Here's a story from my recent trip. It's a bit wordy but stick with it.
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The previous week while waiting at JFK on a rainy evening for my Delta flight to Zurich, an announcement came on the PA about the flight to Paris at the neighboring gate -- a plane from Detroit had been delayed 2.5 hours which was carrying the third pilot for the Paris flight so they'd have to push their ETD back three hours. Unsurprisingly, this was greeted by the waiting passengers with groans and general annoyance. All of us at the Zurich gate looked at each other and thought "sucks for them but our flight is listed as on time!"
Over the next 45 minutes, Delta dutifully gave PA updates every ten minutes about the ETA of the Detroit plane, which kept being further delayed. Finally, they said "Good news! A replacement pilot has been located in the area and is currently en route to JFK!" For the next half hour, no joke, they gave updates every few minutes about his whereabouts (e.g. "He's currently on the Long Island Expressway; traffic is light and he's making good time;" "He's now on the Van Wyck Expressway and should be here in 15 minutes!"). While it was praiseworthy for Delta to keep passengers properly informed (usually the opposite happens), at the same time it felt a bit bush league, more like a bus company than a global airline. Eventually, they started loading the plane; the pilot arrived; and the flight took off 90 minutes after the scheduled departure. Thus, it could've been worse.
At the same time that the Paris plane left the gate, we learned that the pilot on the delayed Detroit flight was now OUR third pilot, which would push the departure back 2.5 hours and that's the way it panned out. I was disappointed because (I know, first-world problem) that killed my arrival-day plan to spend the afternoon skiing at
stunning Rigi, 50 minutes from Zurich airport.
Instead, I stopped for provisions at Lidl:
... and had cake and coffee along Lake Zug -- one of the bodies of water that I should have been viewing from Rigi!
After that big windup, my question -- is it typical for airlines to have no redundancies in place and depend on the punctuality of an incoming flight for critically important crew members during the peak evening period at a major airport prone to delays? I usually fly United overseas out of Newark and have never encountered this.