Great video, those white gloves would not stay white for long prepping an Australian locomotive! Cannot see the point in tooting the whistle during cab prep when the train is not moving? Excellent!
I'm not a railway staff, just my personal understandings: These horn signals appear before operations that could cause possible danger. When you raise the pantograph on a locomotive with problematic circuitry, arcing might occur. Unexpected movement might happen during brake test if the train has a braking system issue.