Making a list of world's oldest commercial airlines is not easy. 

In a list compiled by Travel+Leisure, German airline Lufthansa was not included because its new and old airline are separate entities. Founded in 1926 and dissolved by the Allies in 1951, a completely new Lufthansa was later founded in 1953, with a resurrected name, livery and logo. 

On the other hand, Huff Daland Dusters, founded in 1924, was renamed four years later but is still the same airline which we know as Delta. 

Based on such criteria, below are the top five of the world´s oldest airlines. How many have you flown?

5. Czech Airlines

Founded on Oct. 6, 1923, in the then-Czechoslovakia  the airline uses the call sign OK. Its original name was the Czechoslovak State Airlines (CSA). 

In 1923, the airline made its maiden flight from Prague to Bratislava and grew from there until March 1939 when operations stopped until September 1945 due to World War II.

The present name Czech Airlines was used for the first time in May 1995. Six years later, the airline became a member of the SkyTeam Alliance. 

4. Aeroflot

The Russian airline, using the call sign SU, was founded on March 17, 1923.

In 1932, a name change took place: The original Dobrolyot became Aeroflot. As the flag carrier of the USSR, it was one of the world´s largest airlines during the Soviet era. 

Nowadays, it is semi-privatized because the majority of the company is owned by the Russian government. Becoming a member of the SkyTeam Alliance in 2006, Aeroflot owns 200 planes flying to more than 120 destinations. 

Read also: Qantas is named world's safest airline 2019

3. Qantas

Qantas was founded on Nov. 16, 1920, in Australia and uses the call sign QF. Its full name is Queensland and Northern Territory Aerial Services Ltd.

The airline is not only famous for its well-known logo showing a kangaroo, but also for introducing the world´s first business class aboard a Boeing 747 in 1979.

Another scorcher: Qantas is the first airline to provide non-stop flights between Australia and Europe. The service from Perth to London was launched in March aboard the new Boeing 787-9 Dreamliner.

2. Avianca

Originally named Sociedad Colombo Alemana de Transporte Aéreo (SCADTA) the airline was founded on Dec. 5, 1919, in Colombia. It uses the call sign AV.

In 1940, the company changed its name to Avianca, which is an acronym for Aerovías Nacionales de Colombia because it merged with Servicio Aéreo Colombiano (SACO) after its German backers had to divest due to World War II. 

Avianca’s maiden flight took place in September 1920 from Barranquilla to Puerto Berrio. Today, it has subsidiaries in several Latin American countries.

In 2009, the airline merged with Salvadorean carrier TACA, which was founded in 1931. Three years later it became member of the Star Alliance.

1. KLM

The world´s oldest existing airline is Koninklijke Luchtvaart Maatschappij (KLM). The English translation means Royal Aviation Company. Founded on Oct. 7, 1919, the Dutch airline uses the call sign KL. 

In 1920, Captain Jerry Shaw piloted its maiden flight from Amsterdam Schipol to London aboard a De Havilland DH-16. The airlines first transatlantic flight from Amsterdam to Curaçao took place in 1934. 

Today, the carrier boasts more than 200 planes, carrying over 30 million passengers per year. (sop/kes)