Flight Kassel - Istanbul prices from €337.17

Aegean Airlines is the largest airline in Greece, operating both domestic and international flights to over 150 destinations. Founded in 1987, the airline has grown to become a major player in the European aviation market, with a fleet of over 60 aircraft and a reputation for high-quality service. Aegean Airlines is a member of the Star Alliance, a global airline network that includes some of the world's largest carriers. The airline has won numerous awards for its customer service, including the Skytrax award for Best Regional Airline in Europe for nine consecutive years.

Air Europa is a Spanish airline that was founded in 1986. It is a member of the SkyTeam alliance and operates flights to over 50 destinations across Europe, the Americas, Africa, and Asia. The airline's main hub is located at Adolfo Suárez Madrid–Barajas Airport, and it also has secondary hubs at Palma de Mallorca Airport and Tenerife North Airport. Air Europa operates a fleet of over 50 aircraft, including Boeing 787 Dreamliners, Airbus A330s, and Embraer E195s. The airline offers a range of services to its passengers, including in-flight entertainment, Wi-Fi, and a loyalty program called SUMA.

Onur Air is a Turkish low-cost airline that was founded in 1992. It operates scheduled domestic and international flights to various destinations in Europe, Asia, and Africa. The airline's main hub is located at Istanbul Atatürk Airport, and it also has secondary hubs at Antalya Airport and İzmir Adnan Menderes Airport. Onur Air operates a fleet of Airbus A320 and A321 aircraft, and it offers a range of services to its passengers, including in-flight entertainment, meals, and beverages. The airline has faced some safety concerns in the past, but it has since improved its safety record and continues to operate as a popular budget airline in Turkey.

Pegasus Airlines is a low-cost airline based in Turkey. It was founded in 1990 and began operations in 2005. The airline operates flights to over 100 destinations in 40 countries, primarily in Europe, the Middle East, and Asia. Pegasus Airlines has a fleet of over 80 aircraft, consisting of Airbus A320s and Boeing 737s. The airline offers a range of services, including online check-in, in-flight meals, and a loyalty program. Pegasus Airlines is known for its affordable fares and has won several awards for its customer service and operational efficiency.

Turkish Airlines is the national flag carrier airline of Turkey, headquartered in Istanbul. It operates scheduled flights to over 300 destinations in Europe, Asia, Africa, and the Americas, making it one of the largest airlines in the world by number of destinations served. Turkish Airlines has won numerous awards for its service, including "Best Airline in Europe" six years in a row from 2011 to 2016. The airline operates a modern fleet of over 350 aircraft, including Airbus A320s, A330s, A340s, A350s, and Boeing 737s, 777s, and 787s. Turkish Airlines is a member of the Star Alliance, the world's largest airline alliance.

Ukraine International Airlines (UIA) is the flag carrier airline of Ukraine, headquartered in Kyiv. It was founded in 1992 and operates scheduled and charter flights to over 80 destinations in Europe, Asia, Africa, and the Americas. The airline's fleet consists of Boeing and Embraer aircraft, and it offers both economy and business class seating options. UIA is a member of the International Air Transport Association (IATA) and the Association of European Airlines (AEA). The airline has won several awards for its services, including the Skytrax World Airline Awards for Best Airline in Ukraine and Best Business Class in Ukraine.