When a foreign road locomotive (or train) operates over a railroad line with its own crew, the rulebook requires that a qualified engineer (and sometimes a conductor)from the home road be aboard in order to familiarize the foreign crew with signals, slow orders, and other operating and safety matters. The home road engineer and conductor are referred to as a "pilot crew". As someone has mentioned previously, pilots in the maritime world perform a similar function, i.e guiding crews that aren't qualified to navigate a particular harbor or river in order to assure safe passage.