Half Life : Source apache can't be spawned

The Apache attack chopper from Half Life 1/Source can’t be spawned in game.

In the map C2A5, you normally encounter a Apache helicopter and it shoots at you. But instead of that, it spits out a error in the console. Before i got to this map, i added the Apache chopper ( monster_apache ) in the Half Life Source NPCs list, but it’s the same ol’ error.

Was it removed in a earlier version of GMod, or was it just left out altogether?

Attempted to create unknown entity monster_apache!

It was never added by Garry. You could make a request here but it’ll be a while.