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Like many people, I often either ignore or reset warning lights in my car and continue to drive without issue for months or years (usually due to dodgy sensors giving a false-positive).

What warning lights can we still complete a flight with in small aircraft (Piper Tomahawk, Ikarus C42, Cessna 150s and such)?

For reference, I have read on other discussion forums that C150s often have the low voltage & low oil pressure issues. People have ignored them and crashed... I don't want that to happen.

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    $\begingroup$ For warning lights in a car: don't just assume the light is due to a faulty sensor, but check if this is true. If it is, AND the light does not warn for a critical item, you could consider to keep driving. But be aware you've just reduced your margin for error: you've lost whatever function the light was supposed to warn you about. $\endgroup$ – Hobbes Feb 14 at 11:11
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    $\begingroup$ @Hobbes Or, at the very least, you've lost the ability to notice a real problem with whatever function the light is supposed to warn you about in advance of actually needing that function. $\endgroup$ – a CVn Feb 14 at 12:02
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    $\begingroup$ Ignore or reset the warning lights in a car? You mean the ones that tell you there's a flat tire, or you're low on oil and your engine could seize up, or your brakes are about to stop working? Even if it's a non-safety related sensor failure chances are your performance or mileage will suffer, or cause long term damage which will be more expensive later. Don't ignore them in a car, and certainly not an airplane. $\endgroup$ – GdD Feb 14 at 13:59
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    $\begingroup$ @cloud: Because it's a terrible idea to ignore warnings in an aircraft. $\endgroup$ – Hobbes Feb 14 at 16:00
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    $\begingroup$ Next time you get crud kicked up on your windshield on a crowded highway at night and can't see out the answer is likely yes @abelenky. $\endgroup$ – GdD Feb 14 at 16:05
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In general, the procedure will be to exercise good pilot judgement. In many cases, this will include or begin with pulling out the checklist and/or performing memory items from the checklist.

Small airplanes don't have the huge array of sensors that airliners are equipped with. Especially in an ultralight like the C42, you might be lucky to have a few engine instruments and a master caution/warning light.

For example, in the C42 that I fly, the typical reason for the master problem (really, a combined master caution and master warning) light to come on in flight is that the cylinder head temperature is too high, in which case in that airplane the appropriate action is to fully open the cowl flap and to reduce power but generally to maintain speed, to allow the engine to cool down in a quick but controlled manner allowing continued flight; then adjust the cowl flap for the current flight regime. The way to verify that this is actually the problem is to look over at the CHT gauge and see if it's above the green arc. However, if it's not the CHT, that same light might come on for, say, an electrical problem, which would call for an entirely different set of actions in response and might require landing soon, before the battery is depleted.

The lights only really serve to direct the pilot's attention to the fact that there is a problem.

I agree with Sanchises' point to never ignore warning lights, or for that matter other indications of problems, in an aircraft. Heck, I don't ignore warning lights even in my car, let alone in an airplane. (I don't know how many times I've told my instructor something along the lines of "it wants attention" as I started to scan the instruments specifically to see what problem caused the problem light to come on.) That doesn't mean that the appropriate response for every problem is to land immediately.

On the flip side, in extreme situations, it might be appropriate to continue flying even with something like a low oil pressure indication, which if determined to be accurate (which you can't always rely on, and certainly can't assume; it's the old adage, trust but verify) would normally call for an engine shutdown and engine-off landing. To keep flying with low oil pressure will quite possibly ruin the engine, but if the alternative is a crash landing or a ditching over open water, then it comes down to that rebuilding or replacing the engine is likely to be cheaper than would be replacing the entire airplane. Either way, though, in such a situation you make an informed, conscious decision on which action to take in response to the problem. Following the prepared checklist for diagnosing and dealing with the problem in that particular airplane should be the first step in that process.

Expect great fun when you're just entering the downwind leg for landing, or are at low altitude and near the end of the runway during climb-out, or over the woods, or some similarly precarious situation, and the instructor tells you "we have an engine fire, now what do you do?".

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  • $\begingroup$ Thanks for all the advice. I've actually seen videos of instructors reducing to idle at low altitude shortly after takeoff to simulate engine failure. I'm not looking forward to that. $\endgroup$ – Cloud Feb 14 at 12:02
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    $\begingroup$ @Cloud Properly maintained airplane engines are actually supremely reliable devices. The one exception to this is in the case when a certified flight instructor or flight examiner is sitting in the next seat over, at which point they tend to develop problems every few minutes or at least once or twice per flight. You get used to it. Just don't grow to rely too much on the engine magically restarting. $\endgroup$ – a CVn Feb 14 at 12:16
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The items that need to be operational for an aircraft to be considered airworthy are laid out in the Minimum Equipment List (MEL).

In-flight, follow the appropriate checklist for the warning light. Typically, it calls for troubleshooting the problem, and if the problem persists, directions on how to continue. Options typically range from "continue flying" (for example, vacuum failure could allow for partial panel procedures), "land as soon as safely possible" to "initiate forced landing" (engine fire).

As a general point of principle, don't ignore warning lights in aircraft. If it wasn't a problem, it wouldn't have a warning light.

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  • $\begingroup$ This applies before departure. But I am also considering scenarios where you are in the air and a light comes on. At this point, you need to decide whether to continue or turn back I suppose. $\endgroup$ – Cloud Feb 14 at 10:31
  • $\begingroup$ @Cloud In-flight, always follow the appropriate checklist. $\endgroup$ – Sanchises Feb 14 at 10:57
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Looking at your typical Cessna 172 there will be perhaps 2 warning lights:

  1. After start warning light: this tells you the starter motor has not disengaged. If you ignore it you can cause serious damage to the engine. Stop your engine immediately using a lean cut-off and terminate the flight, informing maintenance
  2. Low alternator voltage: this tells you the ammeter is not showing a positive battery charge. If the battery isn't charging then your battery will die and you'll lose all your electronic instruments and avionics, including transponder and radio. Try cycling the alternator side of the master switch off and back on and see if it starts charging. If the light goes away then keep an eye on it and get it looked at by a mechanic, if the light stays on turn off all non-essential instruments and avionics to preserve your charge and divert if you aren't close to your destination. Inform ATC

Don't ignore warning lights.

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  • $\begingroup$ As I recall, the 172s I flew also had low vacuum warning lights in addition to the lights you mentioned. $\endgroup$ – Fred Larson Feb 14 at 20:47

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