That's AIM 6-4-1 (which quotes FAR 91.185 and adds). As I was mulling over the consequences and procedures for electrical failure, I wondered how I would get the airplane back on the ground at KAUS, which is a Class C airspace that requires two-way communications.
If the conditions are VFR, you maintain VFR and land as soon as is practicable. This allows the pilot discretion beyond "as soon as possible" to select a suitable airport or continue to the intended destination if it's close. The idea in general, though, is that if ATC can't contact you and/or you can't respond, you're the jerk screwing up the airspace for everyone else.
To land VFR at a non-towered field is a simple matter of good judgment. Fly over the field to assess winds and traffic, then fit yourself into the traffic safely and land.
If, however, the conditions are IFR, it's a little more complicated. Assume it's all clouds. What do you do? First let's think about just radio failure, not full-on electrical failure (so you still have your transponder, which it says to set to Mode A/3 squawking 7600; does Mode A/3 broadcast altitude?). The AIM section says:
- route assigned in last clearance
- if being vectored, go direct to the next fix/route/airway in the clearance
- route ATC said to expect
- route filed in flight plan
- Altitude - highest for current route segment
- altitude assigned in last clearance
- minimum altitude for IFR operations
- altitude ATC said to expect
The ideas here are to be predictable to ATC. There is likely to be confusion when you don't acknowledge or heed instructions (note to self: this is one reason it's so important for me to respond right away even if I have to ask to repeat), but if you move along in a predictable fashion, they can plan around you. Again, if you get to VFR conditions, land.
What if the failure happens before your approach but it makes sense to try the approach? First, this seems pretty risky to me since you have no way of knowing whether the airspace is clear. Second, however, you've been acting very predictably so perhaps you can go for it. The AIM instructs to start the descent/approach as near as possible to the expect further clearance time (if received) or the expected arrival time, keeping you predictable.
Assuming it's just a comm radio problem, consider using the nav radio to contact FSS on a VOR that can receive. AIM 6.4.2 talks briefly about having them relay situation reports and clearances.
FSS gives in-flight weather, too. Imagine being in IMC with no radios, headed straight into some nasty weather? (And the Stratus/SXAR1 ran out of battery. Or the iPad died.) Egad, man.
Suppose we were to lose comm while still inside KAUS airspace. I believe we would have to maintain the last clearance (which generally is sending us out of the Class C) and stay out. There are procedures for rocking wings and flashing lights to communicate with Class D towers, and they use a light gun where certain colors/patterns mean different things (solid green means cleared to land, flashing red means unsafe airport, etc). If we were outside the airspace, we couldn't come back in: Class C airspace requires two-way communications and Mode C transponder. (I would think losing transponder in their airspace but maintaining communications could be dealt with to allow us to land.)
So, that's when radios fail when flying IFR in IMC or VMC, but ATC can still see you on the radar. What about full electrical failure? No comm and no transponder, so ATC doesn't know you exist, although hopefully they're concerned that you disappeared. I'm getting sweaty palms just thinking about it.
I'll take a guess before I look it up. If it's VMC, land. If it's IMC, get to VMC safely ASAP. So where is VMC, and how do I get there safely? Having briefed the route, we should have a good idea of what the weather systems are like along the route (and ForeFlight + external device(s) is indispensable in a situation like this). Turn back? Proceed with a deviation? Could descending to an MEA (or even a MOCA?) or climbing to an altitude (VFR, I assume) appropriate for our heading get us to VFR? Do any of these options have a high likelihood of success with a low chance of compromising separation? Do we pick areas away from airways or routes between waypoints (harder with GPS waypoints all over the place)?
In IMC, this is all risky business; who knows who else is out there! Intermission now for dinner...