The green 'Go' configuration light depends on the following flowchart:
Ess 28v DC Busbar -> Fwd Thrust Selected -> Arming Switch 'On' -> Landing Gear Relay Operated -> Fuel Flow Attained -> Jet Pipe Pressure (P7) Attained -> Bucket Position Correct -> 'GO'.
How were these engine parameters monitored? (From the AMM)
- Arming Switch 'ON' : it's a manually operated four-pole solenoid-held switch, for the four engine circuits, operative only when a landing gear weight switch is energized.
- Fuel Flow and Jet Pipe Pressure (P7) Attained: Once the circuit to the 'Go' light is armed, the flow and pressure are monitored against the values set on the indicator bugs on the respective instruments. Once they pass those values, their respective change-over relays are energized, completing the circuit.
Here's a simplified schematic for this:
At least I think that's how it works
.
Lefteris