So let’s try one of Einstein’s famous thought experiments. Flight AC 111 inbound to YYZ suffers a cracked windshield. (Not an uncommon occurrence if you follow the Aviation Herald). The next flight AC 222 bound for YVR is delayed for four hours while they replace the windshield. This will be declared a safety delay, and I suppose it’s hard to argue with that. No compensation payable.
The third flight of the day, AC 333, outbound from YVR is delayed for four hours due to the ubiquitous “late arrival of the inbound aircraft”. Or so it has been up until now. But first of all, “late arrival of the inbound aircraft” is not the cause of a delay, it is the result of a delay further up the line. So now, will this delay be held out as being caused by the “late arrival of the inbound aircraft”, which leaves room for an argument over compensation, or will it be declared as a delay caused by a cracked windshield and therefore a safety delay?
I can imagine many permutations as this game plays out.