Why do companies buy aircraft with different impedance avionics systems? It's more expensive in the long run, since two sets of parts have to be kept in inventory, and it's a PITA for all involved. Why not just get the proper avionics in the first place? Here only the military uses low-impedance avionics, and that is purely a matter of inertia, since there are no technical reasons. I've never seen a civilian aircraft with low-impedance avionics, and I'm curious as to why they're in use elsewhere.