FRANKFURT (dpa-AFX) - Warning strikes at several German airports on Friday also affected operations at Frankfurt Airport. "We have a higher passenger volume, so there are slightly longer waiting times," a Fraport spokesman said. Several thousand additional passengers were estimated to have flown through Frankfurt, he added. At the airports in Düsseldorf, Cologne/Bonn and Stuttgart, around 580 flights were canceled on Friday following the strike call by the Verdi trade union. The background to the strike is negotiations on pay in the aviation security industry and the wage dispute in the public sector./mrr/DP/mis