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Today I had rented a Piper Archer III for a local flight. After taxing to the fuel and filling up, I went to start the plane again and it did not want to turn over. This particular plane is somewhat fussy and sometimes doesn't start right away. As I continued to crank the engine over, you could tell the cranking lulled and the battery was having difficulty turning the engine over as effortlessly as it typically would. At one point the prop wouldn't even rotate.

I eventually got the plane started after a series of cranking / resting periods. I made the decision to not fly given the battery issue and returned the plane to its hangar.

The owner of the flight school was initially reluctant to comp the 1/3 of an hour I had on the hobbs (from taxing to gas pumps, etc) stating that once I had the plane started, I could have flown since it would have been powered by the magnetos.

My question: I know that the plane is powered by the magnetos once started, however, was my decision to not fly unfounded and unnecessarily cautious or would there be good reason not to fly knowing that the battery was weak and unreliable?

Update: It seems that some answers and comments have a focus on the financial aspect of my question. To be clear, this is not about money or how much. No one should pay for goods or services that were not rendered. The FBO's argument was that the choice not to fly was my own and not due to a responsibility of the FBO's to fix a "broken" plane. The money aspect is just an indicator of where the responsibility lies, on my shoulders or the FBO's.

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    $\begingroup$ While it’s not necessarily unsafe in VFR conditions, it’s never a good idea to take off with some degraded system. What if the alternator failed or the alternator wire broke? It happened to me before and I took off not knowing it or recognizing it. 15 mins into the flight avionics started shutting down. No fun. I would have aborted too and the owner is potentially suggesting bad airmanship if saying you should have flown. That said, the financial aspect is another matter between you and him. $\endgroup$
    – Pugz
    Jan 30, 2018 at 2:59
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    $\begingroup$ How much time was spent cranking? Did you perform a hot start or attempt a normal start? The owner may be very experienced and knows that the flight would have been safe, hence his frustration. That said, you were PIC and made the safe decision. $\endgroup$
    – acpilot
    Jan 30, 2018 at 3:17
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    $\begingroup$ Is "battery" on the aircraft's Minimum Equipment List? It's on my car's. Also, are you in the Northern Hemisphere? $\endgroup$
    – Harper - Reinstate Monica
    Jan 30, 2018 at 18:03
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    $\begingroup$ I wouldn't even do this in a car, for goodness sake! $\endgroup$
    – Fattie
    Jan 30, 2018 at 18:22
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    $\begingroup$ If the battery wasn't charged there's a possibility, depending on the electrical design of the aircraft, that the magnetos themselves were fried which could have been catastrophic depending on which stage of the flight the battery became unable to keep a spark. I had this problem with my old motorcycle. Here's an exact quote from the manufacturer's preflight checklist for that aircraft, "DO NOT ATTEMPT FLIGHT IF THERE IS NO INDICATION OF ALTERNATOR OUTPUT". A dead battery is the strongest sign of no alternator output. $\endgroup$
    – Noah Wood
    Jan 31, 2018 at 6:16

6 Answers 6

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First off, you absolutely made the correct decision. As PIC/pilot you have not only the ability, but the duty to call off any flight you don't feel comfortable regardless of the reason. Your go/no go decision can be based off of anything and you should always be comfortable making that decision.

Now as far as the battery goes I can tell you I was in exactly this situation a couple years ago with a rented Piper Comanche. It was cold out and the start attempts completely killed the battery. The FBO (also the owner) decided to jump it using a start cart and got it going. They comp'd me about .25 hours since they wanted me to sit on the tarmac at 1200 RPM until the oil temp gauge came up (something that I would have done anyway).

I made the decision to go, but I also made (a rather poor) decision to board a passenger while the aircraft was running (at the direction of the FBO and because I was at an unattended airport to pick that passenger up). I don't regret taking the aircraft but I never felt comfortable boarding somebody with the engine running.

In this situation you probably would have been fine had you left, provided you were making a VFR flight in good conditions. If this were IFR I would say that it would be better to say "no-go". The only thing you would probably have noticed would have been the ammeter showing the battery charging, but it would probably have recharged the battery in about 30-45 minutes of flying.

The other question is if the owner should have comp'd you for this and that is a little harder. You probably didn't burn all that much fuel or put much time on the engine tach so I'm guessing that while it would have been inconvenient to the owner, you didn't make a lot of difference financially (maybe $20 at most).

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    $\begingroup$ +1 for "As PIC/pilot you have not only the ability, but the duty to call off any flight you don't feel comfortable regardless of the reason" alone. It'd be crazy IMO if the person actually piloting the plane (and thus in charge of their life, and their passengers' lives) didn't have last call on whether to take a metal tube, with some wings and engines strapped to it, up into the sky hundreds/thousands of feet above the Earth. $\endgroup$
    – BruceWayne
    Jan 30, 2018 at 15:54
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    $\begingroup$ What @BruceWayne said. $\endgroup$
    – John R. Strohm
    Jan 30, 2018 at 22:11
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    $\begingroup$ Since no one seemed to diagnose the actual problem—alternator, charging system, or battery—the wisest course is a no-go. If the battery has expired, no amount of engine running will charge it. Also, it could destroy the alternator if the battery's failure mode included an internal short. This sets up a potential chain of failure where the avionics, lights, and electric flaps are inoperable. Night? Short runway? No way to broadcast MayDay? (Bold pilots don't become old pilots.) $\endgroup$
    – wallyk
    Feb 1, 2018 at 8:27
  • $\begingroup$ I'm impressed you got comp'd. I've made it all the way to runup to find the carb heat was bad (arm snapped off) and didn't even get comp'd! $\endgroup$
    – Brian Knoblauch
    Feb 1, 2018 at 17:48
  • $\begingroup$ @BrianKnoblauch Another contributing factor is that I called the FBO for a preheat and they did not do that, they forgot then told me to just "run it", which killed the battery when I tried to start. I knew it wasn't going to start, it was around 20°F outside. $\endgroup$
    – Ron Beyer
    Feb 1, 2018 at 19:31
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Before I answer its pertinent to clarify something as your wording it a bit tricky,

I know that the plane is powered by the magnetos once started

The spark plugs are driven by the magnetos, the airplane (electronics etc) is powered by the alternator/battery once started. This is important as you can have a running engine with both a faulty battery and a faulty alternator. Its also worth noting that in the event of a battery too weak to crank the engine you can even hand prop the aircraft to get it running which, once running (provided there is some juice to run the alternator fields) will recharge the battery.

On to the topic at hand;

As I continued to crank the engine over, you could tell the cranking lulled and the battery was having difficulty turning the engine over as effortlessly as it typically would.

This makes it sound like you killed the battery (or at least it was on its way to dead). A battery's ability to crank an aircraft, diminishes as you use up the stored energy. In your case, if the plane was started and running, while the ammeter was registering 0 or +amp current, then you are good to fly. However, it may be a good idea to idle on the ground a bit and recharge the battery some prior to takeoff to avoid high alternator draw on takeoff and climb out.

If the battery was good for "a series of crank/rest periods" than I would not consider it weak and unreliable.

NOTE: If you are concerned or feel uncomfortable you should never make a flight and you should report any and all things to the owner of the aircraft.

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    $\begingroup$ Couple of nits to pick: "The spark plugs are driven by the magnetos once started". The spark plugs are always driven by the magnetos and the magnetos are driven by the rotation of the engine. "Its also worth noting that in the event of a dead battery you can even hand prop the aircraft to get it running which, once running will recharge the battery." This may work if the battery is too weak to crank the engine, but not if the battery is totally dead. The alternator requires some voltage to set up the field and output power. $\endgroup$
    – Brian
    Jan 30, 2018 at 19:11
  • $\begingroup$ @Brian I have edited the verbiage on the magnetos and alternator to reflect. $\endgroup$
    – Dave
    Jan 30, 2018 at 19:25
  • $\begingroup$ @Brian, is the charging system different from a car? A car can certainly charge a completely dead battery after a push start. $\endgroup$
    – prl
    Jan 31, 2018 at 18:27
  • $\begingroup$ @prl There's won't start the car discharged (usually around 80%) and completely discharged (aka "deeply discharged"). Most times the car battery doesn't get to the second state, because most people know to stop discharging it as soon as it won't start the car. But if you sit there cranking on the starter even after you clearly have a discharged batter, you can really mess it up. $\endgroup$
    – user3067860
    Jan 31, 2018 at 20:39
  • $\begingroup$ You can't push start cars anymore on dead batteries because they have too many electrical loads required to work fuel and spark. When the battery is too low to safely crank, the starter solenoid will drop out and disconnect the starter. At best you will get many clicks, but not for much longer. $\endgroup$
    – Harper - Reinstate Monica
    Jan 22, 2019 at 21:34
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is my decision to not fly unfounded or would there be good reason not to fly knowing that the battery was weak and unreliable?

A weak battery does not generally pose a problem to an electrical system - even if it presents a constant load, the alternator should be more than powerful enough to maintain that load as well as all other electrical loads.

The problem with a weak battery is that it may be a symptom of a more significant problem. If it suggests a failing alternator, bad voltage regulator, or some other issue then it's possible you may experience a mid flight electrical failure.

If it's simply an older battery, it's cold, or it was recently started and stopped without allowing the battery to fully recover from the starting procedure then there may not be any reason to abort the flight as these issues are temporary in nature and do not reflect poorly on the safety of the plane.

However, if the battery failure is due to some other electrical system problem that could disable the electrical system during flight then you have two issues depending on the engine type:

Magneto engine with no engine computer or fuel injection

If the engine does not use fuel injection or an engine computer, and has magneto(s) for spark then it will remain running even without the alternator or electrical system.

In this case, you may lose some or all of your electronic avionics if the electrical system fails. However you should still be able to maintain control of the plane.

Engine with computer, fuel injection, or electronic ignition

If the engine has a computer, has fuel injection, or uses an electronic ignition system (ie, non magneto), then it's possible you'll lose engine power if the electrical system fails.

In other words, if the engine requires power to correctly operate or you require power to correctly fly (for instance needing electronic instruments for IFR conditions) then you should be very careful about flying a plane which is showing any problem with the electrical system.

Understand your electrical system and how to deal with emergencies

You need to understand at least in a basic manner how your plane is wired, and how to operate the breakers correctly in case of electrical failure. You need to understand what redundancy is available in the electrical system, and how to verify that all redundant options are correctly operating.

It may well be that this has already been drilled into you through training on this model of aircraft - when X happens, do Y - but a deeper understanding of the reasons behind taking certain actions when certain alerts occur will help you understand if a weak battery is cause for concern. If your engine has two alternators, if your avionics have multiple battery backups, if you have two power buses and two batteries - all these things can provide confidence that the aircraft will operate well despite having difficulty starting. If the aircraft has none of these, or if you aren't sure, or you don't know how to test or check these systems, then you should probably avoid flight until you've corrected the issue, or learned more about the aircraft.

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  • $\begingroup$ +1 for detailing the actual risks of overall failure. I'm amazed none of the other answers bothered to try. $\endgroup$
    – jpmc26
    Jan 31, 2018 at 1:20
  • $\begingroup$ One caveat: VFR with no electrics is OK, but I would really not want to be IFR without an electrical system, especially on a plane with a glass cockpit! $\endgroup$
    – UnrecognizedFallingObject
    Jan 31, 2018 at 2:50
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    $\begingroup$ @UnrecognizedFallingObject Modern glass cockpits have multiple power buses and multiple power backups so the reality is that even if one bus completely fails you'll still have critical avionics. That said, if you're asking questions like, "Does a weak battery constitute reason to scrub a flight?" then you likely don't know the plane well enough to understand what level of redundancy it has, and how to verify that all the parts of the redundant systems are operating correctly. $\endgroup$
    – Adam Davis
    Jan 31, 2018 at 12:58
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    $\begingroup$ @WayneWerner Yes, in fact they're trained not to think about the problem, but to simply act according to the emergency training and procedures. Thinking not only slows things down, but introduces possible mistakes, and in the air or in space you generally don't have time to figure out the root cause. This isn't unusual to these two areas either, emergency medical technicians have a similar approach. $\endgroup$
    – Adam Davis
    Feb 1, 2018 at 14:27
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    $\begingroup$ That's kind of interesting - I hadn't put 2 and 2 together there, but it makes sense. It also makes sense on a more personal level - talking about needles and blood and cuts gives me the absolute weebles. However, over the year my children have had fairly intensive injuries - cut eyebrow falling off a bike, another bit his tongue, another got some adult-level scissors at a birthday party and cut her hand enough to require stitches. Each time I simply acted according to the Scout and Red Cross training I'd been given - not a single weeble experienced. $\endgroup$
    – Wayne Werner
    Feb 1, 2018 at 14:43
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Dead battery = no go for me. Even if the battery is good, if the engine is hard to crank and not just cold, what if the engine stops in flight and is hard to restart?

I aborted a cross-country vacation in a rented 152 once because of a dead battery one leg into the vacation, went back, and spent a bummer Christmas at home, a decision I don't regret. (What I do regret is trying a "special VFR" approach to SJC on the way back and learning that 1 mile visibility isn't much visibility. Let's just say it was Christmas Day and SJC tower was very forgiving after I overshot the runway at 500 feet after getting clearance to land.)

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If you're unsure of safety for any reason, "no-go" is generally the right choice. If it turns out later you didn't need to be so conservative, that's fine and you can always do it differently next time - what matters is your assessment of the situation at the time. Of course, you are correct that the magnetos will keep the engine running no matter what happens with the rest of the electrical system. The question is what's going to happen there, and how much it matters.

I would have no reservations at all making a "go" decision here for a VFR flight (or an IFR flight in VFR conditions), which I have done uneventfully three times. I would only go if there's a jump available, though - hand propping is definitely a no go for me!

IFR is a little different. It's not an absolute no-go (fully-charged battery is not on the list of required IFR equipment!) If the weather is below VFR minimums, you have a slightly larger (though still small) chance of needing to navigate in IMC without your electronics and having to do lost-comm procedures. If that's not OK, stay on the ground in IMC. For me, this would depend on exactly the situation with the weather. I might also want extra fuel reserves. But this would probably push me into "no-go" territory only if the flight was pretty marginal to begin with.

The power for the electrical system is primarily provided by the alternator. The purpose of the battery is to supply power for starting and to smooth out electrical current - its ability to power instruments is secondary. Once you eventually get the engine started somehow, your battery should recharge fairly quickly IF the alternator is working. Check your ammeter - if the ammeter shows negative or zero charge, you're likely to have an electrical failure and should not fly unless you are prepared to have no electronics for most of the flight. Dead alternators are a common cause of dead batteries, so don't forget to check this!

But if the ammeter shows a positive charge, you're very likely to be fine because the alternator, not the battery, is the important piece of this puzzle. If you have a glass panel or an electronically controlled engine, there's a decent chance you have a dual electrical system to go with it - in that case, you're in better shape with a dead battery than you would be with one alternator and a brand new battery, and nobody would think twice about that!

The bottom line is that electrical systems do fail, and a discharged (but working) battery doesn't really increase the chance of this happening. At most, it reduces the time you have from alternator failure to loss of electrical power. But this doesn't matter as much as you might think it does. Three of the four electrical system failures I've had, counting both aircraft and cars, caught me completely by surprise. One was a dead alternator that I simply didn't notice (did you know a discharging battery is only about a needle's width on the ammeter different from a fully charged one? You will only even notice it if you are pretty familiar with the plane and look closely), another was a dead alternator in a car that didn't have an ammeter, and the third was a wiring failure that happened so suddenly that I couldn't have done anything about it anyway. Only one of the four did I spot before it became a problem by using the instrument cluster.

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  • $\begingroup$ Every car I've had (which, admittedly, isn't that many) has had an indicator light for "generator failure". You don't really need an ammeter (though it might be nice to have), all you need is to know whether there's a drain on the battery during normal operations. $\endgroup$
    – user
    Jan 31, 2018 at 13:15
  • $\begingroup$ Oh, it had the light. If only it had another light, to indicate the failure of the alternator failure light! :) $\endgroup$
    – fluffysheap
    Jan 31, 2018 at 13:17
  • $\begingroup$ "If only it had another light, to indicate the failure of the alternator failure light!" Most cars do. In fact, most any modern car has the same way to test the indicator lights. From engine-off, turn the key fully to the "driving"/engine-on position but don't engage the starter. I haven't seen a car where that didn't cause all of the dashboard indicator lights to turn on; that'll give you a pretty good hint if an indicator light isn't working. Please tell me you follow the manufacturer's (or, in applicable cases, operator's) predrive checklist before pushback or departure. $\endgroup$
    – user
    Jan 31, 2018 at 13:21
  • $\begingroup$ Yeah. The light came on when you turned the key. It just didn't come on when the alternator died. $\endgroup$
    – fluffysheap
    Jan 31, 2018 at 13:27
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    $\begingroup$ @fluffysheap: At least in some automobiles, the alternator light bulb used to be a key part of the alternator circuit, such that a burned out bulb would cause the alternator to stop working; of course, the burned light bulb wouldn't light up to indicate that failure mode, so checking that the light illuminates when the engine isn't running would be important before setting out on a long trip. $\endgroup$
    – supercat
    Feb 1, 2018 at 17:23
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First, don't go if you aren't prepared and comfortable with all aspects of the flight, so from that aspect you made a great decision. As you seem to already understand, the financial aspect shouldn't make even a small difference when it comes to making these decisions.

That being said, the main thing to consider is what happens if the alternator fails and the battery dies shortly thereafter: if the battery is weak, the margin of safety is reduced and this scenario is more likely than normal to develop, but by no means certain. Even if it does happen, the POH will have abnormal and/or emergency procedures to follow.

Some things to consider when contemplating whether it is possible to safely fly in this scenario are whether you are:

  • flying an aircraft that doesn't rely on electricity for critical systems
  • flying in an area that requires certain surveillance or communication equipment (like a transponder or two-way communication)
  • flying under VFR (IFR requires equipment that could quit working)
  • are comfortable flying without electronic navigation assistance and communication radios (or have portable equipment that doesn't require ship power)
  • are comfortable with the additional risk that would be added on to everything else for the proposed flight

Consider the fact that some older airplanes don't even have an electrical system outside of the engine, and they fly just fine! Again though, you need to be comfortable navigating using dead reckoning and without communication equipment if needed.

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