Steven P. McNicoll wrote:

I don't know how it is in the USA, but in this part of the world, a taxi
instruction does *not* imply the right to cross a runway.

Why not? What's the point of an instruction to do something if it cannot be
done without additional instructions?

The point is that taxiways are managed by Ground but runways by Tower.
Ground doesn't know what happens on the runways, Tower doesn't care what
happens on taxiways. It goes even furter: Often Ground controllers are
employees of the airport, Tower controllers are employees of ATC. Ground
"controllers" needn't even be controllers at all.

Ground gives you instructions where to taxi and which taxiways ot use,
but this doesn't imply the right to enter a runway. If you must cross a
runway, you hold short of it, switch to Tower and ask for permission to
cross it. After crossing, you switch back to Ground.

Usually Ground will say something like "Taxi via x to holding point y,
hold short of runway z, contact Tower 123.45", but if they omit the hold
short part, this doesn't imply anything.

Good ATC is designed to not have two or more aircraft authorized to be in
the same place at the same time.

As I pointed out (before you ask: in my first three paragraphs), this
wasn't the case.

Stefan