WN 5072 ONT-PHX is scheduled to arrive at 4:58 PM. On Sunday it arrived a few minutes late at 5:07 PM. WN 2273 PHX-SEA is scheduled to depart at 4:55 PM. This looks like an impossible aircraft routing until you consider the planned inbound aircraft for flight 2273 comes from flight 1299 PVR-PHX which is scheduled to arrive at 3:18 PM, leaving plenty of time before it departs to SEA 97 minutes later. However, on Sunday 1299 was late in to Phoenix due to a late inbound aircraft. Flight 763 SNA-PVR brings in the aircraft for outbound flight 1299 to PHX. On Sunday, flight 763 departed SNA 5 minutes early at 8:55 AM but was diverted to LAX from over Baja California after it had already been flying toward PVR for about 50 minutes. The aircraft arrived in LAX at 11:16 AM. At LAX Soutwhest swapped the flight to PVR to a new aircraft and it left at 1:15 PM and arrived at 5:59 PM. They did a quick international turn in PVR and departed at 6:42 PM and arrived in PHX at 7:01 PM. So Southwest knew early in the day they had a problem with flight 2273. Rather than delay 2273 to SEA until at least 7 PM, they took the aircraft coming in to PHX from ONT at 5 PM and sent it out to SEA at 5:59 PM, saving at least an hour and a half for the customers on flight 2273.

This is a perfect example of how complex airline operations are and how the root cause of a delayed flight may not be immediately apparent at first glance. All things considered, Southwest did a good job minimizing the impact.