I think you'll find that Garmin was the 'nav'.......!
558 doesn't need aged old beings to dampen the seat cushions and to understand the ancient electro-mechanical navigation devices which used to live in black dustbins somewhere in the bowels of the jet.
Many a time I recall seeing a RVT whizzing round the peri-track with a replacment 'Calc 2' or somesuch which the directional consultants needed to fettle the NBS. After The Thing was unloaded, there would be a few moments of cursing and swearing from the techies as they fitted it, then murmurs of contentment from the back seats as the navigators got it all working as advertised.