Why the Soviet nuclear scientists were forbidden to fly by planes

In our country, perhaps, there was no problem more important and more confidential, than the legendary Nuclear project. Not without reason special attention was paid to founders of the Soviet nuclear bomb from the authorities. Even the everyday life of scientists which was not concerning work, abounded with a set of rules. So, in September, 1948 to nuclear physicists forbade to drive cars. The confidential project As is written by Gromov Alex in the book "Stalin and Beriya Lavrenty. Confidential archives of the Kremlin", the Resolution of the State committee of defense on the beginning of practical works on creation of the Soviet nuclear bomb is dated February, 1943...