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Is there a certain minimum temperature we need to turn on pitot heat on light trainers (eg DA40NG)?

In the AFM and checklist documents for the DA40NG, information is given that it should only be turned on when you enter unconditional icing conditions. What I'm wondering is, is there a certain minimum temperature value? For example, we are not in cloud conditions, the weather is sunny and there is no weather phenomenon, but the air temperature is low. For example, is the degree value we need to turn on the pitot heat 10°C, 5°C or 3°C? When it is 0°C, I think it is necessary to open it because it is already freezing.

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2 Answers 2

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The AFM you've posted says to turn on pitot heat in icing conditions. It seems you misunderstand what icing conditions are.

You will not get airframe icing simply because the temperature is 0 degrees. The other requirement is that there needs to be visible moisture, such as clouds or rain.

When I am flying in VMC, I don't use pitot heat at all, because the likelihood of the pitot icing over is close to zero. If IMC, I turn it on at about +2.

Note that this is different from carburettor icing/heat. The carburettor can be affected by icing even in quite warm conditions, depending on the humidity level.

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    $\begingroup$ Diid you mean VMC/IMC? Because you can fly IFR on a gin-clear day $\endgroup$
    – Jamiec
    Commented Mar 22, 2023 at 8:56
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    $\begingroup$ @Jamiec I wrote VFR/IFR because for a moment my brain forgot the terms VMC/IMC existed and are a much easier way of explaining what I meant :) $\endgroup$
    – Ben
    Commented Mar 22, 2023 at 11:15
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There is no limitation listed in the operating limitations, NP, EP, or airplane systems sections of the DA-40NG POH requiring you to use pitot heat only when entering inadvertent icing conditions. You may use pitot heat anytime that you wish, but in an emergency situation of inadvertent flight into icing conditions, the pitot hear MUST be switched on.

One possible scenario where pitot heat may not be utilized is a departure into non-icing conditions from an airport with a high density altitude, since the power being drawn from the alternator to provide pitot heat is reducing the airplane's already limited ability to climb. This should not be a problem with a DA-40NG as the turbodiesel engine has a critical altitude somewhere around a density altitude of 13,000 or so feet. So if you're planning a departure from Lake County Airport in Leadville CO mid August at noon, maybe. But the scenario is pretty absurd and there's a lot more on your plate that just pitot heat.

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  • $\begingroup$ If you are a pilot, what is your personal opinion? At what degree would you turn on the pitot heat in the optimistic weather conditions I wrote above? 5°C, 3°C, 1°C, 0°C or minus degrees? $\endgroup$
    – pilot162
    Commented Mar 22, 2023 at 4:46
  • $\begingroup$ Well. let me ask you: In what conditions and temperature ranges are you likely to encounter structural icing? $\endgroup$ Commented Mar 22, 2023 at 4:49
  • $\begingroup$ If the conditions I mentioned above are present (For example, we are not in cloud conditions, the weather is sunny and there is no weather phenomenon), it is normal to expect icing at 0°C and around. But my question is, is there any limit to this? For example, to turn on the pitot heat, do you wait for 0°C or turn it on at 1°C? $\endgroup$
    – pilot162
    Commented Mar 22, 2023 at 5:11
  • $\begingroup$ @pilot162 That is incorrect. With no weather, you don't expect icing at any temperature. Structural icing requires both freezing temperatures and the presence of liquid water (i.e. clouds or rain). $\endgroup$
    – Chris
    Commented Mar 22, 2023 at 18:36
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    $\begingroup$ @pilot162 It is certainly not normal to expect icing, regardless of temperature, in clear weather. Clear air icing is exceptionally rare because it requires very specific conditions. You don't need to turn on pitot heat, regardless of temperature, unless there is visible moisture or you actually notice ice accumulating. $\endgroup$
    – Chris
    Commented Mar 24, 2023 at 4:51

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