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NOTE: For leaning instructions always consult the Aircraft’s Operations Hand Book.

Read what Teledyne Continental Motors Inc. says about Leaning -

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Read what Textron Lycoming says about Leaning - Click Here

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With the price of fuel at an unimaginable high, operation lean of peak is more popular than ever.

Instruments designed for rich of peak operation do not meet the new requirements to safely operate lean of peak.

Since the introduction of the Graphic Engine Monitor in the early 80’s a new leaning procedure has been developed. Once frowned upon, leaning past peak to operate on the lean side in cruise is now widely used to save fuel. Since leaning with reference to temperature was first used in the early 50’s, the distance from peak has also been used to define a mixture setting. The term “75° rich” is universal and means 75 degrees lower than the peak temperature on the rich side.

Leaning has always employed a relative number referenced to peak temperature. It is the only consistent metric available because the absolute temperature varies with altitude, power setting and outside air temperature.

The G3 offers a unique new function that facilitates leaning on both the rich and lean side of peak. In previous generation instruments the peak temperature was used behind the scenes to control flashing of a column to identify peak, but it was never displayed to the user. The new instrument doesn’t display the peak temperature but goes one step further to display the distance from peak on either the rich or lean side. This matches the mindset of pilots since the 50’s so it’s what the pilot really wants to know in first place.

Previously the pilot had to remember the bar position and move the mixture to drop a few bars to enrich the mixture. Now the pilot may reference the temperature difference display directly. The temperature difference information is calculated relative to peak EGT so it is only available for display during leaning after peak has been reached. After reaching peak a column width box appears on top of the EGT column containing the temperature difference from peak.

The instrument incorporates fuel flow analysis to also determine which side of peak the mixture setting is on. It prefixes the temperature with an R for rich or L for lean. It further distinguishes Rich and Lean by colour.

The box and number are in white on the lean side and cyan on the rich side. The pilot may decide to operate at a certain temperature delta and tune the mixture until the desired number is in the box. But to make it even easier to operate at a certain predefined temperature difference a user settable threshold is provided. Reaching or exceeding this threshold is annunciated by the temperature box changing from hollow to solid filled. Precise leaning to a predetermined setting can be as simple as moving the mixture until all the boxes turn solid.

The basic G3 cruise-leaning procedure is as follows:

Establish cruise altitude and cruise power. Make initial trim adjustments, etc. as needed to establish cruise.

Perform a coarse leaning or preliminary leaning of the engine until the fuel flow is a couple of Gal/hr more than the normal cruise indication. Pause for two minutes to allow the engine to stabilize and cylinder head temperature to return to normal. It is advisable to allow up to five minutes for the turbocharger (if so equipped) to stabilize in output before attempting final leaning. During this time you can make final trim adjustments to the airplane, reset cowl flaps, etc.

Set the lean threshold as described.

Setting the lean threshold

The user may set the threshold anywhere from 0-99 by pushing the lower button twice and then turning the knob to set the desired number. When complete a short push of the bottom button will clear the threshold setting message.

Now slowly lean the mixture until one of the EGT lean boxes appears at the top of the EGT bars. This final leaning should take about five seconds. The first lean box to appear on top of the EGT bars column of bars identifies the leanest cylinder (the first to reach peak EGT). Continue leaning until the lean boxes appear on all cylinders. To operate rich of peak, move the mixture control in the rich direction until the boxes show solid cyan with an ‘R’ number inside in black. To operate lean of peak, move the mixture control in the lean direction until the boxes show solid white with an ‘L’ number inside in black.

Note: Engine manufacturers differ in their approval of operation at peak. Lycoming recommends operation at peak for power settings of 75% and less while Continental recommends operation at peak for power settings of 65% and less. 

Do not lean to peak EGT power settings greater than those recommended by the manufacturer.

This procedure may not be applicable to all engines. In some aircraft the mixture may be dictated by other parameters.

Restarting the leaning process

Restart the leaning process and reset the peak indications at any time by pushing and holding the bottom button for about 3 seconds until the indications disappear. The user should enrichen the mixture to the rich side of peak and lean from there.