Originally Posted by EN48
offers potential reliability advantages over mechanical/ electromechanical instrumentation, and the promise of upgrades and fixes via software changes.
Yes, promises. I wouldn't be too sure about either.
Reliability to be proven. But if the glass goes down, everything goes down. With traditional steam gauges, there can't be one single fault that kills all instruments at the same time.
See
here for an updated re-print of a 2014 article from Light Plane Maintenance magazine. While the article mostly speaks about the risk of flying an a/c with a dead battery, further down by way of example, the author spells out the unexpected (or to be expected) effects of an electrical problem on 'modern' avionics. The article concludes with a section called "Is This Progress?".
And promises of upgrades and software fixes? In my experience, these proprietary GPS systems come with high map upgrade costs. I reckon, leaving it (not doing map or required software updates) will render your a/c un-airworthy. So you are trapped.
Given that certified engine and drivetrain technology is in service for 25+ years (very slow rate of innovation), and that electronics show a very high rate of innovation, it seems advisable to reserve as much as possible of that "fast changing feature rich consumer electronics world" to handhelds. Handhelds (be it tablets or proprietary devices, like Garmins) you can change and dump as you feel fit, at much lower cost, and without affecting the airworthiness of your a/c