Complex sentence: The average transport aircraft in the mid- 1970s had more than 100 cockpit instruments and controls, and the primary flight instruments were already crowded with indicators, crossbars, and symbols, and the growing number of cockpit elements were competing for cockpit space and pilot attention.
Split into simpler sentences: The average transport aircraft in the mid- 1970s had more than 100 cockpit instruments and controls, and the primary flight instruments were already crowded with indicators, crossbars, and symbols. In other words, the growing number of cockpit elements were competing for cockpit space and pilot attention.