Insufficient ground operation performance with excessive process durations is one major contributor for flight delays caused on ground. Many European airports implemented first A-CDM but still need an automated ground process understanding and prediction system. Catching up our previous research activities we focused on explanations for turnaround process variations caused by staff skills. Therefore we analyzed the skills and the training of the ground handling staff in several steps, including a document analysis and interviews of different Ground Handlin companies within Germany. The analysis of public documents showed up a huge gap in the obligatory skills for turnaround staff. A slope of professional trained staff from airports with high traffic numbers to lower ones is also apparent. Additional we will show new findings in our research of delay impacts to process variations. As an outlook, all our efforts will approach in a complex Turnaround model predicting process duration for a satisfactory determination of the Turnaround Time and TOBT.