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I asked this question about what "the thing on the windscreen of some Piper aircraft is". It came out that it is used as small anti-icing.

The user Jules asked following in a comment of an answer:

Is de-icing this small an area generally beneficial for longer flights, or is it "just good enough" for a landing at the nearest airport if the ice buildup is starting to seem hazardous? (Asking as a non-pilot)

I also think it's a good question, but unfortunately the author of the answer didn't answer.

Thank you!

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    $\begingroup$ I also answered that original question. In my answer I attempted to answer Jules's vague question (and your question) in regards to both the practical and regulatory aspect (i.e. the hot-plate has to be sufficient "so that the pilot has adequate view for taxi, takeoff, approach, landing, and to perform any maneuvers within the operating limitations of the airplane."). Is there anything else you wanted clarified? $\endgroup$ – J Walters Feb 7 '17 at 20:02
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    $\begingroup$ Possible duplicate of What's that "frame" in the windshield of some piper aircraft for? $\endgroup$ – J Walters Feb 8 '17 at 21:51
  • $\begingroup$ I disagree that this is a duplicate. The linked question seems to be asking what the windshield deicer is, and this question seems to be asking whether or not it can be used during normal operations or only as an emergency measure. $\endgroup$ – Steve V. Feb 9 '17 at 4:31
  • $\begingroup$ Looks like I overlooked it. Sorry for that. But I would still be interested if there are any problems when landing or in general with just a small window to look through. $\endgroup$ – Noah Krasser Feb 9 '17 at 16:59
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Those hot plates, in my experience, are useless. The only reason we had one on our PA34 cargo plane was to make it legal for flight into known icing. As far as I'm concerned, the whole and entire point of those external hot plates is to check a regulatory box to make the plane legal for FIKI if so certified.

It never once actually kept ice from accumulating and the entire windshield, hot plate included, frosted over on more than one occasion. I recall hoping for strong right crosswinds so I could crab down to the runway using the side window. We checked that the circuit was powered so we knew the plate had power, it was just totally ineffective. Cutting a new pilot loose in that thing for their first low IFR icing encounter was a serious decision.

Now, proper heated windshields with integrated elements work wonders on ice. They also cost $25k per side (twin Cessnas), so they'd better work. The plates bonded to the windshields (on Barons, for example) seem to work OK too though I've never used one. I think the cold air flowing over and under the stand-off hot plates simply overcomes the capabilities of the unit except in the most mild conditions.

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