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G4 Engine Monitor   

Trust your engine to the best technology available today -- G3-G4

Compare both engines on one screen or study them individually for detailed analysis!

G4 Twin

Here's why you should install G4:

Designed For Multi Engine


  • The G4 is designed to handle the special requirements of twin engine aircraft.
  • It is not as simple putting in an instrument for each engine.
  • For example logging data from each engine simultaneously in a single file is crucial because comparison of both is key.
  • Comparison in flight is important too so the G4 can display both engines at once or one at a time for a more detailed view.
  • Of course it is easy to display whatever you want.
  • The G4 also does exhaust valve analysis, fuel flow totalization and horse power calculation for both engines simultaneously.
  • Just like our single engine instruments it provides the very important probe analysis for easy troubleshooting.
  • Nothing comes close to the power, ease or simplicity of the G4 for twins.


G Series is the best technology available, there’s nothing else like it, nothing even comes close. Operation lean of peak requires special information that only the G3 or G4 graphic Engine Monitor can provide. The G Series instruments are extraordinarily capable yet easy to use. G Series specialized innovative leaning process is the first and only one to ever earn a patent, which may be read here.
Unprecedented in its sophistication, most importantly it makes a complex process easy to accomplish. Leaning with reference to temperature only is just too confusing for LOP. Our specialized process reports each individual cylinders status in unambiguous form. You needn’t ponder if a cylinder is rich or lean, the G Series will display that too.

Injector Analysis:

Nozzle flow uniformity is paramount to operation lean of peak but only Insight delivers a nozzle analysis every time you lean.

G Series can forewarn of problems and assure uniformity of results. Of course, other systems just leave you in the dark.

G Series Data:

G Series instruments are not just temperature indicators, they compute real-time results using manifold pressure, RPM, fuel flow and temperatures.

G Series handles the raw data to eliminate confusion and provide answers. It couldn’t be easier.

While constantly displaying critical information during flight the G Series always work diligently behind the scenes too, logging data to a handy SD card for study later so nothing is missed.

It’s easy to go back in time, study trends and trace problems to root cause.


Decades ago Insight introduced the first instrument to display cylinder and exhaust gas temperature of all cylinders simultaneously.

This innovation eventually became the industry standard as all other manufacturers followed suit.

Engine monitors depend on numerous temperature probes that have equal potential to inform or confuse when any of them fail.

In fact probe failures can easily be confused with engine failures.

Only the G Series has a  probe diagnostic system built in.

G4 Twin

Manufacturing G Series at Insight




G4 Size



G4 Twin

G4 Twin

Restarting The Leaning Process

Restart the leaning process and resetting the peak indications on G4 Twin by a short push of the SEL button.
Holding the SEL knob for about 3 seconds on G4 twin R/L screen will take you back to twin-engine screen.



Probe Screen

G4The Need for better Diagnostic Tools

Even the first GEM could detect an open probe and blank its indication. Over the years by helping owners and their mechanics trouble shoot instrument problems I developed a new understanding and sympathy for the challenge they faced.

Troubleshooting avionics is an expensive and time-consuming process. Often times the procedure requires access to the instrument connector for continuity measurements. This might take hours of instrument panel disassembly just to touch the connector. We needed something better, easier to use, less time consuming and therefore less expensive.

Why not have the instrument diagnose itself? Then you don’t have to disassemble the airplane or even touch the wiring. This is not as easy as it might seem. Adding resistance measurement hardware for each and every probe wire would more than double the complexity of the measurement system. I considered this carefully during the development of the GEM-610 second generation instrument. It would at least add a second PC board to the instrument and have even greater adverse impact on the GEMINI twin version. Even if we endured these problems to get the information we had no practical way to display it on an orange bar display.

So I abandoned it then, but revisited again this time. The new color display was certainly adept at displaying the information, eliminating that problem, but the resistance data was still hard to get.

So this time I was able to invent a new way of measuring resistance. The simple idea worked beautifully without adverse impact on the design. It was so simple in fact even I was skeptical at first.

Without this simple breakthrough we’d still be diagnosing things the hard way.

So what does the diagnostic system do?

The probe diagnosis page indications are in green for normal readings and red for readings that fail the criteria set at the bottom of the screen. 

Each temperature probe consists of two wires, a positive lead and a negative lead. The two numbers next to each identifier show the resistance in Ohms of each lead. 

For example, the line EGT1 8 3 means the positive lead of the EGT1 probe has 8 Ohms resistance, and the negative lead has 3 Ohms resistance.

When the probe is new, it will have relatively low resistance. 

As the probe ages, it’s resistance will slowly go up. Eventually, the probe will measure outside the pas/fail criteria you set at the bottom of the screen, and change from green to red, indicating that the probe should be replaced before it fails and leaves you with no temperature reading at all. 



One other point to consider is that the longer the wiring to the probes, the higher its resistance. 

Every foot of EGT wire adds 1.7 Ohms/ft for the + lead and 0.8 Ohms/ft for the - lead. Every foot of CHT wire adds 0.8 Ohms/ft for the + lead and 1.2 Ohms/ft for the - lead. 

A 24 ft harness will fail the criteria that an 8 ft harness will pass with. That is why we allow the user to modify the pass/fail criteria on the bottom of the screen.
The meaning of the pass/fail criteria is as follows:

R MAX sets the maximum resistance (in Ohms) that any single lead may have. If the R MAX is set to 20 Ohms a probe with either the positive or negative leads measuring greater than 20 Ohms will be annunciated in RED, otherwise its displayed in GREEN.

R DIF sets the maximum resistance (in Ohms) that the positive lead may differ from the negative lead. If R DIF is set to 10 Ohms, the positive and negative leads need to measure within 10 Ohms of each other to be annunciated in GREEN, otherwise its RED

EGT Variation Screen - View Mag Ad.

G4This is a new form of engine analysis.

Some valve related engine faults produce a slow periodic variation in EGT.

The oscillation rate is on the order of one cycle every minute or two. This is just too slow to be identified by occasional observation of the temperatures alone. Yet it is very important to discover this phenomenon because it may lead to a catastrophic engine failure. It readily appears in a slow sampled spectrum analysis.

Temperature samples are collected once per second for each cylinder and analyzed each second. The entire sample interval is about 8 minutes. A normal indication will be a flat line with a little noise, while a trouble indication will show as an obvious spectral peak.

Vibration Screen

New Capabilities for the Next Generation G4 GEM

If you take a step back from the EGT/CHT idea to explore engine monitoring in general, you discover that at least half the engine monitoring solution is missing. EGT analysis reveals combustion phenomenon but simply ignores mechanical problems.

By the time a mechanical problem shows up in EGT, if it ever does, the damage is done and it is far too late to do anything about it.

Vibration analysis is the key to pre-emptive detection of mechanical problems.

Following the update of the G4 Graphic Engine Monitor to V1.78 or higher, the Vibration Analysis screen will now appear among the supplementary screens when the PG knob is turned. In order for the vibration analysis to function your G4 must be equipped with a vibration sensor and a connection to the magneto for RPM measurement.  If your instrument was purchased prior to September 2011, Insight will be sending you a vibration sensor shortly.  Instruments purchased after this date will ship with the sensor included with the main kit.

After the electrical connections to the sensor are made, then sensor may be tested simply by powering up the G3 and vibration sensor. It is not necessary to start the engine to perform this test. The sensor LED should flash briefly and rapidly when power is first applied until communication is established with the G3, at which time the LED blinks more slowly (approximately once per second). When the LED indicates communications with the G3 has been established select the Vibration Analysis screen by turning the PG knob. While observing the vibration graph disregard the “RPM Required” message and rap lightly on the vibration sensor with the handle of a screw driver. The graph should register the impacts.

The sensor should then be firmly mounted directly to the engine case, preferably oriented in such a manner as to match the small airplane symbol engraved on the sensor body. In some rare cases it may not be possible to mount it in this manner, and the installer will have to fabricate an appropriate bracket or else be prepared to compensate for the change in orientation when viewing the vibration data. A representative installation is shown in the following figure:



Using the Vibration Analysis Screen on the G4:

The sensor detects vibration in all 3 axis (fore-aft labeled x, up-down labeled z, and left-right labeled y) which are presented on different sub-screens. The vibration analysis only functions when the engine is running and a valid rpm signal is detected.

In regards to the vibration graph, the vertical axis represents the amount of vibration energy and the horizontal axis represents the frequency spectrum expressed as multiples of crankshaft rpm. When the engine is running, the screen will come alive with a waveform that represents the engine motion, presented in a spectral format with the crankshaft energies appearing at the 1x mark on the bottom scale. Propeller vibration will likewise be synchronous with the crankshaft vibration. Other sources of vibration will tend to produce energies at other frequencies.

For example, camshaft vibration tends to accumulate at the .5x mark, since the cam turns at 1/2 the rate of the crankshaft. Magneto vibration will appear at 1.5x mark in a 6-cylinder engine. Alternator vibration may appear somewhere around 3x or 4x, depending on the ratio it is driven at.

A gear-driven alternator may appear in a different axis than the crankshaft does if it is mounted at 90deg to the engine, although ANY source of vibration will show some energy in all three axis. Complex vibration as generated by reciprocating machinery will also produce a great number of harmonic spikes, which at first glance may seem confusing. The user should experiment with running the engine at different power settings under different conditions to get a feel for what is a "normal" spectrum for their particular engine. A simplified case of vibration is shown in the following figure:




In the example shown above the main source of energy is at the 1x mark, and represents the crankshaft rpm. The smaller spikes at the 0.5x mark and the 1.5x point are probably created by the camshaft and the magneto, respectively. The user should be aware that a multi-cylinder reciprocating engine produces energies at a multitude of frequencies and directions, which reinforce and subtract from each other to create a very complex waveform. It is the responsibility of the user to gain familiarity with a waveform that is typical of their particular engine, so that unusual readings can be detected and interpreted.

The user may examine the various sub-screens by pushing the top button (PG). There are presently six screens to examine, each of the primary axis (X,Y and Z) and an averaged version of each (denoted Ax, Ay, and Az). The averaged version will be much "cleaner" and contain less noise than the raw measurement and is the preferred screen to examine for each axis. The bottom knob (SEL) controls a cursor which will "snap" to nearby vibration spikes to make it easy to examine them closer. The bottom knob can also be pushed to enter a zoom mode. When in zoom mode, turning the bottom knob will allow you to scroll through the waveform. Continue to press the bottom knob to set progressively higher zoom modes. A further press when at maximum zoom will return you to the overall view.

Pressing and holding the PG button will trigger the G4 to save the present vibration waveform for future reference. The waveform will be stored as a series of hexadecimal bytes in the current log file. Insight can provide a tool for examining this waveform using Excel or a similar spreadsheet. The tool is presently in the earliest functional stages of development, and will be improved over time.

It is expected that the vibration functions will be used as a "condition-monitoring tool". Since every engine and accessory combination is different, everyone's vibration spectrum will look unique and it would be impossible to generalize the interpretation of the spectrum. The user will come to recognize what a "normal" spectrum looks like for their engine and by periodically scanning the vibration screen can recognize when potential trouble is developing. When a new spike appears or an existing spike begins to show signs of higher than normal amplitude further investigation is warranted. The source of the spike can be interpreted by noting its primary axis and its frequency relative to crankshaft RPM as discussed above. By periodically saving their vibration data as discussed above, the user can create a database of reference waveforms for future comparison.

Take Off G Force Screen


Turbulence Display Screen




The G3-4 contains a 3-axis accelerometer sampled at modest rates to measure turbulence and landing shock.

Knowledge of G forces will help the pilot to operate the airplane safely by slowing to maneuvering speed. Landing shock is a good training aid for smooth landings and a predictor of structural damage.

Data logged G force will report unauthorized aerobatic activity or abuse of rental aircraft. It could also be useful in accident investigation.

Measuring Horsepower Screen

G4On a test stand engine horsepower is derived by measuring the twisting force (torque) that the engine exerts on a load.  In fact horsepower is defined as simply the product of torque times RPM.  Therefore if our piston engines were equipped with real torque transducers we could utilize RPM and compute real horsepower. While such torque transducers are commonly used to calibrate turbo-prop engines they actually cost more than a typical piston engine. Sadly there is no practical way to directly measure horsepower in a piston aircraft engine.  But this hasn’t stopped at least one engine instrument manufacturer from making bogus claims to the contrary!

REMEMBER:  There is no practical way to truly measure horsepower.

If you planned to use your horsepower display to gauge take off performance or measure engine health you can forget it. In fact, dynamometer tests of so-called horsepower displays revealed NO CHANGE in indicated “horsepower” even when individual cylinders were completely disabled!

The Insight Approach to Power

Despite some limitations we elected to put a power display in the G4 graphic engine monitor.  To prevent any misconceptions we called it “Theoretical Horsepower”, and under certain conditions it actually does a pretty good job of reporting horsepower. One dependable metric of power is fuel consumption. At peak EGT and leaner where ample or excess oxygen available to consume the available fuel horsepower is a linear function of fuel flow. At richer mixtures where some fuel remains unconsumed and doesn’t contribute its full power potential the simple linear relationship falls apart. Prior to leaning to peak the display is challenged to deliver an accurate horsepower display but once peak has been reached the rich-of-peak accuracy will improve.

One limitation of the fuel method is that it is not sensitive to engine faults that can significantly affect the power produced. For example, a cylinder without ignition won’t combust the fuel to produce power, but will nevertheless continue to consume it. So don’t expect to diagnose engine performance issues with the fuel flow approach to horsepower calculation.

What good is a fuel flow based horsepower calculator? The intended purpose of the theoretical horsepower display is to provide an indication of power for leaning purposes. For example, lean-of-peak operation is not recommended at power settings greater than 65%. It is interesting to see the reduction in horsepower that accompanies lean of peak operation.

The Insight Approach to Performance Measuring

While the G4 does not directly measure true horsepower (remember that no engine monitor does) it does measure the EFFECT of horsepower on takeoff acceleration. This information is displayed on the “Take Off Performance” screen and recorded in the log file too. Acceleration is direct function of engine thrust and other factors like weight, runway conditions, slope and even tire pressure. Of course, ambient conditions like altitude and temperature will affect engine power and therefore take off performance.

Insight announces the next big breakthrough in engine monitoring.


In G Series Software Version 208 the G3-4 has a new page that displays data received from the TAS-1000.

The GEM's data-logging capabilities can be extended by receiving air data from a TAS-1000 air data computer. This page shows real-time air data which includes True Airspeed, Pressure Altitude, and Wind Speed and Wind Direction all of which are recorded in the GEM's data log along with engine and fuel data.




Insight’s G3-4 is now capable of receiving RS-232 serial data from our TAS-1000 MFDS that includes Indicated Air Speed, True Air Speed, Pressure Altitude, True Air Temperature, Wind Direction, Wind Speed, and Heading in the data log file on every flight.

While the detail in the G3-4 data log is unprecedented – now it is even better.

The G3 engine log system has been transformed to a complete aircraft performance logging system.

Now you can log aircraft performance data right along with your engine data.

The missing link in data log analysis is finally available.

Now you can really tell what’s happening. Much of the black-box functionality previously available only in Jets is now available to you.

The key to operating your aircraft efficiently is understanding its performance. Now every data log is like a performance chart from the flight manual but it is specific to your aircraft and actual conditions.

Don’t forget about the Insight TAS 1000’s ability to fill in your GPS pages with real-time air data, fuel, wind data page and also with wind arrow and wind speed on your moving map.

With no TAS the G3-4 displays only OAT (Outside Air Temperature) but with a TAS-1000 the missing link in data log analysis is finally available.


With the TAS installed in addition to OAT the G3-4 displays also displays

  • TAT (Total Air Temperature)
  • IAS (Indicated Air Speed)
  • TAS (True Air Speed)
  • ALT (Pressure Altitude)
  • WD (Wind Direction)
  • WS (Wind Speed)
  • HDG (Heading)

Turbulence and Hard Landings:

Now we go back in time to capture a turbulent transient or a landing event. 

In the miscellaneous configuration screen the pilot can now set the threshold for the vertical axis G-force.

Every time this threshold is exceeded the G3/G4 records a 12 second interval of the turbulence in the log file.

These twelve seconds consists of data from the 6 seconds before the event and the 6 seconds after it.  

There are two new screens between Two Axis Turbulence and Takeoff G-force which display live G-force and a snapshot of the G-Force from last event (threshold exceeded).

User can view a graph of the last 12 seconds of live data or view the last captured event.

This feature will also capture hard landings.

The graph is automatically scaled for maximum zoom based on threshold.  When the threshold is exceeded the 12 second G-force is also recorded in the log file.

The new transient G-force screen shows you the whole event the moment it happens. You won’t miss a thing. 

The event is also marked and stored in the log file for easy reference later.

The pilot can set the trigger threshold on the G-force screen for normal operation. Just prior to landing the instrument automatically resets that threshold to always capture the landing event. Just 6 seconds after touch down a high resolution picture of the landing is available.

It is all automatic and couldn’t be easier. 

This new feature is available on all new G3 & G4 instruments and is available at no charge to all current customers in the latest update.

Just download and update your instrument from our web site. 

G4  G4

User Configuration


Using the knobs to navigate the G3-4:

The G3-4 has two knobs: PD select page and SEL work within page. There are two functions built into each knob; the push button switch activated by pressing the knob in, and the selection is activated by turning the knob either clockwise or counter clockwise.

The PG knob is used to select the various screens. From the main temperature bargraph screen turn the PG knob counter clockwise 2 clicks to get to the User Configuration screen. Once you are there you do not use the PG knob any more because turning it takes you away from the User Configuration screen.

The SEL button is pressed to select a line for adjustment. When you first enter a screen by default no line is selected. Pressing the SEL button once selects line 1. The selected line is shown in yellow. Pressing it a second time selects line 2. On any line with multiple selections the selected item will be shown in red.

Setting up the G3 Temperature Bargraph Display:

On the User Configuration screen there are some options for setting up the temperature bargraph display. There are three different ways to accomplish this. One method is to use the Auto range function to configure the display for you.
Another method is to adjust the MAX EGT TEMPERATURE and AUTORANGE INFLECTION parameters manually, and a third method is to set the bar heights visually on the main screen.

On line 2 (EGT AUTORANGE) there are 3 possibilities ON OFF and SAVE. After pushing the SEL button until this line is highlighted in yellow, the SEL knob may then be turned to make a selection on this line. When on line 2 turning the SEL knob fully counter clockwise selects nothing. From there turning the SEL knob one click clockwise selects ON. The current selection is shown in red. Turning the SEL knob another click clockwise selects OFF. And one more turn clockwise selects SAVE.

Using the Auto Range function (Method 1):

To turn OFF the auto range capability on the User configuration screen:

Press the SEL button twice to select line 2 (EGT AUTORANGE).
Turn the SEL knob to select OFF on line 2.
Press the SEL button to select line 7 “SAVE CONFIG”
Turn the SEL knob to select YES on line 7.
Press the SEL knob to save the choice.
We have now turned off auto ranging.

To turn ON the auto range capability on the User configuration screen:
Press the SEL button to select line 2. (EGT AUTORANGE).
Turn the SEL knob to select ON on line 2.
Press the SEL button to select line 7 “SAVE CONFIG”
Turn the SEL knob to select YES on line 7.
Press the SEL knob to save the choice.
We have now turned on auto ranging.

In order to use the auto range function it must be turned on as described above. Once this function is enabled, the G3-4 will automatically adjust the EGT MAX TEMPERATURE and AUTORANGE INFLECTION to be appropriate for the highest temperature reported by the probes.
You should now take the airplane and perform a typical flight.
The G3-4 will analyze the EGT temperatures and scale the temperature bars as required so that the entire temperature range measured by the EGT probes is displayed on the main bargraph screen.
It is important to realize that so far this adjustment is temporary. If we want it to remain permanent we must return to the User Configuration screen.

To save the results of auto ranging:

  • Press the SEL button to select line 2 (EGT AUTORANGE).
  • Turn the SEL knob to select SAVE on line 2.
  • Press the SEL button to select line 7 “SAVE CONFIG”
  • Turn the SEL knob to select YES on line 7.
  • Press the SEL knob to save the choice.
  • The results are saved, and auto ranging is turned OFF.

The main temperature bargraphs should now be scaled properly for this individual airplane on all subsequent flights.
Auto ranging may be turned on and the range relearned as often as desired.

Setting up the G3 Temperature Bargraph display manually (Method 2):

In some cases it may be desirable to set or refine the temperature bargraph screen manually.
To do so, return to the User Configuration screen and make sure EGT AUTORANGE is turned OFF as described earlier. Adjust EGT MAX TEMPERATURE and AUTORANGE INFLECTION directly by using the following procedure:
To set an EGT MAX TEMPERATURE and AUTORANGE INFLECTION on the User configuration screen:
Press the SEL button to select line 3 (AUTORANGE INFLECTION) or line 4 (EGT MAX TEMPERATURE).
Turn the SEL knob to select a value as desired. Notice that adjusting the AUTORANGE INFLECTION affects the value of EGT MAX TEMPERATURE and vice versa.
Press the SEL button to select line 7 “Save Config”
Turn the SEL knob to select YES on line 7.
Press the SEL knob to save the choice.


The Autorange Inflection point is the point along the temperature graph at which the scale of the bars change.
Below the inflection point (ie, at low temperatures) readings are displayed with a coarse resolution (the bars go up/down a small amount for a relatively large change in temperature).
Above the Inflection Point (at higher temperatures than the Inflection Point) the bars are displayed in a higher resolution (the bars go up/down more for a small change in temperature).
The net effect is that the dynamic range of the temperature bargraph is increased. In other words, we can show temperatures all the way down to room temperature on the bargraph yet still show small changes in temperature at the airplane’s operating temperature range.
As an example if we set our Autorange Inflection to be 1200 deg then temperatures below 1200 will be rendered with relatively few pixels/degree whereas temperatures above 1200 will be rendered with more pixels/degree to make temperature changes more obvious.
The EGT Max Temperature simply defines the temperature that is represented by a bar that is full screen in height. For example if EGT Max Temperature is set to 1600 deg than a temperature of 1600 deg will be rendered as a bar that reaches the top of the screen.
The G3’s Autorange Inflection is always 400 deg below the EGT Max Temperature. Adjusting one will therefore always affect the other automatically.

EGT Smoothing

The lower the number the faster the sampling but less smooth (jumpier)
The factory preset is 32.

Adjusting the bar heights from the main screen (Method 3):

An alternative way to setup the scale of the temperature bargraphs can be performed from the main screen.
Press the SEL button and a message appears: “TURN-ADJUST BAR HEIGHT”.
By turning the SEL button the heights of the bars may be moved up and down.
Pressing the SEL button twice more returns the G3-4 to its normal mode.
If we return to the User Configuration screen, we will see that EGT MAX TEMPERATURE and AUTORANGE
INFLECTION have been adjusted to reflect our changes to the bar height.
If the adjustment is to become permanent we must select Save Config and set it to yes.

NEW Fuel Screens

Previously, there was no standard color scheme in the configuration screens.

Now, the selected line is yellow and the inactive lines are white.
YES/NO in red has been removed by displaying only the word YES or the word NO in green, when saving.
When there is a choice of several items the selected item is displayed in green.
Exactly one item is always selected.
The choices of temperature units are Celsius or Fahrenheit then either Fahrenheit or Celsius will be selected in green.

The FUEL TOTALIZATION screen has been improved and is even easier to use.

This change allows the pilot to see this screen before entering fuel on board.
Also setting initial fuel can be checked and corrected in flight.
Previously the pilot had to enter the amount of fuel onboard before he could view the Fuel Totalization page.
Now both the FUEL TOTALIZATION page and the FUEL SETUP page are accessible at any time.
On the FUEL TOTALIZATION screen simply press the PG (left) button to enter fuel, press it again when done. As before you can top up the tank(s) by turning the SEL (right) knob counter clockwise on the very first click.

Set total fuel onboard before take-off

Your G4 Twin was preset at factory with your usable total fuel

To reach the FUEL TOTALIZATION screen from the main screen:

  • Turn the PG knob counterclockwise one click.
  • Push PG knob to go back and forth between the FUEL SETUP and FUEL TOTALIZATION screens
  • On FUEL SETUP screen setting fuel gallons the lines FUEL ADDED, SUBTOTAL and FUEL NOW color will be yellow.
  • Turn SEL knob to set gallons (Clockwise or Counterclockwise one click for total preset total fuel for your aircraft)
  • At any time, you can push PG knob to go back and forth between the FUEL SETUP and FUEL TOTALIZATION screens to add more fuel.

  Fuel Set Fuel Total


FF Stability

Displays, literally, the stability of your fuel flow over the last few seconds. The smaller the number, the less the fuel flow has varied in the past few seconds. A well-regulated fuel system will have a small number, a carbureted system can expect a larger number. The smaller the number the more likely you are to get an accurate fuel flow reading during the lean-find function. An larger number will make things more difficult.


The Fuel Remaining display on the GEM is very useful but is not without limitations. Understand first that the factory fuel quantity gauges are the only instruments in the panel that physically measure fuel level. They are still the primary indication of fuel level in the airplane.

The GEM doesn’t measure level, but instead measures only fuel flow rate. The GEM totalizes the rate information to account for fuel used. If you know how much fuel you started with and how much you have used you can figure fuel remaining by simple subtraction.

The pilot must supply an accurate starting fuel level for this subtraction to produce the correct fuel remaining result. Should the pilot overstate the fuel quantity on board, the GEM will dangerously overstate the fuel remaining and the endurance time as well. The pilot must be careful and diligent when setting the fuel on board.

Getting the correct fuel total on board is in many cases pretty easy. If you fill up prior to takeoff the number is obviously the total available on board. If you partially fill a known configuration (say tips empty) then the total is easy to calculate. If you partially fill fuel tanks or add an accurately know quantity to a poorly known original value - errors will abound. Unaccounted fuel loss from leakage, fuel vent overflow or theft will of course produce erroneous results. So be careful and the GEM will deliver safe, reliable, and convenient fuel information. But be sure to cross reference the information on the primary fuel quantity gauges. Never trust a single source of fuel information when you have two on board. Fuel exhaustion still ranks highly among accident causes. Don’t let your engine stop until you’re parked.