This scenario represents the Saur Revolution, also known as the April Revolution or April Coup.
However, I did get this from the book by Mark Urban, War in Afghanistan which don't seem to refer to it by any of those titles and simply refers to it as the coup.
The seario starts off with protests after Mir Akber Khyber is shot dead.
The president, Mohammed Daoud Khan begins to use the secret police to round up all the ring leaders of the Peoples Democratic Party of Afghanistan.
However, fail fails to arrest their most important accomplices in the army and they activate the 4th and 15 Armoured Brigades in Pol-e-Charkhi as well as the 322nd Air Regiment to the north which is equipped with MiG21 fighters.
The 4th Amoured Brigade then march on the palace which has the 1800 strong Republican Guards Brigade defending it whilst the 15th Armoured Brigade takes the airport. The MiG aircraft fly over the city and bomb the palace killing several hundred troops and straff the Central Corp HQ to deter them from joining in.