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My Cessna 172 SP's alternator died while stationed at a class D airport, less than 10 miles from my home field (another class D). Both airports are within the mode C veil of a nearby B airport.

Assuming that I fully charge my battery before flying to my home field for repairs, it seems to me that I can do so in full compliance with regulations. I'll fly VFR during the day, and plan to only keep my beacon (anti-collision), transponder, ADS-B out and one radio online, and shut down all other electrical equipment to make double sure my battery will have plenty enough for the flight. I'll also carry a battery-operated backup radio just in case.

My question is: am I right in assuming that I'd be perfectly legal taking this short flight? Or do I need a ferry permit from my local FSDO?

Pondlife
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user4867444
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  • No A&P able to travel to the aircraft? – Ron Beyer Jul 19 '21 at 15:19
  • That's a bad idea, even if it's legal, deep-draining a battery is a good way to ruin it and cost you more money. If you're so close to your home base it shouldn't be hard to get an A&P to replace it – GdD Jul 19 '21 at 15:19
  • A&Ps are in short supplies around here, and not lacking for work at all. So traveling to a plane is a deal breaker for most if not all of them; I've had no luck finding any so far. – user4867444 Jul 19 '21 at 15:21
  • And it's less than 10 miles flying, but it's on the other side of a lake, with a big city in the middle, driving. Usually 40-50 mins with traffic, so my usual A&P isn't too keen on making the trip. – user4867444 Jul 19 '21 at 15:25
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    Welcome to aviation.SE! I think the real question here isn't about the mode C veil, it's whether a C172 with an inop alternator is airworthy. – Pondlife Jul 19 '21 at 15:53
  • @Pondlife I do think the mode C is relevant. If it wasn't for that, I would only need the beacon to be legal, and use the backup radio for comms; so I wouldn't really think twice about it. – user4867444 Jul 19 '21 at 16:03
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    ATC can issue you a clearance or waiver, call them up and explain what you need to do, chances are you'll be told to go ahead but coordinate with them. – Ron Beyer Jul 19 '21 at 16:44
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    @user4867444 Well, if the alternator is required for the aircraft to be airworthy then you'll need a ferry permit in any case. That's why I'd start with that question and go from there. – Pondlife Jul 19 '21 at 17:26
  • @Pondlife fair enough :) C172s don't have any KOEL or minimum equipment list, so the only thing that applies for day VFR flights is the old ATOMATOFLAMES. As long as the beacon is on (anti-collision), it doesn't need anything electrical on to be legal. – user4867444 Jul 19 '21 at 17:30
  • @user4867444 Some C172S models do have a KOEL, and it lists the alternator as required for day VFR. Yours may not, of course. – Pondlife Jul 19 '21 at 18:01
  • @Pondlife I stand corrected, my bad. Just double-checked mine's POH though, no KOEL. – user4867444 Jul 19 '21 at 18:48
  • If you don’t have a working alternator I don’t see how the airplane is airworthy. You can mark some things as inop, but I can’t imagine that an alternator would be one of them. §91.7 (a) No person may operate a civil aircraft unless it is in an airworthy condition. – JScarry Jul 20 '21 at 18:31
  • @JScarry how do you come to that conclusion? What if the fuel will run out before the battery does? Many planes do not have alternators and simply charge their battery on the ground, e.g. aerobatic planes where the weight is considered a liability. – Kenn Sebesta Jul 20 '21 at 20:26
  • @KennSebesta The plane was certified with an alternator. Not having a working alternator would mean that it doesn't conform to it’s type certificate—hence unairworthy. Unless there is a KOEL that says that you can fly without it, my default assumption is that it’s required. If anything bad happened on the flight §91.13 Careless or reckless operation. would probably apply too. – JScarry Jul 20 '21 at 20:56
  • @JScarry I see your point. Since we know it's not on the MEL and there is no KOEL, then these do not limit the poster. In the absence of those two lists, https://resources.savvyaviation.com//wp-content/uploads/articles_eaa/EAA_2011-09_too-broken-to-fly.pdf gives a very good breakdown of determining which equipment is necessary to be considered airworthy. https://aviation.stackexchange.com/questions/72207/is-it-illegal-to-fly-a-cessna-172s-under-day-vfr-with-an-inoperative-vacuum-gaug asks a similar question. – Kenn Sebesta Jul 20 '21 at 21:20
  • This might also be relevant to understanding whether the specific plane in question is airworthy with an inop alternator: http://www.aviationattorney.com/publications/lawfully-operating-%E2%80%9Cunairworthy%E2%80%9D-aircraft – Kenn Sebesta Jul 20 '21 at 21:34
  • @KennSebesta I don’t think the autopilot issue is on point. Mike Busch does point out that “If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in accordance with Part 43 of this chapter;” so if you can persuade an A&P to sign off on a faulty alternator or remove it before flight then I suppose you would be satisfying the letter of the FARs. I’m fairly certain that my A&Ps wouldn’t sign off on that without figuring out why the alternator wasn‘t working. Was it really the alternator, something else in the circuit, the gears? – JScarry Jul 20 '21 at 22:21

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No, you do not need a ferry permit to fly without the transponder[*]. If you wish to fly inside the Mode C veil, it is sufficient to reach out to ATC and ask for permission. For a 10 minute flight that stays low to the ground, I'm sure they'll be happy to help. It makes it easier on them if you can fly when they aren't slammed, but since you're not in their airspace, they are pretty understanding.

You might be surprised by the number of transponder-less aircraft flying under the Mode C veil: lots of old planes which never had electrical systems, lots of new ultralights, and there could even be gliders around. You won't be the only one up there without ADSB-Out.

FWIW, I expect that your plane can fly quite some distance with everything off but the transponder. They typically consume 10-20W, so you should have several hours' worth of energy.

[*] In general flight without an alternator might not be allowed, though. This depends on the Comprehensive Equipment List, or Minimum Equipment List, or Kinds of Operation Equipment List, or basic certification standards in effect when the plane was certified. If the alternator for your specific plane is on one of those lists as required equipment then the plane would be considered not airworthy and would require a ferry permit.

Kenn Sebesta
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