At some airports, some taxiways have taxiway hold short markings (single dashed yellow lines against a black background). Do taxiing aircraft by default need to hold short of these markings if they're not instructed by ATC to do so?
This is one biggest pet-peeves of mine that even old, experienced pilots have missed after years of flying.
Taxi instructions are just that: Instructions, not clearances. Mind you there are some clearances when on the ground aswell, crossing a runway, entering a runway, backtracking, maybe some others.. mostly involving the runway. But a general text like ‘Taxi to holding point Charlie via Golf’ is an instruction.
Ok, so the difference is just pedantic but there is one big caveat: when you are cleared to land, cross, enter on a runway you are guaranteed the runway is, well, Clear and will continue to be so for the ammount of time you need it to land/take-off.
This is not true for taxi instructions. You are instructed on what path to take on the ground, but the taxiways and route to your runway is most definitelly not cleared of other aircraft (unless we are talking about low visibiliy ops, but just bear with me for now). When taxing you are still supposed to look out for other trafic and try to avoid hitting other airplanes taxing around as much as you can.
You might be instructed to go via one taxi path and then later told to give way to another aircraft comming from your left. See how the path has not been ‘cleared’? It is not a clearance.
All this talk to sum up: entering/crossing a runway is a clearance. Crossing a (non-mandatory) taxiway holding point is not. Is the answer slowly building up ?
Crossing a runway hold short makrking (two dased lines and two solid lines) you need clearance.
Crossing a taxiway holding marking (or intermediate holding position, or cat 2/3 holding when not in low-vis) does not require one.
A taxi clearance from ATC to a specific point on the airport gives the pilot authorization to cross all hold short markings or hold position markings for intersecting taxiways up to the clearance limit of his taxi instructions without stopping. If a pilot is given a hold short clearance at a certain position, he must stop and ask ATC for permission to proceed. If there is no conflicting traffic as the pilot reaches the hold position, ATC will normally give prior authorization to cross that hold point before the aircraft reaches it. Any position markings that require the aircraft to hold will be given in the original taxi clearance and would have been repeated back when receiving the taxi clearance. If not previously cleared beyond a hold point, the pilot must STOP until further clearance is authorized. Runway Holding Position Markings identify the locations on a taxiway where an aircraft MUST STOP when a clearance has not been issued to proceed onto the runway and no part of the aircraft can extend beyond the holding position marking. This is usually the last position of a taxi clearance limit and normally would be a change of frequencies for take-off authorization. One point to remember: if at any time you are in doubt of of your instructions, STOP! Don’t be embarrassed to ask questions of the controller. It’s okay to ask for directions or for progressive taxi instructions, if you are not familiar with the airport or route of taxi that has been assigned.