeing 777
Year of Manufacture: 1987
Dimensions:
Width (mm):
170 
Height (mm):
320 
Depth (mm):
10 
Weight (g):
720 
Location: Rack RAA03 [Main Store]
Inscription(s):

Type No. 250SK17499
Serial No. 001

Notes:

This is an I/O (Voltage Mo?) circuit module produced for the Boeing (767X) 777 Prototype. Paper labels stuck to the module read:"MWT1015.1R.2, 250SK-17646".
An FSD tag attached to the module has written on its reverse:
"Boeing (767X) 777 Prototype,
I/O (Voltage Mo?)
Module 1987"

Initial studies of fault-tolerant avionics were conducted jointly with Cranfield in 1984, but the idea had been around in the company since the late 1970s. The research was directed at safety and economy in control, and particularly at effectively zero maintenance.
A Boeing request initiated the work, which had been going on for 21 months, continuing from some Boeing 7J7 fly-by-wire (FBW) prototype studies.
The target was a fit-and-forget electronic flight control system with a probability of total failure of the order of 10 to the power -10, and a 95 per cent dispatch probability even after 30,000 operating hours in situ.
GEC Avionics proposed an FBW control system based on three lanes served by three quadruple-element primary flight control units (PFCUs). Each uses a dissimilar processor, and each runs a software package that is dissimilar from the other two.
The configuration proposed consists of: Inmos Transputer T414 with Occam software, Motorola 88020 with Ada, and Intel 80386 with "C".
Each PFCU and its 12 cards is housed in a 10MCU Arinc 600 box and is to perform under passive cooling up to an environmental temperature of 85°C. The design maximises chip integration, avoiding internal connections, while external connections was minimised; the production PFC card count was reduced to five. 
The primary flight control computers (FCC) – sometimes referred to as primary flight control electronics (FCE) – are located in the aircraft electronic equipment (EE-Bay). Three FCCs are installed on the Boeing 777.
The FCC computes and transmits all normal mode primary flight control surface actuator commands (rudder, elevators, ailerons, flaperons, and horizontal stabilizer as well as the multi-functional spoilers and ground spoilers) to control and maintain normal flight for use by the actuator control electronics (ACE). The 7J7 programme was cancelled but the technology was transferred to the Boeing 777.

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