The Lead Computed Gunsight, LCG, is available in the Training arena ONLY, offline or maybe H2H if enabled. It is NOT available in any fighting arenas.
To make it available, from the clipboard goto SETUP and then Arena Settings. IN there you goto Flight Mode Flags and use the Change option. You check LCG and 'OK' your way out of it.
Once available to enable it while flying, and this is based on the TA or offline where you can target friendly targets, follow these steps.
1- Hit 'control-tab' to enable Friendly Lock, system will respond with message.
2- Pick your target. This is done in one of two ways.
2A- Use the 'tab' key to cycle thru all available targets in your view.
2B- Use a 'shift-tab' to choose the target centermost in your view.
The LCG 'boxes' the chosen target icon, similar to a 'check 6 'call, and brings up small green +'s that indicate what lead is required to hit the target. You may see two +'s. This is for your Primary and Secondary gun package.