Originally Posted by spannersatcx
They're not LED's they are normal filaments.
Modes are displayed on PFD.
Thanks - the pictures have insufficient resolution for me to tell that they are filament bulbs rather than LEDs.
Am I right in thinking that on pressing a button to switch on a mode, the button lights up (what color?), the PFD displays a mnemonic to indicate that the mode is either armed or engaged - it's a Rockwell Collins Pro Line PFD, isn't it? - and the light in the button remains on (same color) until the button is pressed again to disengage/disarm the mode, or until another incompatible mode is selected/engaged. If the mode is initially armed, the indication that it is engaged is announced on the PFD.
I am familiar with the Collins Pro Line 4 annunciation of autopilot modes in the Learjet.
Thanks to everyone for helping me out.
Nick