Complex sentence: By instructing JP550 to Squawk Stand by, Erjavec simply released a code that was allocated for the middle sector, the DC-9 would now lose the data tag on his screen and become a paint among many others.
Split into simpler sentences: By instructing JP550 to squawk Standby, Erjavec simply released a code allocated for the middle sector. The data tag for the DC-9 would now disappear from his screen and the aircraft would become merely a point among many others.