From a pilots perspective this is actually a little more complex then you would imagine depending on which airport you are at (in Canada). Some examples so you know why this might happen:cossack wrote:YYZ Tower perspective:
Changing frequencies before being told to do so on both ground and tower; would you change enroute?
Vancouver expects you to know when to change from GND to TWR. The only aircraft they seem to specifically tell to switch frequencies are foreign carriers. And when you do switch to tower, telling them you are there is frowned upon while at other Canadian airports you would be sitting short forever as the TWR is waiting for you to check in ready to go.
Tower to departure changes.... I know the correct answer here is to stay with YYZ tower until handed off but I have made the mistake simply out of habit. Most other airports don't hand you off to departure as it is automatically assumed due to wording in the SID or "contact departure airborne" with the takeoff clearance. YYZ doesn't have that wording so I would be in the wrong to switch automatically. And to my knowledge, CYYZ is one of the few airports that operates like this. So sometimes on the last leg of a 5 leg day, the finger just hits that departure frequency in the backup com. I'll openly admit to being guilty of this once out YYZ.
Just a pilots perspective of how we actually sometimes have to ask ourselves mentally, "what airport am I at?" as each (even though in Canada) have unique little differences that we need to be aware of.