If there is no ECM that disable the SNP (TWS) mode, you have to select TWS-2 (SNP 2) in the MIG-29S, if two enemy aircrafts are at close distance each other, just lock on the nearest one, and you will notice two marks in the HUD, one is a small diamond (primary target) and the other a cross (secondary target), when the launch signal appear for both (LA1 and LA2) launch both R-77