http://revach.net/article.php?id=3765

Section: Halacha   Category: Tefila
Rav Moshe Feinstein: Davening On An Airplane

If a person needs to daven on an airplane it is permitted to daven Shomeh Esrei sitting down, if standing up is difficult and it will disturb him from davening with the proper Kavanah. However he should stand up prior to the parts of the Shomeh Esrei that require bending down. After he bends down he may sit down again. If the plane lands before the end of the Zman Tefillah he is not obligated to daven again even though he davened while sitting. (Igros Moshe OC 4:20)

Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation.  Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.