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Does anyone know what the yellow arc on the EGT gauges represents? I haven't been able to come up with any information on them.

Thanks,

Jesse

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Perhaps I should clarify. I am asking about this because I have always recognized a yellow arc marking on any gauge to be a caution zone. But in the 690 I find myself operating within this apparent caution area in many flight regimes even with moderate power settings. And in fact there is quite a separation between these temps and the red line implying that it is satisfactory to operate at temps higher than the caution area. Very confusing. So I thought there may be more to the explanation.

At any rate, If anyone has some knowledge of this I would sure like to hear your explanation.

Thanks,

Jesse

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Jesse,

First, let me explain what Carenado has modeled.  The airplane is a 690B, however it was modified to carry TPE-331-10 engines.  The -10 engines use EGT gauges vice ITT gauges because the "bigger" engines ran so hot that normal thermocouples were not available to measure ITT.  So, they used the cooler running EGT instead, measured at the exhaust of the final turbine stage.  The most similar factory airplanes that used EGT were the 980 and 1000 versions.  I have a Pilot Operating Handbook for the 980 and it does not address the yellow arc on the EGT gauge at all.  The starting limit is 770 and otherwise the limit is 650.  Those may or may not be the actual physical temperatures and the measurement points.  The system uses a computer that considers ambient temp, pressure, back-pressure to compute a SRL (single red line) value for EGT.  The gauge indication is then corrected for those factors.  The pilot only has to remember the 650 maximum (or 770 for start, but that is actually marked on the gauge).

I know that doesn't help, but apparently the yellow arc has no meaning.  Or at least not enough meaning to mention it in the POH.

I've got a fairly major redo of the 690B in work.  

Regards,

Bill   

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Hi Bill.

Thanks for taking the time to post the comprehensive information. It's all right in line with what I have been able to find, also. And that's after considerable digging around.

Still hoping that some reasonable explanation will present itself at some point. Sure makes nervous flying around with a gauge so regularly indicating in what appears to be a caution range; even if it is just a simulation. 🙂

Also, looking forward to your mod updates.

Jesse

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