All but 3 mitzvot can be suspended to save a life.
Prayers should be done standing. OTOH, I've prayed sitting. However, for morning prayers tallit and teffilin must be worn.
The greater question is was it the standing, or the putting on of teffilin and praying in a 'strange' language? There is movement in prayer. So it's not like the person can just sit quietly. Parying will attract attention. Better training of flight crews can mitigate this.
The example I witnessed - the man who blocked the door to the hotel I was trying to enter - he was swaying back and forth, chanting in (I presume) Hebrew, with his eyes closed. He completely ignored all comments and requests to move from in front of the door he was blocking, and when I 'moved' him by shoving as politely as I could, he never acknowledged the fact that I was doing it. He didn't stop doing what he was doing, and I had to literally shove him out of the way so that I and others could get by him.
I frankly find it difficult to believe that he was required to stand in that very spot; or that he was incapable of responding to polite requests to step aside. If that's a requirement, then yeah, that's kind of a problem. On a plane, more so. I mean what if they guy I ran into had been crossing the street when overcome by the need to begin his prayers? Is traffic supposed to stop and wait quietly whilst he does his thing?
But as noted; although I have had quite a bit of experience amongst the Orthodox communities, I've seen very few people wearing teffilin or chanting loudly in Hebrew. It is unusual for most Americans, I'd wager. Even in communities of Hassidim, you just don't see it that much; either because they mostly perform their religious rituals in private, or because they don't do all those various things.
When my best friend converted to Judaism (reformed), I asked him a lot of questions, because I was curious. Some of the answers he gave startled me with their sheer common sense and respect for others. For example, he chose to keep kosher. But when I asked him if he'd eat pork if it was the only food available, he said of course he would, without hesitation, and he wouldn't feel bad about it either. He said his first commandment was to preserve his life, to survive. He also said that if he lived in a town where he was the only clergy and a man died who was of another faith, he was commanded to perform the appropriate ritual for that man's faith if he could, like a chaplain in the military does. I found that compassionate and very decent. A religion I can have a lot of respect for.
Point being, even though I have deep respect for Judaism, I am not at all interested in experiencing what these gentlemen appeared to have done on the plane. Yes, I would have known what they were doing, having seen it before. But I'm not surprised that most people wouldn't, and it was outrageous - in my opinion - that the men chose to ignore the instructions of the flight crew. I'd have had them strapped into their seats toot sweet. Religious requirements come second to passenger safety - or in this case, that perception.