From the second link, >Interestingly the indicators are incandescent bulbs… >an odd choice as they have used LEDs as indicators on the PCBs as we will see lat

From the second link, >Interestingly the indicators are incandescent bulbs… >an odd choice as they have used LEDs as indicators on the PCBs as we will see later. Lightbulbs have well-understood failure mode (open circuit) and detection of such failures; it's exceedingly rare for a lightbulb to fail half-way. Contrast that with LEDs which can fail while remaining as either open or closed circuit. This (costly & lengthy airworthiness certification aside) is why even modern airliners use lightbulbs for avionics indicators - often in redundant pairs. One of very few maintenance items commercial pilots are allowed, and indeed trained, to perform routinely is replacing the indicator lighbulbs. In-depth coverage by Mentour Pilot: https://www.youtube.com/watch?v=RifyTCwwNy0 https://www.youtube.com/watch?v=RifyTCwwNy0