World's top 10 busiest routes by number of flights in 2021. All of the top 10 routes were domestic, and most were in Asia. 

1. Jeju to Seoul Gimpo, South Korea

Frequency 2021: 85,880 flights

Frequency Change vs 2019: +0.30%

Major Airlines: Korean Air, Asiana Airlines, Jeju Air, T'way Air

Despite another year full of uncertainty amid the COVID-19 pandemic, the domestic route between Jeju and Seoul Gimpo, often known as the ‘Hawaii of South Korea', maintained its position for consecutive years. The 450-km domestic route is popular among leisure travellers, and around 235 flights were operated each day in 2021.

Nine carriers competed in the GMP-CJU market in 2021, led by Korean Air which offered about 4 million two-way seats. A further 3.9 million were available onboard Asiana Airlines, while Jeju Airlines provided 2.9 million seats.

In total, capacity between the destinations was almost 17.1 million seats—down by just 1.9% on the figure offered in 2019.

Most of the flights were operated by Boeing 737s and Airbus A320 family jets, together with the A220 with Korean Air. Hi Air's ATR-72s operated the only turboprop flight. Almost one-quarter of the flights were operated by Korean Air Airbus A330 and Asiana Boeing 767 widebodies.  

2. Seoul Gimpo to Busan, South Korea 

Frequency 2021: 34,897 flights

Frequency Change vs 2019: +64%

Major Airlines: Air Busan, Korean Air, Air Seoul

The second busiest route is another South Korean domestic route between Seoul Gimpo and Busan. The flight frequency was increased by a staggering 65% compared to 2019. More than 90 flights were operated each day between the airports in 2021. The market was highly dominated by Airbus A320 family jets and Boeing 737s, with a handful of flights operated by Korean A220s.

Seoul to Busan saw a significant boost in frequency amid the pandemic as air transport was chosen as the safest and quickest means of transport. The newest observatory in Busan, Busan X The Sky and the Osiria Tourist Complex in Gijang-gun further boosted leisure travel, hugely boosting the flight frequency.

3. Jeddah to Riyadh, Saudi Arabia

Frequency 2021: 32,405 flights

Frequency Change vs 2019: -14.80%

Major Airlines: Saudia, Flyadeal, Flynas

Saudi Arabian domestic route between King Abdulaziz International Airport, Jeddah and King Khalid International Airport, Riyadh ranked the third busiest route in 2021.

Aircraft types on this route range from the Airbus A320 family jets to Boeing 737s. Saudia used Airbus A330 and Boeing 787 Dreamliner widebodies regularly on flights between the two cities.

4. Fukuoka to Tokyo Haneda, Japan

Frequency 2021: 32,400 flights

Frequency Change vs 2019: -18.8%

Major Airlines: ANA, Japan Airlines, Skymark Airlines, StarFlyer

Japan's domestic route from Fukuoka to Tokyo Haneda has been consistently being one of the world’s busiest routes in both number of passengers and number of flights.

Many aircraft ranging from Airbus and Boeing narrowbodies to widebodies were used on this route. Along with Boeing 737s, Japan Airlines used Airbus A350s, Boeing 777s and 787s. ANA also operated a mix of narrowbodies and Boeing 767, 787 widebodies.

5. Sapporo New Chitose to Tokyo Haneda, Japan

Frequency 2021: 31,495 flights

Frequency Change vs 2019: -20.3%

Major Airlines: ANA, Japan Airlines, Air Do, Skymark Airlines

Rounding up the top five is another Japanese route between Sapporo and Tokyo Haneda. The fastest means of transport between the largest city of Japan's northernmost island of Hokkaido and Tokyo is by air. More than 85 daily flights were operated between the cities in 2021.

The majority of the flights were operated by ANA and Japan Airlines, operating a mix of narrowbody and widebody jets. Japan Airlines operated most of the flights using Airbus A350, Boeing 767 and 777 widebodies, whereas ANA used Boeing 767 and 787s on this route along with narrowbody aircraft.

6. Hanoi to Ho Chi Minh City, Vietnam

Frequency 2021: 29,347 flights

Frequency Change vs 2019: -38.2%

Major Airlines: Bamboo Airways, Vietnam Airlines, Vietjet Air

The Vietnamese domestic route between Hanoi and Ho Chi Minh City is the sixth busiest route in 2021. Although flight frequencies plunged by 38.2%, almost 80 flights were operated daily in 2021.

Both narrow and widebody jets served the high-demand route between Hanoi and Ho Chi Minh City. Bamboo Airways and Vietnam Airlines operated around one-quarter of the flights using Boeing 787 Dreamliners, whereas other flights were operated by narrowbody jets. Vietnam Airlines also used Airbus A350s on some flights. 

7. Shanghai Hongqiao to Shenzhen, China 

Frequency 2021: 29,250 flights

Frequency Change vs 2019: -2.0%

Major Airlines: China Eastern, China Southern, Shenzen Airlines, etc.

The Chinese route between Shanghai Hongqiao and Shenzhen was the seventh busiest route in 2021. As many as seven Chinese airlines such as China Southern, China Eastern, and Spring Airlines operate flights between the two cities.

While most of the airlines used Airbus and Boeing narrowbodies to operate this route, China Eastern heavily used Airbus A330s to ensure high seats per flight. Widebodies were used by other airlines on multiple occasions.

8. Beijing Capital to Shanghai Hongqiao, China

Frequency 2021: 28,120 flights

Frequency Change vs 2019: -5.5%

Major Airlines: Air China, Hainan Airlines, China Eastern

Shanghai Hongqiao Airport mainly serves domestic and regional flights and hosts another busiest route globally. Three major Chinese airlines operated equivalent to 77 daily flights in 2021.

Many aircraft were used on this route, with China Eastern Airlines and Air China operating the most diverse fleet of Airbus A330, A350, Boeing 777, and narrowbody jets. Besides narrowbodies, China Southern used Airbus A330s on some of the flights.

9. Cancun to Mexico City, Mexico

Frequency 2021: 27,228 flights

Frequency Change vs 2019: -14.0%

Major Airlines: Aeromexico, Viva Aerobus, Volaris

Over to North America, the route between Cancun and Mexico City was the busiest American route in 2021, with over 70 daily flights. This route is heavily dependent on Airbus A320 family jets and Boeing 737s.

10. Jakarta to Denpasar-Bali, Indonesia

Frequency 2021: 26,959 flights

Frequency Change vs 2019: -9.10%

Major Airlines: Garuda Indonesia, Batik Air, Lion Air, Citilink

Indonesia's domestic route between Jakarta and Bali was the tenth busiest route in 2021. While the Boeing 737 and Airbus A320 were common on the market, Garuda Indonesia deployed A330 and Boeing 777 on the route. Standing out among others, Citilink's ATR-72s flight was the only turboprop flight in operation.

Top 50 busiest routes in the world in 2021 by flight frequency: Source OAG Schedules Analyser

RankAirport pairFrequenciesChange vs 2019
1Jeju (CJU)South KoreaSeoul Gimpo (GMP)South Korea858800.3%
2Seoul Gimpo (GMP)South KoreaBusan (PUS)South Korea3489764.0%
3Jeddah (JED)Saudi ArabiaRiyadh King Khalid (RUH)Saudi Arabia32405-14.8%
4Fukuoka (FUK)JapanTokyo Haneda (HND)Japan32400-18.8%
5Sapporo New Chitose (CTS)JapanTokyo Haneda (HND)Japan31495-20.3%
6Hanoi (HAN)VietnamHo Chi Minh City (SGN)Vietnam29347-38.2%
7Shanghai Hongqiao (SHA)ChinaShenzhen (SZX)China29250-2.0%
8Beijing Capital (PEK)ChinaShanghai Hongqiao (SHA)China28120-5.5%
9Cancun (CUN)MexicoMexico City Juarez (MEX)Mexico27228-14.0%
10Jakarta (CGK)IndonesiaDenpasar-Bali (DPS)Indonesia26959-9.1%
11Mumbai (BOM)IndiaDelhi (DEL)India26738-40.5%
12Dar Es Salaam (DAR)TanzaniaZanzibar (ZNZ)Tanzania262010.5%
13Guangzhou (CAN)ChinaChengdu (CTU)China26123-0.6%
14Cape Town (CPT)South AfricaJohannesburg (JNB)South Africa24674-30.0%
15Bogota (BOG)ColombiaCartagena (CTG)Colombia22094-33.1%
16Jeju (CJU)South KoreaBusan (PUS)South Korea21962-0.4%
17Belize City Goldson (BZE)BelizeDangriga (DGA)Belize21895-9.0%
18Jakarta (CGK)IndonesiaMedan Kuala Namu (KNO)Indonesia217224.3%
19Melbourne (MEL)AustraliaSydney Kingsford Smith (SYD)Australia20674-62.1%
20Chengdu (CTU)ChinaBeijing Capital (PEK)China20542-16.4%
21Guangzhou (CAN)ChinaHangzhou (HGH)China204263.8%
22Tokyo Haneda (HND)JapanOsaka (Itami) (ITM)Japan20347-9.7%
23St Barthelemy (SBH)Saint BarthelemySt Maarten (SXM)St Maarten (dutch Part)20216-22.2%
24Guangzhou (CAN)ChinaShanghai Hongqiao (SHA)China19957-2.5%
25Jakarta (CGK)IndonesiaSurabaya (SUB)Indonesia19734-39.6%
26Jakarta (CGK)IndonesiaMakassar (UPG)Indonesia19690-43.3%
27Chongqing (CKG)ChinaShenzhen (SZX)China1921611.6%
28Los Angeles (LAX)USSan Francisco (SFO)US19211-42.3%
29Bengaluru (BLR)IndiaDelhi (DEL)India19011-31.2%
30Chengdu (CTU)ChinaShenzhen (SZX)China18627-0.1%
31Tokyo Haneda (HND)JapanOkinawa Naha (OKA)Japan18255-16.5%
32Hangzhou (HGH)ChinaShenzhen (SZX)China17739-1.2%
33Belize City Goldson (BZE)BelizePlacencia (PLJ)Belize176539.7%
34Bogota (BOG)ColombiaMedellin (MDE)Colombia17643-25.4%
35Las Vegas (LAS)USLos Angeles (LAX)US17443-33.1%
36Cheongju (CJJ)South KoreaJeju (CJU)South Korea1722016.0%
37Sao Paulo Congonhas (CGH)BrazilRio de Janeiro Santos Dumont (SDU)Brazil17200-53.4%
38Durban King Shaka (DUR)South AfricaJohannesburg (JNB)South Africa16830-33.4%
39Honolulu (HNL)USKahului (OGG)US16487-32.7%
40Mexico City Juarez (MEX)MexicoMonterrey (MTY)Mexico16203-42.3%
41Bogota (BOG)ColombiaCali (CLO)Colombia16160-23.9%
42Jinghong (JHG)ChinaKunming (KMG)China16122-24.7%
43Delhi (DEL)IndiaSrinagar (SXR)India1604154.3%
44Mashhad (MHD)IranTehran Mehrabad (THR)Iran15639-8.0%
45Beijing Capital (PEK)ChinaShenzhen (SZX)China15551-34.5%
46Abuja (ABV)NigeriaLagos (LOS)Nigeria155193.5%
47Guadalajara (GDL)MexicoMexico City Juarez (MEX)Mexico15153-43.9%
48Belize City Goldson (BZE)BelizeSan Pedro (SPR)Belize151171.6%
49Portland (PDX)USSeattle-Tacoma (SEA)US15086-24.5%
50Kolkata (CCU)IndiaDelhi (DEL)India15025-27.5%

Sources:  Routes Online and OAG