According to OAG, the four busiest domestic routes in the United States (US) by seat availability in 2024 are:
- Atlanta - Orlando
- Honolulu - Kahului
- Las Vegas - Los Angeles
- Denver - Phoenix
By number of flights, the list of busiest routes changes. Honolulu-Kahului is the busiest domestic route in the US by number of flights. The second-busiest is from Los Angeles to San Francisco, with more than 23,000 flights. New York (LaGuardia) to Chicago (O’Hare) is the third-busiest and had the biggest capacity increase this year. According to OAG, seat availability grew by 17% on this route.
Los Angeles-Las Vegas is the fourth busiest, and Los Angeles-New York-JFK) is the fifth. The transcontinental route has more than three million available seats in 2024. Notably, United Airlines has a significant operation from Los Angeles to Newark but does not fly to JFK. Denver-Phoenix, which is the fourth-busiest by seat offering, is seventh by flight numbers.
4 Atlanta - Orlando
3,470,513 seats
The first route on this list is from Orlando International Airport (MCO) to Hartsfield-Jackson Atlanta International Airport (ATL), Delta Air Lines’ busiest hub. According to Cirium, an aviation analytics firm, there were nearly 3.5 million seats available between Atlanta and Orlando throughout the year. Four airlines operated flights on this route, with Delta Air Lines having the largest market share.
The four airlines are listed below in order of market share:
- Delta Air Lines
- Southwest Airlines
- Frontier Airlines
- Spirit Airlines
That month, Delta had more than 195,000 seats available. With how busy the route was for Delta, it deployed several aircraft types. The list of the planes deployed in May is below:
- Airbus A321
- Airbus A321neo
- Boeing 757-300
- Boeing 757-200
- Boeing 767-300
Though five different aircraft were deployed in May, the most frequently used planes for this route were the Boeing 757s.
Southwest had the second-largest market share with 3,360 flights and more than 532,000 seats. Frontier also had a significant operation. Although Frontier had 1,000+ fewer flights than Southwest, its seat offering was only about 80,000 less. The ultra-low-cost carrier had 2,259 flights and 451,562 seats.
3 Honolulu - Kahului
3,368,476 seats
The route from Daniel K. Inouye International Airport (HNL) to Kahului Airport (OGG) was the second-busiest route by seat offering this year. This is one of the famous island-hopper routes that dates back to Hawaiian Airlines’ origins. Hawaiian operates this route to this date and is one of two remaining passenger airlines operating the Boeing 717, following the recent retirement from Qantas in Australia.
By number of flights, August was the busiest month for Hawaiian, with 1,319 flights. That month, the airline had more than 168,000 seats available. This broke down to up to 22 daily roundtrips between the islands.
The flight between Honolulu and Kahului is just 101 miles long, and the Boeing 717 is the aircraft of choice for these routes. These planes are set in a two-cabin configuration on Hawaiian, with eight first class seats and 120 in economy. ON a monthly basis, Hqwaiian had more than 150,000 seats available on the route.
Although Southwest had about half the number of flights, it was not far behind Hawaiian by seat offering. Southwest had 8,040 flights scheduled, compared to Hawaiian’s 15,223. Despite this, Southwest had 1,407,000 seats available, compared to 1,961,476 from Hawaiian.
The reason Southwest had such a high seat offering is because it uses some of its Boeing 737 MAX 8s to fly between the islands. These planes do not have any premium seats and are equipped with 175 seats in an all-economy configuration.
2 Los Angeles - Las Vegas
3,313,878 seats
The route to Sin City has the most competition of the routes mentioned so far. According to Cirium, nine airlines operated flights between Harry Reid International Airport (LAS) and Los Angeles International Airport (LAX) in 2024. The airlines are listed below:
- American Airlines
- Alaska Airlines
- JetBlue Airways
- Delta Air Lines
- Frontier Airlines
- Spirit Airlines
- Sun Country
- United Airlines
- Southwest Airlines
The gap between the second and third routes on this list is just over 50,000 seats. Although Southwest dominates the market between LAX and LAS, it does not have a large advantage like Delta on the ATL-MCO route and Hawaiian from OGG to HNL. Data shows that Southwest had 5,345 flights scheduled in 2024.
Delta had the second-highest number of flights, with 3,500 exactly. Southwest had 862,223 seats available, compared to Delta’s 567,598. United Airlines had the third-largest market share, with 3,021 flights and 513,201 seats.
Spirit Airlines had fewer flights than United but still had more than 6,000 additional seats. Sun Country is at the bottom of the list and only had one scheduled flight in May.
Southwest’s busiest month by number of flights was August, with 476 total flights and nearly 76,000 seats. The low-cost carrier used all three of its Boeing 737 variants on this route, the -700, -800, and MAX 8.
- Airbus A319
- Airbus A320
- Airbus A321
- Boeing 737-800
- Boeing 737-900ER
Most of United’s operations throughout 2024 were mainline, but the airline did schedule two flights on SkyWest Airlines in August. Like Delta, December is United’s busiest month from LAX to LAS, with 308 flights. For this route, United is using all of its Boeing 737 variants except the -700. This includes:
- Boeing 737-800
- Boeing 737-900ER
- Boeing 737 MAX 8
- Boeing 737 MAX 9
1 Denver - Phoenix
3,205,155 seats
The final route on this list is between two of Southwest’s focus cities, Denver and Phoenix. United has a hub at Denver International Airport (DEN) and is the largest airline there. Phoenix Sky Harbor International Airport (PHX) is a hub for American Airlines. According to Cirium, there were 3,205,155 seats available on the route this year.
Four airlines had service between Denver and Phoenix:
- Southwest Airlines
- United Airlines
- Frontier Airlines
- American Airlines
Over 19,000 flights were scheduled from DEN to PHX throughout 2024, and Southwest had nearly 8,900 of those. Southwest’s operation was nearly double that of United’s, in terms of flights. United had 4,918 flights scheduled and 809,374 seats. Southwest’s seat offering reached nearly 1.5 million.
Frontier Airlines had the third-largest market share with 3,262 flights, compared to American’s 2,142 flights. The ultra-low-cost carrier had more than double American’s seat offering, 642,054 and 305,474, respectively.
At its peak this year, Southwest had more than 850 monthly flights. This was in March, when the carrier also had 144,427 seats available. Most of its flights that month were on its 737-800s and MAX 8s, but the -700s were also used for some operations.
United has its operations split into mainline and regional for the first five months of the year. Mesa Airlines, one of several airlines operating on behalf of United, under the United Express brand, operated one daily flights for most of January-May. The largest aircraft United used on the route is the Airbus A321neo with 200 seats.
The first A321neo flight from Phoenix to Denver is today, and United will use the new plane through the end of the month. Although the A321neo is the largest aircraft used on the route, it offers the same number of premium seats as the Boeing 737-900ER and MAX 9s. All three of these aircraft types have 20 first class seats.
Frontier Airlines’ busiest month was September, when the carrier had 310 flights and 59,790 seats available. That month, Frontier deployed its Airbus A321neos and A320neos on the route. As Frontier’s aircraft do not yet have premium seats, the A321neo has 240 seats, an additional 40 compared to United’s A321neos.
