According to Official Guinness Records,
The largest banner flown by an airplane measured 218.03 m² (2,346.85 ft²) and was flown by Edmund Löbbers (Germany) in Rheine, Germany, on 10 July 2010. The aircraft used in the attempt was a Remos G3-600. Edmund flew the banner for 13 minutes. The banner weighed 19.8 kg (43.65 lbs).
For a complete list of 2010 records, please visit 2010 Guinness Records in Germany.