According to Official Guinness Records,
The largest banner flown by a helicopter measures 5,107 m² (54,971 ft²41 in²) and was achieved by Möbel Martin GmbH & Co. KG in cooparation with Martin Klenke from Helijet Charter GmbH (all Germany) in Mainz Finthen, Germany, on 18 August 2012.
For a complete list of 2012 records, please visit 2012 Guinness Records in Germany.