Ditching analog engine instruments

The aircraft’s vacuum system is removed, and the new AI and DG/horizontal situation indicator (HSI) are installed in the same instrument panel holes. It’s a terrific upgrade that adds situational awareness (since most units display much more information than their analog counterparts) and reliability (solid-state operation means no moving parts to break or wear out).

 

Consider the options

A digital engine monitor provides a similar increase in situational awareness and safety, but choosing the options you desire and a location in the panel to install it can be a bit more complex than with AI/DG/HSI upgrades. Here are some considerations for removing analog engine gauges and replacing them with a digital engine monitor.

FAR 91.205(b) requires aircraft to have the following engine instruments installed and operable: tachometer, oil pressure gauge, and temperature gauge for each engine; manifold pressure gauge for each altitude engine; and a fuel gauge indicating the quantity of fuel in each tank. These instruments can be replaced with one digital engine monitor, available from multiple manufacturers that offer a variety of options for both certified and experimental aircraft.

Digital engine monitors display the FAA-required rpm, manifold pressure, oil pressure, oil temperature, and fuel quantity. In addition, most digital engine monitors can display cylinder head temperature and exhaust gas temperature for each cylinder, fuel flow, fuel pressure, battery volts, amps, percent power, Hobbs hours, tach hours, flight hours, outside air temperature, and more. These parameters are recorded multiple times per second and available for download to analyze later.

Since you may be replacing five or more instruments with a digital engine monitor, and there can be a lot of data displayed in a compact space, it’s important to make sure you like the user interface. Do you prefer buttons or touchscreen? A round, square, or rectangular form factor? Is the text easy to read? What kind of alerts are available and how do they look and sound? All of this should play into your decision making. Consider flying with someone who owns the brand you’re considering, visit manufacturer displays at EAA AirVenture or Sun ’n Fun, or make an appointment with a dealer to try it out for yourself.

Fitting in

For ease of installation, it’s crucial to determine—before you buy that shiny new digital engine monitor—what functions you want the monitor to display, as many functions are optional or may require sensors that do not come with the engine monitor. This affects not only the model of digital engine monitor you’ll buy, but also the sensors and wiring harnesses you’ll need to purchase. AOPA has learned the hard way with its sweepstakes airplanes that your project can be delayed if you don’t have all the components you’ll need on hand before installation begins.

Instrument panel placement is another consideration. Most digital engine monitors fit into the 3 1/8-inch to 3 1/2-inch hole vacated by the tachometer. However, that may or may not make sense for your airplane—particularly if your tachometer is on the extreme right-hand side of the instrument panel. You’ll also need to decide if you will keep your analog gauges or remove them to save weight. The most elegant, but expensive, solution is to have a completely new instrument panel cut so that you can put your remaining instruments exactly where you want them.

Get experience

While digital engine monitors can be installed by any A&P and signed off by any IA (you don’t have to use an avionics shop), you’d be wise to ensure your mechanic has installed a similar monitor previously, otherwise you’ll be paying for their steep learning curve. Gulf Coast Avionics, a Garmin dealer, estimated it will take about 75 hours to install a Garmin GI 275 EIS and run wires to the myriad sensors in a Cessna 172—and that’s with an experienced avionics technician. Options exist to have wiring harnesses custom made to include the sensors you’ll need—which dramatically reduces the time needed to install the engine monitor—but it comes at cost.

After installation, most digital engine monitors require some level of programming by the installing mechanic to set the correct minimum and maximum parameters for your aircraft and to enable optional functions you’re expecting to see.

While all this might sound like a lot of work, the results are worth it. The situational awareness one can gain by looking in one place to monitor your engine’s performance is dramatic. Not only will you know much more about the health of your engine in real time—and over time with data analysis—but you’ll be also warned of potential engine issues you may not have otherwise noticed in flight through digital engine monitor alerts. And that could prove priceless.

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