Looking on the internet deeply has found these results:

sitting in the plane is the most popular phrase on the web.

sitting on the plane 1854,000 results on the web	sitting in the plane 1971,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I had a great time sitting next to you on the plane. For about the last two months, drivers working for the European Parliament have been repeatedly stopped and checked by the police, as was the case on Monday at Strasbourg Airport, while Members of Parliament were sitting on the plane. I've been sitting on planes for 72 hours. I really enjoyed sitting next to you on the plane, Chris. But was he sitting next to you on the plane? Do you think, if you hadn't open that door late that night in Mexico city the two of us would be sitting on this plane now? I was sitting next to her on the plane. They were on the plane sitting a couple of rows behind me.	They were on the plane sitting a couple of rows behind me. Who's sitting in the plane? That is a photograph sent by my liaison in the Paraguayan Army of your private plane sitting in an airfield just a few miles away from The Triple Frontier. I've been sitting on planes for 72 hours. Wait till I'm sitting in a real plane. Young man, I'm very nervous about sitting in the middle of the plane or the back of the plane. I would be much happier sitting in the front of the plane, in first class. I've been sitting in that plane for nine hours...

sitting on the plane

1854,000 results on the web

sitting in the plane

1971,000 results on the web

More popular!

I had a great time sitting next to you on the plane.
For about the last two months, drivers working for the European Parliament have been repeatedly stopped and checked by the police, as was the case on Monday at Strasbourg Airport, while Members of Parliament were sitting on the plane.
I've been sitting on planes for 72 hours.
I really enjoyed sitting next to you on the plane, Chris.
But was he sitting next to you on the plane?
Do you think, if you hadn't open that door late that night in Mexico city the two of us would be sitting on this plane now?
I was sitting next to her on the plane.
They were on the plane sitting a couple of rows behind me.

They were on the plane sitting a couple of rows behind me.
Who's sitting in the plane?
That is a photograph sent by my liaison in the Paraguayan Army of your private plane sitting in an airfield just a few miles away from The Triple Frontier.
I've been sitting on planes for 72 hours.
Wait till I'm sitting in a real plane.
Young man, I'm very nervous about sitting in the middle of the plane or the back of the plane.
I would be much happier sitting in the front of the plane, in first class.
I've been sitting in that plane for nine hours...