It should be ok to wear contacts on an airplane as long as you get enough sleep the night before traveling to prevent your eyes from getting dry or irritated. The air on airplane is quite dry and you find your contacts will dry out a bit. Take a little bottle of rewetting eye drops if you are worried. However, if you are on a long flight, the air in the plane is relatively dry and contacts can become painful once your eyes have dried a certain amount. In this case it is better to wear glasses.
You had better not to do that. There are a few reasons to proof it.
Firstly, your eyes would have lower oxygen supply, there is no pressure to your eyes when you are at the sea-level. But the oxygen would reduce when the plane is flying, so that it would make your eyes feel uncomfortable.
Secondly, your eyes would feel low humidity. Though you may consider taking rewetting drops to your eyes, almost all airports would not allow passengers to take liquids on a plane.
Thirdly, maybe you can't have a good sleep on the air because rarely people would wear contact lenses to have sleep, unless it has designed for it. If you have to wear glasses, you have better prepare a pair of rimed glasses when taking a plane.
Of course you can. You can wear contacts at anytime except for sleeping or near some dangerous things like fire. It is very convenient to wear contact lenses on an airplane and it won't cause any discomfort. Just remember to keep your eyes moist and avoid wearing them for too long. Hope this will be helpful.
You'd better not, especially if you're just suffering from some kind of eye disease. When you are flying thousands meters high above the earth, the atmospheric pressure around you is much lower than that on earth. So this change of the environment will certainly lead to the stress response to your eyes, and the intraocular pressure will change consequently. When your eyes are in a normal and healthy condition, you can probably tolerate this change, but if you have glaucoma or high intraocular pressure, wearing contacts on an airplane could be very dangerous and act as an incentives of some serious disease. So, it's much safer to remove them in such a circumstance.