Are fuel gauges considered engine instruments?

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goinaround
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Are fuel gauges considered engine instruments?

Post by goinaround »

I have a question.

Are fuel gauges considered engine instruments?
Or are engine instruments things like oil pressure, oil temp, torque, ITT, and Ng?
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nine sixteenths
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Re: Are fuel gauges considered engine instruments?

Post by nine sixteenths »

goinaround wrote: Mon Apr 15, 2024 5:56 am I have a question.

Are fuel gauges considered engine instruments?
Or are engine instruments things like oil pressure, oil temp, torque, ITT, and Ng?
Fuel quantity gauges, no, not engine instruments. Fuel Flow gauges, yes, engine instruments.

In terms of technical logs for your aircraft per CAR 605.92, neither are an engine instrument, both are an element of the airframe
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PilotDAR
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Re: Are fuel gauges considered engine instruments?

Post by PilotDAR »

Consider if the instrument is required so that you may abide by a limitation, if so, would that be an engine limitation, or an airframe limitation? Or, unrelated to those, an airspace or operational limitation. Or, it could be specified on an engine or airframe type certificate data sheet as being required.

So, no, a fuel quantity gauge would not be considered an engine instrument. But in terms of having to have them working, operational requirement for fuel planning enroute.
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goinaround
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Re: Are fuel gauges considered engine instruments?

Post by goinaround »

I completely agree. Fuel gauges do not tell you anything about the health of the engine. They tell you how much fuel you have...kind of. So when a checklist calls for a engine instruments check one would naturally look at the toque, ITT, Ng, Oil temp, oil pressure as those as those 'engine' instruments would tell you the current state/health of the engine.
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Big Pistons Forever
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Re: Are fuel gauges considered engine instruments?

Post by Big Pistons Forever »

Fuel guages are also required instruments per CAR 523.2430. The aircraft is not airworthy if the fuel gauges don't work. Some engines gauges may be required or not depending on the type certificatge requirements, equipmenmt list, or MEL.
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CaptDukeNukem
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Re: Are fuel gauges considered engine instruments?

Post by CaptDukeNukem »

You’re kidding right? Apart from not checking the fuel level in my lawn mower, I would probably like to know how much fuel is in any machine before I go operate it.

Yes, it’s a CARs requirement, as is a compass…, and a time piece lol.
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Re: Are fuel gauges considered engine instruments?

Post by PilotDAR »

I also like to know how much fuel I have for the intended operation. It is unlikely that I will use a fuel gauge to make that determination, unless I have no other means. I just don't trust them that much, when dipping is easy. Unlike other airplane parameters, the total fuel aboard will only go down after takeoff. Other than monitoring the transfer of fuel, I'm happier with time, and fuel flow to be more certain of the amount of fuel I'm carrying - I have been let down by fuel quantity indications too many times.

That's not to make a statement one way or the other about the legal requirement for fuel quantity indicators to be functional, but fuel transferring aside, you're not going to exceed a fuel limitation because a fuel quantity indicator was not working during flight!
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Big Pistons Forever
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Re: Are fuel gauges considered engine instruments?

Post by Big Pistons Forever »

I am personally mystified why some many pilots accept US fuel gauges as acceptable. I compare what the guages say vs what the dipsticks or fuel slip say. You will pretty quickly get a feel for how accurate the gauges are. My personal experience with light aircraft fuel gauges is that if they are working properly they are quite accurate in the lower third of their travel, so I will pay attention to low fuel gauge indications. Yes you obviously should know what you have onboard before takeoff and do the math for expected fuel burn but working gauges will give you warnings of a fuel leak or unexpectedly high fuel flow.

I have personally had an engine failure that was directly caused by the malfunctioning guages the owner didn’t mention. The gauges sort of matched the fuel load when I looked in the tanks but it turned out the fuel selector failed and the airplane kept on drawing on the aux tank even though I had selected main. Since the aux gauges were not working there was no indication that the aux tank was empty, or was it obvious that the main quantity hadn’t changed. One engine failed half way down the glide slope for the ILS on a 500 and 2 day.
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Last edited by Big Pistons Forever on Sat Aug 17, 2024 2:32 pm, edited 1 time in total.
DanWEC
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Re: Are fuel gauges considered engine instruments?

Post by DanWEC »

Strictly speaking, I don't believe gauges are actually required unless it's part of the original equip. I believe it's only a requirement to be able to obtain the amount of FOB. At it's simplest that's just a dippable tank design. Just look at how useless the gauges on a 172 are.
Also, a sight glass as in the cub I used to fly is perfectly acceptable and a lot more accurate.

PilotDAR, you just posted as I was writing this, do you know if a type can be certified without a way to obtain fuel level in-flight?

Is it an engine instrument? That's debatable. It certainly isn't an engine performance indicator, but it is something you'd immediately scan at the first sign of an engine issue. But so would a carb inlet temp gauge if so equipped.
It's an "engine related" instrument, and any more dissection is just semantics, and wouldn't really have any relevance except for discussing a multiple choice exam question- which I bet is why this question is here. ;)
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Re: Are fuel gauges considered engine instruments?

Post by digits_ »

PilotDAR wrote: Sat Aug 17, 2024 1:56 pm That's not to make a statement one way or the other about the legal requirement for fuel quantity indicators to be functional, but fuel transferring aside, you're not going to exceed a fuel limitation because a fuel quantity indicator was not working during flight!
Hmm by that logic, in a small plane you don't need a fuel flow, oil temperature or oil pressure gauge either. You're not going to exceed any limitations when they aren't working either...

Even an RPM indicator won't be needed, once your max rpm has been set by your AME...

All these gauges, if properly working, will alert you to problems. A fuel gauge isn't special in that regard, other than that for some reason we sort of assume they don't work accurately anyway. We would never accept an oil pressure gauge that's 50% off, but for fuel gauges in light aircraft we're all ok with it (me included by the way, I'm just as guilty). A very curious insight into the human psyche :o
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Re: Are fuel gauges considered engine instruments?

Post by PilotDAR »

oil temperature or oil pressure gauge either. You're not going to exceed any limitations when they aren't working either...
Sure you could, oil temperature could slowly or suddenly rise, or pressure drop. I wold sure like to know that in real time, especially to see a bad trend starting. Depending upon the type of prop, it may be difficult to exceed RPM limits in "normal" flight (it's something I have to check for by flight test for some propeller change approvals). But, if a governor goes bad, you can exceed RPM limits with a CS prop. 'Had it happen once in a C 340.

The engine instruments are required to assure that an engine operating limitation is not exceeded. Fuel quantity is not a limitation, as long as you have enough!
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CaptDukeNukem
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Re: Are fuel gauges considered engine instruments?

Post by CaptDukeNukem »

Okay. So you start by dipping the tanks… enough fuel for the flight. Awesome, let’s go.

Then a fuel leak develops, but you don’t have a working gauge to compare it to anything such as your navlog? You guys are mental flying planes with no way to check fuel on board in flight.
I’d rather be relatively close with mediocre fuel estimations then to just press on and hope all is well. I’d suggest you guys go work for keystone airlines if they were still in operation. They would take you in a heartbeat
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Re: Are fuel gauges considered engine instruments?

Post by PilotDAR »

Oh I'm not advocating flying with U/S fuel gauges, I'm just saying to think about their importance in a different way than an instrument which is required to assure an engine limitation is respected. Twice, a good fuel quantity indicator has shown me a fuel loss in flight, which caused me to change my planning, and many times, an engine instruments headed toward a limitation has similarly caused me to reduce my expectations of power available. Everything should work, but when it quits, you should understand what you were depending upon it for in the first place!
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