Q. Someone traveling by plane can he face the bathroom wall or door while davening?
A. See Shulchan Aruch (O.H. 83: 1). Mishna Berura (5) rules that one should not daven facing the walls of a bathroom. However, Igros Moshe (E.H. 1: 114), is lenient regarding our bathrooms since everything is flushed. He argues that the doors and walls are also usually made of two layers, with only the inside plate facing the bathroom.
Halichos Shlomo (19: 38), Shevet Halevi (4: 10) and others are also lenient.
Horav Shlomo Miller Shlit’a opinion is similar.