Rabbi Shlomoh Zalman Auerbach said this in Halichos Shlomoh, 1:95-96:
�It is better to pray Shemoneh Esrai sitting down than to stand in the aisle of an airplane, both because of concentration and consideration of others.�
FOUND IN: Relevance Pirkei Avot (page 107) by Rabbi Dan Roth, year 2007 CE, Feldheim Publishers