This arrangement certainly has some attraction for an airline. Consider the "normal" case where airline pays for TR and bonds joiner for x years. After six months new guy gets offer of shiny jet job and leaves. Airline asks for bond back. Departee tells them to "s*d off!". Lot of hassle for airline, do they go through the courts?.
But if new guy has to pay up-front and then decides to leave before agreed time, airline doesn't lose out.
Beancounters will love it!