What measures were taken to keep Soviet airline pilots in the Soviet Union?
Civilian pilots had a quite comfortable life. Flying high-tech gear has an attraction in itself, and the propaganda did what it could to strengthen patriotic spirits. There were not many reasons to defect if you did not mind the nonsense in the papers but appreciated to be part of a privileged class. And everybody knew that defection would have dire consequences for all relatives left behind.

The same is true for military pilots, and on top the Russian air defense was organized quite differently from NATO's, thus military pilots flew almost by remote control. This went as far as using radios which had only a dozen of pre-set frequencies. The pilots did not know the frequency, they just pushed the button with the number they were told by ground control.