The biggest thing, but one which you may well want to keep ON, is the pitot heat...15-20A on mine.
In IMC, turning it off could well rob you of the IAS indication pretty quick (minutes) and whether it will thaw later, quickly, and the water drains out, is a good question.
Whether a radio failure is more likely than something else would depend on the radios, I would say. A lot of radios used in GA are old knackered crap. I had a radio failure on one of my first solo flights, during PPL training (bought the Icom A22 the same day).
But that was a typical "training spamcan" radio installation, with a 30+ year old radio, and no intercom. I know a number of small avionics outfits and they spend a lot of their time keeping these early-1970s boxes working, because the owners won't spend money on a new KX155A or whatever.
I've had three alternator failures in three different aircraft.
Never had a radio failure when there was power.
Thinking back to my training, it's hard to say which was emphasised more, but I think it was electrical failure.
In my 2300 hrs of flying, all single engine pistons, I have experienced 5 alternator failures. 4 failures were in 4 different PA-32's. I only have a total of 150 hrs flying PA-32s. Go figure.
(To address the original question: I have had intermittent COM-failures in one specific old COM unit, but never a persistent COM failure not caused by elctrical failure.)
One of the alternator failures were in a Lance (retractable PA-32), in wintertime, at night, in IMC. The Lance had not flown for several weeks and was a little hard to start. It could have been my technique; I had not flown this particular plane for a while.
The failure announced itself clearly wiht a bright low voltage lamp a few minutes after departure. There was no backup alternator, but thinking I had at least 30 minutes of electrical power, I remained sort-of calm, switched off pitot heat and external lights and most of the avionics, leaving, I believe, one navcom and the GPS. I do not remember whether I used the autopilot; I think I did. ATC vectored me back for the ILS, the weather was benign with cloud layers and no ice, and I would be on the ground in less than 10 minutes. Then, when I selected gear down on glide intercept, the panel went dark. Eventually the gear locked down, and I saw three not very bright green lights. When I called again, probably marker inbound, ATC could not hear me. I landed without incident.
I had learned that certification rules call for minimum 30 minutes of battery capacity with IFR equipment running. However, before this incident I never thought about the implication of the battery not always being charged to capacity when airborne. In this case the battery must have been rather low when I took off, being tired from the cold and run down by several starting attempts. It guess it takes at least an hour to charge a battery completely when night IFR equipment is running. In any case, about 10 minutes of IFR flying plus lowering the gear (succesfully, lucky me) emptied the battery.
I learned about flying from that.
Huv,
I have recently been through the certification requirements for this with a project. A battery with only 80% of its original capacity is still considered airworthy, so therefore anything you have better than 80% is bonus, and for certification, you can on;y assume a 90% charge. That means that for battery capacity following alternator failure, you can only take credit for 72% of the amp hours rating for the battery. The aircraft must demonstrate 30 minutes following failure of the alternator, and some of that 30 minutes running the full load, if the annunciation to the pilot is vague. When I did all the math on a Caravan, there was 0.49 minutes excess battery (following the 30 minutes). Not a lot left over!
When I did all the math on a Caravan, there was 0.49 minutes excess battery (following the 30 minutes). Not a lot left over!
Does this apply to a system with 2 alternators, Pilot DAR? I thought almost any PT6 engined plane had a main and a backup "generator".
I have experienced 5 alternator failures. 4 failures were in 4 different PA-32's. I only have a total of 150 hrs flying PA-32s. Go figure.
How is that possible? Was there something common between all the PA32s?
This guy has a 16Ah battery with a 67A total load. How could it get certified? He does have 2 alternators.
Yes, the gear motor will use a lot of power. In a situation such as this one, alternate gear extension might be a real good idea.
I've lost one alternator regulator a couple of months ago but it still had enough power output to drive the GNS430. Everything else went more or less bust. I changed the landing light to an LCD one in the mean time, XPDR is a Trigg TT31 and they both don't give the alternator or battery much of a drain.
Gear and flaps are fully manual in my case, so at least I'd never have a problem with them in that situation. I would not mind however having one fully independent Attitude indicator if power were to leave me at night... I do have 3 GPS's on board of which 2 have batteries for a few hours.
@ Pilot DAR. Thanks for clarification. Do you think maximum capacity percentage is actually measured during the annual performed on piston singles? I suspect many singles might be flying with tired batteries not reaching the 80% mark, with nothing being done about it until it fails to start the engine some cold winter morning.
@ Peter. Nothing in common with the 4 PA-32s as far as I know. Well, they were all rather old, vintages ranging from 1966 to 1977. But so are most other aircraft I have flown. Actually, my total PA-32 hours are only around 120, so I had 4 of 5 alternator failures on a type accounting for 5 % of my total hours. Could be just odd luck, but I cannot help bracing myself whenever I fly PA-32s. I do not think I ever flew a PA-32 at night since then.
@ Mooney Driver. Yes, a timely manual gear extension would have been the right thing to do. But I did not suspect electrical problems before touching the lever. I still wonder what I would have done if gear extension had failed. The right thing, no doubt, would have been to just fly the aeroplane and land, gear up or down or wherever. But when the gear is not securely down on final I guess there is a strong urge to go around and hold while sorting it out. In this case I might not have realized the scenario in time: with a torch in my mouth, no radio and just a handheld GPS for navigation, in the dark, mostly in IMC. A fair bit above my abilities, especially since the ILS would probably have died before I could land. Another tempting option, almost certainly also above my abilities, would have been trying to perform emergency gear extension while flying the ILS.
Since then I always have a small green flashlight glued to the side of my headset whenever I fly in the dark, I always carry a handheld GPS and one or more extra flashlights, and often a handheld VHF also. I had a panel light failure once and the green light was useful. Also I brief myself on the condition of the ship's battery before dark departures.
huv,
Battery capacity is part of the annual in the UK for certain.
The 30 minute requirement seems pretty standard, in the event of a dual gen failure on the CJ2 we have 30 mins with the master in the EMER position, much less in BATT.
