Needs to be a fast mode of transport to keep crew duty hours down, so ground vehicles are out. I was once on a plane at Dublin airport that had to wait for a few minutes behind a small jet that turned out to be the RyanAir (UK and Ireland low cost carrier) company LearJet which they use for positioning flight crews in an emergency or time sensitive situation. Surely United should have chartered a small jet to get crew there, should be doable pretty quickly?