Okay, here is my story of vaping on a plane. I told it in the other forum when I got back from Portugal in October of 2019 (and so glad I splurged on that trip, not knowing the Covid bogey was sneaking up on the horizon). It isn't that I can't fly without vaping. I've done it many times, but a trans-Atlantic flight is such a long one, I knew I would enjoy it more if I could vape.
In business class on Tap Portugal, you get your own playpen, shielded from view by a sort of armchair wing on the aisle, high seat back, and a darkened cabin on a night flight. I watched for flight attendants, and stopped when they came out from their curtained area. They weren't looking for vapers or vapor, even though the pre-flight announcements included "smoking is not allowed on the aircraft, including electronic cigarettes", in both Portuguese and English.
I'm not recommending that anyone vape on a plane. I don't want anybody to have an air marshal waiting for them when they exit the plane. I wanted to see if an onboard computer could read my device in use, or if my vapor would cause an alarm to go off, and if other travelers could remain oblivious to my habit. I couldn't have gotten away with this in the economy cabin, but I had a very satisfying experience in business class, vaping unflavored after the gourmet dinner with excellent wine, having a vape after waking from a flight nap, feeling at home, feeling fine.
Vape hysteria has spread to Europe. When I asked my Portuguese tour guide if I could vape, he said "isn't that harmful?" I explained the black market THC/vitamin E oil scandal. I explained to him what is normally in ecigarettes, the pg which is the same carrier for nic as it is for medicine in asthma inhalers, the vg which has internal medical applications such as ear drops, eye drops, suppositories, etc. He said "but the flavorings can be harmful". I agreed with him that I do not know if a flavor, even if 100 percent clean and safe to eat, is safe to inhale, but I told him (the truth) that I vape only unflavored when I'm around others, so they are spared any potential harm from the flavorings. In the end, he became very relaxed about it, and told me to vape freely.
I vaped everywhere I went in Portugal and Spain, but I don't find stealth vaping very satisfying. I did it, in corners of restaurants, blowing the vapor sort of under my arm or down over my chest. I liked white tables, white walls, white curtains, because your vapor disappears there. I vaped freely outdoors.
I took 30 ml. liquid with me for a 9 day trip. You don't vape as much when you're walking around, sight seeing, hiking the caminos, but after stealth vaping at meals, and freely vaping during the evenings in my hotel rooms, I got home with 2-3 ml. remaining in the bottle. It's a good thing it lasted, because I saw zero vape shops in the towns I visited on the Camino Portugues and the Camino Frances, which are less traveled portions of the Camino Santiago de Compostela.
I vaped all over the airports too, during the waits for flights and the stopovers, in the US (Newark) and abroad (Porto airport). There is always an abandoned gate with the lights out, and I found there just aren't any airport authorities patrolling for vapers, at least none that I could notice, and I was watching out for them.
That's my true story, but I admit to being a risk taker. I remember smoking pot on a plane, in the economy cabin, a long time ago when I was younger and had shit for brains. Big hit from a tiny one-hitter pipe, holding it in until nothing came out, didn't get caught.