Electrical failure has happened to me twice now - once a complete and total failure when still on the ground, just prior to run-up. Secondly, when airborne VFR and the battery ran down over 20-30 minutes.
What's quickly apparent is just how much of the avionics relies on electrical power. In this recent case, the Garmin 430 was providing both radio, en-route navigation and potentially instrument approaches if needed. After switching itself off and on, it became clear that neither it nor the other radio transmitter were operating. I very much doubted that the transponder was still working (light not flashing), so setting 7600 probably didn't make any difference. I was able to return to an uncontrolled airport and land, listening out for other traffic on COM2 which I would have heard but not been able to respond to.
It's made me much more aware of a) the idea of carrying a portable transceiver b) the helpfulness of having some backup navigation that uses batteries (especially if in IMC) c) reminding myself what the radio failure procedures and signals are
I've also heard of others suffering similar electrical failures, due to alternator failure. By comparison, I think its very unlikely that both radios would fail simultaneously. Perhaps some finger trouble (eg turning down the volume, not switching between radios properly), broken PTT button (have seen that happen, but not on both sides simultaneously), or even headset issues are all potential cases.
I recall that the G1000 glass cockpits have their own built-in batteries which last for an hour or two. I suspect that these won't power the transponder though, and probably not the radio either.
My conclusion is that electrical failure is much more likely. Light signals and radio failure procedures are relevant, even where the 7600 squawk might not work.
Do you think PPL (and/or IMC) training should prioritise this scenario above radio failure alone?
Any transition training should cover the electrical system. Can't see it making much sense in the PPL as every aircraft is different.
Yeah I've had a few electrical failures, though I've never had a working com quit while it still had power. I do carry a portable, though it is nothing like the old Narco portable I used to use. I had it connected to a second comm antenna on the roof when in use. It would operate to a ground station 50 miles away if you had the altitude. The Vertex I have now struggles to transmit 25 miles. I don't depend upon it for more than that - though I only fly VFR, and generally to uncontrolled airports anyway.
Interestingly, when recently doing a mod approval on a Caravan, we did a very detailed electrical load analysis in accordance with the Caravan maintenance manual. Assuming the pilot noticed a complete charging failure within 5 minutes of its occurrence, night IFR, but not in icing, there would be a total of 30.5 minutes from the original failure, to the battery being below a useful threshold. Not much margin....
There are standby alternator systems for singles. Those little pad mount 20 amp alternators are handy, but you have to have a properly arranged system. If you're pulling 40 amps, and you spit off the alternator drive belt, that 20 amp standby might try to pick up that load, before the pilot can shed it. Overloading the 20 standby alternator is a real possibility. There are special circuits to manage this. I designed one for the turbine DC-3 I work on. With 180 amp project power circuit, the second generator cannot withstand that load, and the basic aircraft load, if one alternator quits. So I required an automatic project power shedding circuit, and magnetic release switch for that circuit, which the shedding circuit could open without pilot action. It all works great.
Aircraft are happily demanding less power to run the basic systems these days, and LED lights really help! But, yes, be prepared, electricity does stop flowing from time to time.....
Supporting JasonC's post, the scenario described is standard procedure when I fly my simpler aircraft: no alternator or battery installed, operating out of a Class D airspace airport, using a handheld for communication with no transponder. Navigation is by handheld GPS and pilotage. I was taught in Private Pilot training with that aircraft that Option 1 if the handheld radio failed is to circle above the Class D until getting a green light. Option 2 is diverting to a non-tower airport, and Option 3 (last resort) would be to blend with traffic, land and explain later.
Flying my other more complex aircraft, my bigger concerns with electrical power are control of the electric propeller (particularly) and the flaps, versus communication issues.
IMC makes for much more difficulty but is not greatly relevant for initial Private Pilot training.
This used to be a major issue but in my view it isn't today. Everybody got a smartphone with GPS and can install some sort of navigation software. The only thing you need to buy is a transceiver.
My glass cockpit (Aspen) got its own 30 minutes backup battery which mainly targets a complete breakdown of the electric system (including battery). Also I've got numerous warnings when voltage drops so the frequent issue of the pilot not noticing a dead alternator isn't really an issue. One has to react quickly and perform load shedding. The power hungry transponder would be the first thing to kill.
Is electrical failure more likely than radio failure?
Yes, this comes as a natural fact, because (almost) every electrical failure causes a radio failure as well!
Do you think PPL (and/or IMC) training should prioritise this scenario above radio failure alone?
For PPL it is not so important, but for IMC/IR it must be part of the training program. In our FTO, we do it in the procedures trainer. Apart from the radios, every other electrical system will be affected as well, like landing gear, pitot heater (important in actual IMC) and other anti-ice systems, stall warning, flaps, ...
So far, I had several single radio units fail and two total electrical failures, one of them in a twin. Having two generators reduces the risk of failure, but it does not eliminate it!
The power hungry transponder would be the first thing to kill.
I was wondering to myself whether in a diminishing power situation whether I would prefer to kill the transponder first, or the comms radio. Once I had got a Mayday call out, I'm thinking a transponder may be more useful as it would allow my position to be tracked and help diverted to me more precisely should I need it.
I'm thinking a transponder may be more useful as it would allow my position to be tracked and help diverted to me more precisely should I need it.
Once you are in distress, ATC will mark your radar target and have a guy track you fulltime. The transponder only adds altitude but that is not really that important because you will surely have your own means for avoiding terrain and ATC will in any case make sure that there is a lot of sky around you in all directions. A transponder constantly transmits at high power whereas a COM only needs a lot of energy when you transmit.
I have done IFR flights without transponder because it was broken and I have asked ATC for permission before getting my IFR clearance. It's just additional workload for them because they need to spend more time looking at you and keep asking you for altitude.
The power hungry transponder would be the first thing to kill.
We've had this in an earlier thread already and I looked up the specs. A modern solid state Mode S transponders consumes 300mA at 12V or 3W. It transmits pulses of high power, but they are of very short duration, so the total power consumption is very low!
Every bulb of your nav lights is rated at 25W in comparison. Leaving the nav lights on consumes 25 times more electricity than the transponder.
So unless you have an antique steam driven transponder (with heated vacuum tubes) you really should leave it on for the sake of the traffic around you. Not only ATC is intersted in your position, but every TCAS equipped aircraft as well!
You're right, the values for mine (TRT800A) are:
0,20 A @ 27,5 VDC (typ.) 0,35 A @ 27,5 VDC (max.) 10 W (max)
