According to Official Guinness Records,
The most countries visited by fixed wing aircraft in 24 hrs is 11 and was achieved by James van der Hoorn and Iain Macleod (both UK) in their Piper PA28 aircraft on 9 August 2010. The pair departed from Krakow, Poland and stopped at the following airports on their way home to Southend, UK: Brno Turany, Czech Republic;Bratislava, Slovakia;Gyor Per, Hungary;Krems Langenlois, Austria;Vilshofen, Germany;St Gallen, Switzerland;Haguenau, France;Noertrange, Luxembourg;Limburg Regional, Belgium;Maastricht Aachen, Netherlands.
For a complete list of 2010 records, please visit 2010 Guinness Records in United Kingdom.