I was concerned about the possibility of a single-point-of-failure in the SR22’s electrical system. I know how hard it can be to be sure there isn’t one. So when I was in DLH, I spoke with the fellow, a Mr. Crawford, who designed the MCU. The MCU controls both electrical systems. He convinced me that they had at least given the subject some intelligent thought. But that doesn’t mean that there isn’t a single wire that couldn’t take out the whole electrical system.
Btw, Cirrus has had q/c problems with the MCU. THey are bringing production in-house to try to solve these problems. My a/c is on its second MCU and probably needs another one. The symptom is that sometimes in hot weather, the ALT 2 light will flash and the ALT 2 current will spike to maximum deflection. Yet, the bus voltage is normal and ALT 1 current is normal and no CB’s pop. So it must be the current sensor for ALT 2 and this is in the MCU. Also, pop’ing the ALT 2 CB and turning off ALT 2 have no effect on the max-current indications, but one can see the effect of turning off ALT 2 by the slight increase in the ALT 1 current as ALT 1 picks up the load.
Last Monday, on departure from PWK (Palwaukee, just north of ORD at Chicago), I suffered a complete electrical failure shortly after takeoff. I was on an IFR flight plan, although fortunately I was still in VMC when this happened.
The problem turned out to be a connector which carries the ground connections from all the cockpit electronics (avionics, Battery Master switch, etc.) to the Ground Buss bar mounted on the engine side of the firewall. The connector is located more or less opposite the copilot’s left knee. It’s held in by a couple of screws which vibrated loose. The result was that everything switched off.
The fix was simple - tighten the screws. I’ve been told that there’s a good possibility that my airplane is missing some nylon capture-nuts that would have prevented this from happening. I’ll check on that at the first opportunity.