I take it then you are programming the approach, glide slope, approach speed yourself. I have a cousin the works for Garmin aviation division in Virginia and it truly amazes me what what they can do today. If I were a young man and had the aptitude for it I would get into software engineering. Keep at it your doing a great job. From what he has told me the computer flight control systems can handle just about any situation they are programmed for, he said the problem comes when a problem is encountered that the flight systems are't programmed to handle.
Yes, our lab at the U of MN has developed our own inhouse flight control hardware and software to support our various research projects. So for the autonomous landing stuff, I've programmed and set that up all myself (along with testing, tuning, and occasional mishaps.) I probably started messing with autoland 6-7 years ago and the code/strategies have been evolving and improving ever since. Also the augmented reality HUD and visualization I posted above is all developed in house as a tool for seeing what our autopilot is thinking and doing ... but when we get out at dusk, it also makes for cool videos.
Our systems intentionally try to keep things simple. Other people can do everything for everyone on every kind of computer board, sensor, and vehicle. We try to narrow our focus and do a good job at just a few things. Our system pretty much assumes all the sensors will be working correctly. We have a ground control station with a bunch of gauges and data so hopefully in many cases, the operator can see a problem with a bit of advance warning before it goes flight critical. If something does completely fail, then we refer back to our definition of line of sight (we can see the speck and see it well enough to judge orientation and manually fly like an RC airplane.) At that point it's up to the pilot on the ground to take the best action possible and hopefully save the airplane (with the highest priority of course being the safety of the people.)
I've had an elevator servo fail hard over (full up elevator). That led to the expected stall, plunge, stall, plunge sequence ... I manually took over control of the airplane and did my best to roll the airplane 90 degrees knife edge at the peak of it's stall and then roll back level as it started to plunge ... this got me a little bit under control. I timed the last stall just right and plopped the airplane down right at my feet. Now every time I crash a plane doing something stupid, I think back to the one time I got lucky (or good?) and actually saved the airplane. So I remember I even have video of that flight ... jump to about 8 min 20 seconds into this video to where the issue starts:
A few months later I had a similar servo failure on one of the aileron servos. In that case I figured out something was really wrong, tried to fly it manually but completely failed, so I put it back on autopilot and that was successful enough to get the airplane back closer at which point I took back manually control again and sort of flopped it into the bean field next to our club field. Fairly minor damage.
So the moral of the story is this: the fancy $2.87 digital servos from hobby king (versus the $1.98 analog servos) still are terrible. It's worth spending money on quality components and tossing anything that is even slightly suspect. In both cases I was flying a $1000 camera on board ... so why risk that to save a couple bucks on el cheapo servos? I dunno ... I knew better and did it anyway and got sort of lucky, but ended up needing to replace the servos with better ones anyway.