Final answer:
To fly an ILS approach, you typically need to press the ILS button or select the ILS frequency on the EFIS panel, then set the aircraft to navigation mode to follow the ILS signals. The specific procedures may vary, so consult the aircraft's flight manual.
Step-by-step explanation:
If you are flying an Instrument Landing System (ILS) approach, what you must press on the Electronic Flight Instrument System (EFIS) panel can vary depending on the specific aircraft and system setup. However, generally speaking, to engage the ILS mode, you would typically press the ILS button or select the ILS frequency displayed on the radio or navigation console, ensuring that the system is set to the navigation mode which allows the aircraft to follow the ILS signals for both lateral (localizer) and vertical (glide slope) guidance. It's important to note that this process involves several steps, including tuning the correct ILS frequency, identifying the signal, setting the approach course, and engaging an approach mode in the autopilot if used. Professional pilots operate under strict procedures and checklists to ensure all of these steps are correctly followed. Always refer to the aircraft's flight manual for exact procedures.