But anyhow, why do you have to come on to this? Once you are agreeing that an airplane is a Tzamid Passil it is anyhow Mafsik because of its size.
I was just looking over that Tosafos in Eiruvin 31. He quotes the Rashba that holds that an Ohel Zaruk is only a problem when it is being held by a person or Keilim. So now, perhaps according to this, an airplane does not have the problem of Ohel Zaruk!
The next question is, what about a bus? First of all there might not be a Tefach all over and the Tuma can enter. But that aside, are the tires part of the bus or are the considered separate Keilim and render the bus an Ohel Zaruk. This leads us back to the Sugya of Muchni.