In a message dated 7/20/2003 6:08:30 PM Central Daylight Time, RWolf99@aol.com writes:

Yes, this is fine while the co-pilot sorts out the electrical mess.   The FARs, for what its worth, don't fly.  It is ludicrous to say that the FARs only require you to fly VFR after an electrical fire - How do you get out of IMC whilst suspending the IFR flying? Huh? Huh?

 

Now, let's go back to the purpose of an essential bus in Part 21 aircraft not designed by a committee, the FARs.  Should a catastrophic electrical emergency occur, what does a single pilot IFR operation need to safely get to the ground within some time frame, say 45 minutes?  What are the likely items to help this out, but may be eliminated if they are a problem - either the root of the problem or drawing too heavy of a load on the battery, depending on day or night operations?  Let's try an example that everyone can take pot shots at, my wee aeroplane.

 

1. Approximately 40 circuits are protected, 18 by resettable breakers, 18 by ground changeable fuses and several by inline fuses because of the power source.  The fuse protected circuits are those that make no sense to try to reset.  Besides that, there wasn't enough room for 36 breakers on my panel.

 

2. Items of interest on the main circuit - heavy loads and various cute time passers.

Of some concern is that the master relay becomes fused in the closed position and a short occurs on the #4 power line. Luckily, we are flying in an insulator and properly routed main power and ground leads should virtually eliminate this potential problem (no pun intended).  All the other lines are protected.  There is one exposure in that the line to the starter could short in the engine compartment but that is only a concern when the starter power is engaged and I have an indicator for that.  Some other major electrical problem among the heavy users can quickly be eliminated by turning on the essential bus, turning off the master and pulling the field circuit breaker.  Now what am I left with?

 

3. Essential bus items include:

Landing gear down and locked lights,

Electric turn coordinator,

Backup electric air data device (Rocky Mountain Instrument micro-encoder),

Engine instrumentation,

Cold-cathode low-draw panel floodlight,

AOA,COM1, GPS, NAV1 (all in a Garmin 430) and Transponder.

 

These were listed in order of importance and most are controlled by breakers.  Sometimes people ask "Why the Transponder?"  It is easier for ATC to keep track of me, after I declare an emergency, while the transponder is on.  If I am at a low altitude west of the Mississippi, I would probably turn it off.  Why don't I need the wing to header fuel pumps?  Because my automatic fuel system keeps the header tank above 8 gallons, more than enough for 45 minutes.  Why the GPS?  Because it is the single pilot's friend.  If any of these systems becomes a problem, its' power can be shut off at the breaker.

 

4.  If a cool head can determine what main bus component caused the catastrophic electrical failure, perhaps it can be isolated via breaker and certain main bus services restored, like the alternator, by re-powering the master relay.  Otherwise, lets look at what is now unavailable.

No boost pump - I ain't going around in this condition anyway and I don't care if the engine stops once the runway (road, field, back of a flat bed truck) is made.

No flap motor - OK, I'll land faster if last minute re-powering the main bus is a problem.

No gear pump - Lets see, the last time I practiced the emergency gear procedure was?....

No sound canceling headset, no COM2, No ADF, No Auto Pilot - So what!

No landing light (I close my eyes anyway), No Nav lights (so arrest me, please!),

No strobes, no instrument lights (see #3),

No electric trim (elevator is manual/spring trim controlled)

No automatic header tank fill system - That's OK, I've got enough to get down.

No alternator, No defrost fan (Hmmm), No starter (Well Geez), My Hobbs meter will stop.

No curb feelers, no horn, no turn signals - Gasp.

 

Well, in these circumstances, maybe my vacuum system still has the gyros erected.

 

I ain't shooting no zero-zero approaches without all my stuff and my blanket!

 

Now, Rob also noted:

 

....
this backup mode as an average spam can has in it's primary mode. 

 

Well, most spam cans were certified before modern electricity came into existence.  The 73 Skymaster I flew had two alternators/regulators that were confused about just who was the primary - hence the famous "flickering light" problem and its ability to hypnotize you into believing the plane was fast.  Note that all the interior lights were on the same circuit breaker - interesting when a weird intermittent short would take out the lights over Chattanooga at night.  Luckily, the ice light (different breaker) out on the pilot's wing would provide enough light to read the instruments and the latest Ian Fleming Bond novel.

 

OK, fire away.