During two field measurement campaigns aircraft wake vortex trajectory and wind measurement data have been collected at Frankfurt airport. Three different approaches to analyse the data have been used in order to estimate crosswind threshold values supporting vortex-free corridors for departing aircraft. Although several competing effects as wake vortex transport in and out of ground effect, temporal and spatial wind variability, and the spreading of aircraft trajectories after take-off complicate the analyses, all three approaches lead to similar crosswind thresholds. Employing standard instrumentation at 10 m height a minimum crosswind threshold of 3.5 – 4.6 ms-1 has been identified to clear a safety corridor of 150 m width from wake vortices with a 95% probability within 60 seconds. Alternative estimations of crosswind thresholds employing different instrumentation and different height ranges are reported. Crosswind thresholds can be reduced if the wind is measured close to the air mass in which the vortices evolve. A definite crosswind threshold for operational use cannot be deduced solely from this study since critical factors like risk and safety assessment have not yet been taken into account.