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These two aircraft operate in the Antarctic: the image shows their undercarriage adapted for the snow. The nearest plane (a DHC-6 Twin Otter) has had its wheels completely replaced with skis. The other (a DC-3 / BT-67) has had a toboggan incorporated under each of its main wheels.

Basler BT-67 and Twin Otter in the Antarctic source

The DC-3's wheels protrude below their toboggans, allowing the wheels to support the aircraft's weight on a typical runway. When it flies to the Antarctic, its toboggans are presumably there to stop it sinking in the snow.

However, the Twin Otter is entirely reliant on its skis to support itself. The question is - are planes with only skis capable of safe, regular runway landings? Or are they necessarily restricted to snow?

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Yes a Twin Otter on straight skis can land on a bare paved runway... once.

It will then need to be jacked up and the skis replaced with wheels, or at least some kind of trolly gear installed under the skis to let it be moved. The skis will have to go in to have the bottoms (usually Teflon sheet riveted/screwed to the bottom) replaced. In other words, it's as if you were downhill skiing and ran out on the parking lot that was bare pavement. You aren't going anywhere unless you take them off or start walking with them.

If the runway has a layer of compacted snow on it, that is fine and you can land and take off same as on wheels.

If there is no requirement to operate off bare pavement, straight skis are preferable over wheel-skis, like the DC-3 has, because there is a significant weight saving, maybe several hundred pounds, when you factor in the ski raising and lowering system hydraulics and mechanism, and the weight of the wheels and brakes that are eliminated. So if there isn't a bare paved runway to have to deal with, you run on straight skis to get the payload benefits.

There are paved airports in Antarctica, but to the extent the runway is bare surface at times, they will normally maintain a dedicated ski runway of compacted snow nearby so airplanes like that Twin Otter can come and go. And obviously, the DC-3 can go where it wants.

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    $\begingroup$ I would venture a guess that the Twin Otter could handle a grass-field landing and that this would be far less detrimental to landing on pavement of any sort. Might still require ski replacement, but would have a chance of them surviving for a second landing. $\endgroup$
    – FreeMan
    Commented Mar 21, 2023 at 17:11
  • $\begingroup$ Grass would be ok, and if the grass was thick enough, and wet, you could probably take off from it. $\endgroup$
    – John K
    Commented Mar 21, 2023 at 17:13

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