When did you last see this?

NO!  Not the Blue sky. 
NOT the Gull, that's an unexpected Bonus.
I learnt, recently, from "an impeachable Sauce" that in any 24 hr period something in the order of 500 planes pass over Penrith.
500 ÷ 24 = 20.88 planes per hour; let's call it 20. I think we can all divide 60 by 20, I think even I can do that.  You'd think three planes per minute would leave the odd vapour trail or two ("Wooden Chew").

I suspect you last saw it (Barring the COVID period) About 11 years ago, almost exactly.  I stole and modified a headline, from the 10 it said.
"Where were you 11 years ago when the Icelandic ash cloud shut down Europe?"

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For my record only:-
Had PAT fluid replaced/topped up.
Looked up PAT fluid.
Do NOT ask for an explanation.
Resulting in an end to messages like:-
Service overdue.
Remote battery low.
Engine system service required.