On April 13, 14, and 17, NATO fighters were deployed to intercept Russian reconnaissance aircraft Il-20. The aircraft were flying with their transponders turned off and without flight plans, not maintaining radio contact with the Regional Air Traffic Control Center. On April 13, a military transport aircraft An-26 was also identified. It was flying without a flight plan but with its transponder on and maintained communication with the controllers. On April 15, fighters were scrambled to intercept two multipurpose Su-30SM fighters. These aircraft were also flying with their transponders turned off, without flight plans, and did not communicate with the control center.