Question: Luftfahrtgesellschaft Walter started cooperating with which second-largest German airline in 2007?
Context: Luftfahrtgesellschaft Walter mbH, commonly abbreviated LGW, is a German regional airline headquartered in Dortmund.  Originally an independent provider of scheduled and chartered low-volume passenger flights, LGW started cooperating with Air Berlin in 2007, later became a full subsidiary and subsequently ceased to operate under its own name and airline code.  Today, it operates exclusively in Air Berlin's route network and corporate design. Chemische Fabrik Kalk (CFK) (lit.  Chemical Factory Kalk) was a German chemicals company based in Kalk, a city district of Cologne.  The company was founded in 1858 as "Chemische Fabrik Vorster & Grüneberg, Cöln" by Julius Vorster and Hermann Julius Grüneberg and was renamed to Chemische Fabrik Kalk GmbH in 1892.  At times the company was the second-largest German producer of soda ash and was, with almost 2400 employees, one of the largest employers in Cologne.  For decades the chimneys and the water tower of the factory dominated the skyline of Cologne-Kalk. Walter Anthony (February 13, 1872 in Stockton, CA – May 1, 1945 in Hollywood, CA) was a screenplay, titles and documentary film writer.  Before Walter started writing in films he was a dramatic and musical critic for San Francisco Morning Call. Deutsche Luft-Reederei (D.L.R.), was a German airline established in December 1917 which started operating in 1919.  The name means "German (Deutsche) Air (Luft) Shipping Company (Reederei)".  D.L.R. was reorganized as Aero Lloyd AG in 1923.  In 1926 the German government forced the airline to merge with Junkers Luftverkehr to form Deutsche Luft Hansa, the flag carrier of the Weimar Republic. David Babakhanyan (Armenian: Դավիթ Բաբախանյան , born July 2, 1975) is an Armenian film director, producer and screenwriter.  His career began in 1995, in cooperation with "Sharm Holding", as a screenwriter.  In 2003, he started cooperating with Armenia TV and in 2009 with Armenia 1 Public television of Armenia.  Since 2012, he has been the general director at Armenia TV.  He is a producer, screenwriter and director of a significant number of Armenian films and TV series. Deutsche Lufthansa AG () (] ), commonly known as Lufthansa (sometimes also as "Lufthansa German Airlines"), is the largest German airline and, when combined with its subsidiaries, also the largest airline in Europe, in terms of fleet size, and the second largest airline in terms of passengers carried during 2016.  The name of the company is derived from "Luft" 'air' and "Hansa", the Hanseatic League.  Lufthansa is one of the five founding members of Star Alliance, the world's largest airline alliance, formed in 1997. Air Berlin PLC & Co.  Luftverkehrs KG (), branded as airberlin or airberlin.com, is Germany's second-largest airline, after Lufthansa, and Europe's seventh-largest airline in terms of passengers carried.  It maintains hubs at Berlin Tegel Airport and Düsseldorf Airport and serves 12 German cities as well as destinations in Europe, the Caribbean and the Americas. Triple Alpha Luftfahrtgesellschaft (also known as 3A Airlines and 3AA) was a German airline based in Düsseldorf which has been administration since July 2011.  Their hub was at Düsseldorf Airport.  3AA operated charter, general aviation, business, cargo, flight school, air ambulance, aerial evacuation and organ transport services. This is a list of year-round and seasonal destinations served by Air Berlin, the second-largest German airline and a member of the oneworld alliance, as of September 2017.  It does not include the routes served on behalf of Eurowings. Kosova Airlines is an airline that is based in Kosovo .  The airline links Pristina to major European cities.  The airline was established in autumn 2003 by the United Nations Interim Administration Mission in Kosovo (UNMIK) and the Kosovo Government.  On 10 May 2006, the only aircraft in the Kosova Airlines fleet, a Boeing 737-700, which was wet leased from the German airline Hamburg International, was returned to that airline, and Kosova Airlines ceased operating flights.  The airline however continues to work with other airline companies flying into Pristina, such as Germanwings, LTU, Air Berlin and a few others.
Answer: Air Berlin