Quite straight forward really.
The hold short instruction is usually given by the ground controller as a limitation on a taxi clearance, an intermediate point at which to hold enroute to the active runway. Bad things happen if you pass this point without further clearance
It can also be given should the pilot state the readiness for takeoff to the tower controller upon reaching said active runway - in other words, a reply from tower to a pilot prompt for a TO clearance. If it's no, then "hold short" will be issued.
As far as tower controllers are concerned, work load dictates that the pilot be on frequency but don't call them because they'll call you. It's not up to the pilot to initiate the chitchat and cause a hold short instruction to be issued and tower controllers don't initiate contact only to issue "hold short". If the pilot keeps the trigger finger off the transmit button ( ever notice how some muppets just love to talk?) the first tower call will be Position and Hold or Cleared for TO.
It's really all perfectly simple and straight forward, a bit like moving your clothes from the lower peg to the upper peg unless you've had your house master's chit countersigned by matron because you're not playing cricket that afternoon and your parents are visiting.
No ambiguity at all, unlike a conditional "line up and wait" which really is an accident waiting to happen.
edited because the original made even less sense than I thought it did.
Last edited by XL5; 7th Mar 2006 at 04:53.