US-China and Tel Aviv-New York top list of busiest US airline routes by seat load

Other international routes with high SLFs included Xiamen-Los Angeles (96.7%, Xiamen Air), Doha-Dallas/Fort Worth (95.0%, Qatar Airways), Shanghai Pudong-New York JFK (94.4%, China Eastern), and Kraków-Chicago O'Hare (94.4%, LOT Polish).

On domestic routes, Dallas Love-Boston led with a SLF of 95%. Southwest Airlines first launched this connection in August 2015, but by May 2024-April 2025 offered only weekly or twice-weekly service—much less frequent than previous years' daily departures. Cirium Diio data shows that out of nearly 14,000 round-trip passengers transported during this period, most were connecting rather than local travelers.

Additional high-SLF domestic routes included Dallas/Fort Worth-Honolulu (94.6%, American Airlines), Baltimore-Aruba (94.6%, Southwest), and Charlotte-St Croix (94.3%, American Airlines).

Seat load factor measures how much available seating capacity is filled by passengers on a given route or network segment. While a high SLF can indicate strong demand or good performance, experts note that it does not guarantee profitability if achieved primarily through low-yield traffic or on long-haul sectors where costs are higher.

Hub carriers may continue operating some high-SLF but low-yielding routes because they feed connecting traffic into other parts of their networks—supporting overall viability even if individual route margins are thin.

The constrained capacity seen on several international markets is likely contributing to these elevated SLFs as airlines adjust schedules post-pandemic or due to geopolitical factors.