Most airlines release "blocked" seats (including 5F) exactly . Set an alarm. At T-24 hours, open the app. You will often find 5F suddenly available even if it showed as "occupied" yesterday. Why? Airlines hold row 5 for elite frequent flyers. If no elites claim it by T-24, it becomes free.
If your inbound flight lands at Gate 5F (some airports use lettered gates, like Terminal 5, Gate F) and you have a 30-minute connection, you are likely sprinting. Gate F is often in a low-cost carrier satellite terminal far from main security.
Important: If you booked through American Airlines but the plane is operated by "5F" (Air Arctic), your baggage liability shifts to the operating carrier. Always confirm the "Operated By" line on your itinerary.
Singapore Airlines flies Singapore–Tokyo–Los Angeles. A traveler can book just Tokyo to Los Angeles on Singapore Airlines – even though Singapore is neither Japan nor the US.
When booking, use sites like SeatGuru and input "5F" for your specific flight number. An "airline 5F" on an Airbus A380 (upper deck) is a private suite; on a CRJ-200, it is a cramped seat next to the engine.