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Why don't small airplanes (like Cessna or Cirrus) have "Check Engine" lights, like cars do? For the most part, the people flying these airplanes don't know much more about the plane than they do their car. Wouldn't a "Check Engine" light be useful to many people flying these planes?

Or do the rigorous maintenance schedules required for airplanes invalidate any use that a "Check Engine" light would have?

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    $\begingroup$ Don't forget you have manifold pressure, cylinder head temperature, exhaust gas temperature, oil pressure and oil temperature gauges in an airplane while you don't have either in a car. $\endgroup$ – Jan Hudec Nov 3 '14 at 6:15
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    $\begingroup$ I'm not a pilot, but I suspect "just knowing something is wrong" isn't going to be useful. With a car, you pull into a mechnanic, or off to the side and call AAA. With a plane you need to know what is wrong now because there is no one look at it until you get on the ground, which you might not be able to do. No one, that is, except Tom Cruise. $\endgroup$ – corsiKa Nov 3 '14 at 17:01
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    $\begingroup$ aren't check engine lights for ignoring for the next 15,000 miles and saying "I've been meaning to check that out" whenever a passenger brings it up? Probably I'm just a poor caretaker of my car. $\endgroup$ – coburne Nov 4 '14 at 15:06
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    $\begingroup$ Obligatory Big Bang Theory reference $\endgroup$ – RedGrittyBrick Nov 5 '14 at 15:24
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    $\begingroup$ @kjmccarx so was I - "Light's out! NO PROBLEM!" (much easier to just reset the thing than the alternate-but-permanent solution of climbing behind the dash and unplugging the lamp!) $\endgroup$ – voretaq7 Nov 6 '14 at 20:15
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With a few exceptions (modern aircraft engines with FADEC systems) a "Check Engine" light on an aircraft would be essentially useless.

In a modern car we have an Engine Control Unit which manages things like mixture and engine timing. The "Check Engine" lamp illuminates when the ECU has detected a fault that requires some sort of attention, but it's not usually specific as to what the fault is or how urgent the problem is.

In most light GA aircraft (like the Cessna or Cirrus in your question) the engines are straight out of the 1950s/1960s: There are no computers managing the engine for you, and the pilot is acting as the ECU.
The pilot should be checking the engine's health regularly (by looking at the engine gauges) and adjusting power, mixture, and propeller pitch as required.

Since there is no computer supervising the operation of the engine in most light GA aircraft there's no system to determine when the light should be on, so there is no "Check Engine" light.


Note that some light aircraft do incorporate warning lights for system status information. For example, the status cluster on newer Piper Warriors:
Warrior III warning lights
Top row: Low bus voltage, Pitot Heat off/inop, starter engaged.
Middle row: Vacuum inop, Alternator inop, Oil Pressure.
Bottom row: Not used on this aircraft.

The information provided by these lights is more specific than simply "Check Engine" - directing the pilot's attention to a specific system or condition. The lights are also not a substitute for regularly scanning the engine instruments and managing the powerplant, they're merely a supplement to catch your attention between scans.

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    $\begingroup$ I think this answer deserves more upvotes. The Cessna 172R--the first with fuel injection--wasn't released until 1996, if Wikipedia is telling the truth. In most 152s and 172s I've been in, the instrument panels are ancient. Age is the simple explanation here. $\endgroup$ – D__ Nov 3 '14 at 20:15
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    $\begingroup$ This. The engine I fly most is an O-320, first flown in 1953 and preeeetty much not modernized since. $\endgroup$ – egid Nov 3 '14 at 21:45
  • $\begingroup$ +1 for mentioning an annunciator panel. I didn't even think about that. $\endgroup$ – Keegan Nov 4 '14 at 0:29
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    $\begingroup$ If I owned that Piper Warrior, I would forever regret not buying the model where all of the rows were used. Like when you buy a cheap car, and you can see the spot where the button would be, if only you weren't such a cheapskate. $\endgroup$ – Mark Henderson Nov 5 '14 at 2:58
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    $\begingroup$ i think its also worth mentioning that planes with a large number of annunciators also have a "master warning" and "master caution" lights in the center of the panel, which, like the "check engine" light have the purpose of drawing the operator's attention to a problem, without stating what the problem is. $\endgroup$ – rbp Jan 31 '16 at 15:34
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Because your basic premise is completely wrong. The people flying a Cessna or Cirrus generally have a vast amount more knowledge about their planes than the average car owner. Between the POH (Pilot Operating Handbook) and the general systems information that is part of every level of curriculum that level of knowledge of your average GA pilot is vastly greater than your average driver.

Add to it that indications need to be specific in airplanes. A pilot needs to know what failed in and what way so they can make an appropriate decision. Their lives depend on it, unlike in a car.

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    $\begingroup$ You say my premise is wrong, but I know the inside of my Jeep's engine better than I know the inside the engine of any of the airplanes I fly. Sure, I know exactly what to do if my airplane engine fails, by no means does it mean that I have more knowledge of the ( specific engines from the) planes I fly than the cars I drive. $\endgroup$ – Keegan Nov 3 '14 at 5:07
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    $\begingroup$ @kjmccarx And you apparently know far more about your Jeep then the "average driver" that John referred to. Most people are completely oblivious to what makes their car work, whereas the average pilot does know more about the systems than the average driver. $\endgroup$ – Lnafziger Nov 3 '14 at 5:54
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First, consider what a check engine light actually tells you. In short, it could be almost anything, which isn't very useful information. To find out what the specific problem is, you need to go to a garage and have a mechanic run a diagnostic check to determine what triggered the light.

In a car, that's no big deal, but in an aircraft that's a huge problem: imagine that you're flying above cloud at night with potential icing below you and the light comes on (for this discussion, let's leave aside the wisdom of putting yourself in that position in the first place). In the absence of other information, what action do you take? Is it serious enough that you need to get on the ground ASAP and risk the descent through freezing conditions? Or is it reasonable to continue to your destination? Or compromise and look for an alternate that's clear of cloud but not on the way to your destination? The only way to make an informed decision is to have as much specific information as possible, and a single 'something's wrong' light doesn't give you that.

Second, I don't know if your question is deliberately provocative but I question the assumption that light aircraft pilots don't know much about their aircraft systems. Your profile says that you hold a private pilot's license and are in the USA, and the USA FAA's Practical Test Standards require the following:

Task G: Operation of Systems (ASEL and ASES)

References: FAA-H-8083-23, FAA-H-8083-25; POH/AFM.

Objective: To determine that the applicant exhibits satisfactory knowledge of the elements related to the operation of systems on the airplane provided for the flight test by explaining at least three of the following systems:

  1. Primary flight controls and trim.
  2. Flaps, leading edge devices, and spoilers.
  3. Water rudders (ASES).
  4. Powerplant and propeller.
  5. Landing gear.
  6. Fuel, oil, and hydraulic.
  7. Electrical.
  8. Avionics.
  9. Pitot-static, vacuum/pressure and associated flight instruments.
  10. Environmental.
  11. Deicing and anti-icing.

Of course some pilots will cram for their test and then forget a lot of this information, but in general I think it's pretty difficult to get a pilot's license without having a good working knowledge of aircraft systems. Speaking personally, I know a whole lot more about the systems in the aircraft that I fly than I do about the ones in the car I drive (in part because the equivalent instrumentation and information simply aren't available to me in the car).

Finally, maintenance is essential but by itself it doesn't reduce the need for the pilot to understand what's going on. It's commonly said by pilots that it's important to fly the aircraft conservatively for the first few hours after a major service and if you do have some kind of failure in that time then you should suspect it's related to the maintenance. Maintenance can only reduce failures, not prevent them completely, and when something does go wrong then you still need as much information as possible.

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    $\begingroup$ Exactly. Just about every pilot I know has participated in the annual inspection of their airplane. I’ve done at least 30. I know where every pulley and turnbuckle is. I look at the alternator belt, brake fluid, spark plug wires, tires, and brakes before every flight. And we have oil temperature and pressure gauges, exhaust gas and cylinder temperature gauges, and fuel totalizers to monitor in flight. I know a whole lot more about my airplanes health than I do about the cars I drive. $\endgroup$ – JScarry Feb 5 '17 at 2:06
  • $\begingroup$ > First, consider what a check engine light actually tells you. - it tells you precisely what a Master Warning light does, and for the same reason. SOMETHING is wrong, go find it. I'm surprised people are suggesting this isn't a good idea, considering most aircraft (and spacecraft) have one! $\endgroup$ – Maury Markowitz May 25 '18 at 15:46
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Generally, the vigorous maintenance and checks on aircraft mean that a light is superfluous - you'll have checked things fairly recently anyway.

And if you're already in the air and your engine develops a problem, you likely don't need a light to inform you....nor would one particularly help you out, unless the bulb is particularly good at engine-out landings.

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    $\begingroup$ I lol'd at "unless the bulb is particularly good at...landings". $\endgroup$ – cHao Nov 3 '14 at 17:47
  • $\begingroup$ Vigorous maintenance and checks are also performed on cars. On-going maintenance for cars includes oil and filter changes, tire pressure monitoring and replacements, brake and rotor inspections, bulbs and lights plus a number of engine related checks and changing parts. Regardless of age, every car needs maintenance. The difference with airplanes is that cars' maintenance isn't thoroughly regulated as airplanes. $\endgroup$ – Farhan Nov 3 '14 at 20:55
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    $\begingroup$ It isn't as thoroughly regulated, nor is it as thorough in itself, nor as regularly performed. A car is lucky to get the above once a year, and servicing is usually optional, with road fitness tests only catching things that are already broken.... $\endgroup$ – Jon Story Nov 3 '14 at 21:14
  • $\begingroup$ @Farhan Yes, cars need maintenance. However, as Jon said, they don't usually receive maintenance or inspection nearly as often as an aircraft. Several of the aircraft's systems are literally checked before every single flight, even in general aviation, as part of the pre-flight checks. It's not like we take the engine apart or anything, but there is a pretty significant set of systems checks in the pre-flight checklists, even for very basic single-engine land aircraft. $\endgroup$ – reirab Nov 4 '14 at 17:56
  • $\begingroup$ :"vigorous maintenance and checks on aircraft mean that a light is superfluous - you'll have checked things fairly recently anyway." - I think you have replaced effect with cause. The reason we need all those checks is because the engine doesn't do them itself. This is a problem, not a feature. $\endgroup$ – Maury Markowitz May 25 '18 at 15:49
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The reason the "Check Engine" light, called the Malfunction Indicator Lamp (MIL), exists in cars is due to legislation. Road vehicles have strict EPA standards to follow regarding emissions that include not only the exhaust and air/fuel mixture, but the fuel tank evaporation, and crankcase oil ventilation. The only way to meet these standards is by computer control of the engine and other aspects of the vehicle. The light is mandated to indicate when any one of these systems isn't operating within specification, and thus may have higher emissions than what meets the standards.

While drivers think of the light as an early warning indicator for vehicle trouble, the reality is that its primary purpose is to encourage drivers to keep their vehicle within the emissions standards it was originally designed for. These change over the years, newer cars have more strict standards to follow.

Small aircraft follow the non-road emissions standards, similar to construction equipment, lawnmowers, generators, and off-road vehicles. None of these are required to follow such strict standards (though they must meet minimum standards, and these are getting more involved), and the standards they do follow can be done with no computer control. There is no legislation that requires a lamp indicating that the engine is operating at higher emissions than intended.

Larger aircraft have lower emissions because they are required by customers to be very fuel efficient, and one way to increase fuel efficiency is to add computer control that uses as much energy from the fuel as possible, thus burning it more completely. These systems are expensive, though, and only make financial sense if the aircraft is going to be flown many, many hours over its lifetime. They also do follow stricter standards, but the indicator lamps and manufacturer diagnostic equipment are more comprehensive for these aircraft to enable overall cost-savings and increased reliability/safety required for passenger service.

The EPA is due to make recommendations in late 2015 and early 2016 that will affect aircraft emissions. At that point in time it may be that new aircraft will need to be under computer control and will need a check engine lamp.

This might be fundamentally different though. In a road vehicle if there's a problem, you don't need to know what it is to be safe - you can pull over and call a tow truck. Aircraft have no such luxury, so while there may be a lamp indicating excessive emissions, chances are good pilots will still rely on multiple other indicators to determine what malfunction has occurred so they can respond best to the circumstances.

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The "check engine" light on a car is triggered by the on-board diagnostics computer that most every (if not every) car manufactured since 1997 has been required to have (if it is to meet U.S. standards, anyway).

On the other hand, small airplane engines, due to the very conservative nature of aviation, the cost of certification (even just certifying a change to an existing design), and concerns about reliability and redundancy, are almost unchanged since the '50s (no on-board computer, for example). Fuel-injected engines, I believe, are all mechanically operated, rather than electronic like you would have in your car. Without an on-board computer or electronics, there is nothing to trigger the warning lights that we've taken for granted for the last twenty years in our cars*.

*Many small airplane engines do have at least a couple of warning lights, such as low-voltage, low oil pressure, etc., but they are controlled by simple relays rather than by a computer.

Source: I'm a flight instructor, and flew an "amateur-built experimental" airplane for a few years.

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Many planes now are being retrofitted with Engine Monitoring Systems, where many things are presented to the pilot and Warnings are presented when limits are exceeded.

This is a JPI Instruments 6-cylinder presentation, my aircraft has the same unit but is only 4 cylinders. The display is customizable for the probes that are installed. There are other manufacturers for monitor systems as well. Most are a big step up from the simple analog meters originally installed. Datalogging also allows data about flights to be downloaded and discussed with a mechanic for troubleshooting, trend analysis, etc. With Engines costing tens of thousands of dollars to repair, or overhaul, or replace, owners want to keep them running smooth, and get us in the air and back down again safely.

JPI EDM900

Info:

Engine RPM

Engine Manifold pressure (used to set controllable pitch propeller)

% of engine horse power being created

Outside Air Temperature

Exhaust Gas Temperatures/cylinder (used for leaning out the mixture as one climbs)

Cylinder Head Temperatures (used to let you know if a cylinder is running too hot, or colder than the rest, both indicative of a problem)

System voltage

Amperage flow

Oil Pressure

Oil Temperature

Fuel Pressure

Fuel tank levels

Total fuel

Fuel flow (gallons/hr)

Fuel Used

Fuel Remaining

Time to Empty

Carburator Throat Temperature (carburated engine)

Additionally, it can send data to a moving map GPS to show a fuel range circle

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The approach taken in designing aircraft, and certifying their equipment, is to provide for the greatest reliability at the cost of increase pilot workload. The pilot mostly has very little to do for a majority of the flight, being cruise-at-altitude, so it makes sense to require the pilot to scan and interpret simple, reliable indications of current engine status, and draw inferences as to the operational health of the engine as a whole.

For example, the process by which fuel and air is mixed in the carburetor of a non-turbine engine is completely a manually-controlled process. The human is involved as the feedback control element in a closed-loop system, where the mixture control (lean to rich) is the effector, and the RPM and altitude gauges, or the Exhaust Gas Temperature gauge (EGT) are the affectors. The pilot adjusts the mixture to the point which peaks EGT or RPM, and perhaps makes a small adjustment "in the rich direction for cooling", but this is done during climb and descent, as the altitude is changing, and is completely initiated by the pilot (frequently prompted by an item on a climb or cruise flight phase checklist).

Why not delegate this task to an automatic system? Well, first of all, that would provide another point of failure. The EGT and RPM indicators are quite robust and unlikely to fail; likewise with the mixture adjustment knob/lever. The pilot provides the "complex" control system closed-loop control. Imagine if the controller of an automatic system were to fail, and the engine remained in its leanest setting during descent? The system could go into pre-ignition or worse, pre-detonation, leading to a catastrophic failure of the engine! No, the FAA and aircraft builders err on the side of fewer automatic systems in favor of simplicity and reliability.

Someday ask a pilot about all the various things they must tend to, which could be attended to by a modern, computer controlled automatic system. You'll be surprised!

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  • $\begingroup$ We must make light aircraft more idiot-proof, so we can have more idiots flying light aircraft! Oh, wait... :-) $\endgroup$ – Bob Jarvis Nov 4 '14 at 19:09
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Modern aircraft generally have a "master warning" and "master caution" warning lights which direct the pilot to scan the panel to identify the failed system. Master Warnings impact directly on the safety of flight, master cautions are the "need to know about but don't panic yet" systems, eg, an engine fire is a master warning (yes, there's lots of other alarms going off for this as well), but an oil pressure drifting outside of it's normal operating range or a diminishing hydraulic quantity would only trigger the master caution.

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