'Amplifier Filter Low Pass' Circuit Module

The BAC 1-11 AFCS, like that in the VC10, was based on the well proven Bendix PB-20 Autopilot and was designated the Series 2000 AFCS. New features over the PB-20 system include separate pitch and azimuth control computers, a modular Air Data Sensor and a range of units specifically designed for autoflare and autolanding.

Each unit in the BAC 1-11 AFCS is built to a common configuration with circuit modules arranged in stacks either side of the chassis. The stacks are connected by plugs to a mother board and are physically separated into ‘command’ and ‘monitor’ functions to preclude common failures. The computers are entirely solid state and there is a high degree of built-in-test. Self-monitoring techniques and multiple channel redundancy are used to give automatic failure survival in approach and cruise flight.

These circuit modules from the VC-10 computer are typical of construction techniques of the early 1960’s to early 1970’s. The technique of building up electronic and electro-mechanical units in plug-in card modules was a feature of the Bendix PB-20 system Autopilot upon which the Elliott system was based. A number of these cards and modules are common to a range of boxes. However, Elliotts also designed many of their own cards and overall the Autopilot has some 25 different types.