Two Russian air force pilots died on Tuesday in a crash of one of the country\'s mainline fighter jets, army spokesmen said. Officials were blaming a technical problem in a MiG-31 interceptor for the apparent accident, which took place in the central Siberian Perm district. Russian air force command ordered all MiG-31 aircraft grounded pending determination of the exact cause of the crash. Investigators also were checking whether the pilots had violated flight instructions, Interfax reported.