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Thread: Winter Hard IFR

  1. #1

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    Winter Hard IFR

    Could you offer a lowest temperature best practice for hard IFR flight during winter for an airplane (e.g. C172) without deicing equipment?

  2. #2

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    Quote Originally Posted by rayds View Post
    Could you offer a lowest temperature best practice for hard IFR flight during winter for an airplane (e.g. C172) without deicing equipment?
    When flying in visible moisture, structural icing is possible starting at 0*C. It remains possible all the way to -40. So anything in that range should be approached with caution.

  3. #3

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    Quote Originally Posted by rayds View Post
    Could you offer a lowest temperature best practice for hard IFR flight during winter for an airplane (e.g. C172) without deicing equipment?
    Best bet is to listen for pireps on the ATC freq. Icing is unpredictable. When there were actual reports of icing, there was nothing, nada. Once we were in textbook conditions for ice and with an escape plan. Nothing. On the other hand, the last time I picked up light iceing was in VMC over the the Gulf of Mexico, 2,500' at plus 2 oat. Go figure. Have an escape plan and listen.

  4. #4

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    “Hard IFR” implies one may be assigned an altitude he doesn’t want and may be stuck there for some time. In my limited experience, I have noticed cloud tops are sometimes the wettest/densest part, and colder than the winds/temperatures aloft forecast indicated.

    I rely on the ADDS Icing Forecast to determine the ice potential along my route and expected altitudes. In a C172, I might accept a low probability of trace icing during cruise only if I could safely descend out of it into above-freezing air. I wouldn’t want any forecast chance of ice while entering the terminal environment through the approach and landing. I want no chance of ice on the windshield while looking for the runway.

  5. #5

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    Quote Originally Posted by rayds View Post
    Could you offer a lowest temperature best practice for hard IFR flight during winter for an airplane (e.g. C172) without deicing equipment?

    "The general rule is that the more ice particles and the fewer liquid
    drops that are present, the less ice accumulation on the airframe. This is because the ice particles
    tend to bounce off an aircraft surface, while the supercooled drops freeze and adhere. As a result,
    ice accumulation is often greatest at temperatures not too far below 0 °C (32 °F), where LWC
    can be abundant. LWC is usually negligible at temperatures below about -20 °C (-4 °F)"

    "Tests have shown that when outside air temperatures (OAT)
    are near freezing, the result is no ice accretion near the stagnation point, but the freezing or
    refreezing of water running back on the airfoil, causing runback ice accretions, possibly behind
    the protected areas. The formation of a ridge is possible. Pilots should be vigilant at OAT
    between -5 °C (23 °F) and +2 °C (35 °F)."

    https://www.faa.gov/documentLibrary/.../AC_91-74B.pdf

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