June 12 (Reuters) - The Biden administration on Monday added 43 entities to an export control list, including Frontier Services Group Ltd, a security and aviation company previously run by Erik Prince, for training Chinese military pilots and other activities that threaten U.S. national security. The Test Flying Academy of South Africa, a flight school under scrutiny by authorities in Britain for recruiting British ex-military pilots to train Chinese military fliers, was also added to the U.S. Commerce Department's Entity List. Companies on the list are restricted from receiving U.S. exports for activities deemed contrary to U.S. interests. The new...