Is Ethernet used for vital controls on aircraft? That would be a more critical application than trains, given that on an aircraft you usually can't just dump the brakes and stop if you are in trouble.
The aviation industry is in recent years using a more robust implementation of ethernet, known as AFDX (Avionics Full-Duplex Switched Ethernet):
http://en.wikipedia.org/wiki/Avionics_Full-Duplex_Switched_Ethernet
Which itself is part of a standard known as ARINC 664.
http://en.wikipedia.org/wiki/ARINC
Though implementations vary by manufacturer.