HSI Tech
While the HSI was a game-changer for the instrument pilot by raising the bar on situational awareness, it introduced more avionics complexity, especially when connected to multiple nav sources. In failure mode, and for the pilot who doesnt know how to operate it, the instrument can be a killer. When I was a new avionics technician, Narcos DGO-series HSI system was the ground breaker. But, not all pilots fully understood what an HSI would do, and fewer yet understood how they worked. Thats somewhat true even today.