Question: Previously when I have flown, I have been invited to join a minyan on the plane, though have always been uncomfortable about doing so. I am about to fly again. What should I do if asked to join a minyan?
Answer: The Shulchan Aruch (OC 95:1) writes that one must stand with their feet together when reciting the amida.
However, one who has to daven while riding a donkey, in a carriage or on a boat should do so while seated unless it is easy to stand (ibid. 94:4). The Mishna Berura (94:13) explains that it is easier to concentrate this way.
Thus, R’ Moshe Feinstein (Igros Moshe OC 4:20) writes that one can sit for the amida on an aeroplane, especially if one will be less distracted. R’ Shlomo Zalman Auerbach (Halichos Shlomo, Tefilla 8:4) adds that as davening with a minyan during a flight will bother other passengers, one should rather daven the amida while seated.
The Aruch Hashulchan (OC 94:18) writes that one davening while sitting should still (keep their feet together and) bow in the appropriate places, standing in their seat to do so if possible.
Certainly, it is best to avoid davening while travelling if possible. The Mishna Berura (89:39; 42) writes that it is better to either daven before travelling or delay davening until one arrives, even though one will not be davening at the ideal time, though one must ensure that they do not miss the latest time to recite the shema or the amida.
In conclusion, one who needs to daven while on a plane can stand in their seat if they are not disturbing anyone else. One may sit throughout, though should stand to bow at the appropriate places if easy to do so. One must not join a minyan if it will be in the way of others.