What you want is a radio call, not an action. That's why addAction isn't working for you.
Radio calls are done with triggers. In the condition portion, one of the items is a drop-down menu, from which you may select Radio Alpha, Radio Bravo, Radio Charlie, and so on. Choose one of those. Put the flyInHeight command in the trigger's On Activation field.
When you test the mission, by making the appropriate radio call, the code will be executed.
As far as I know, only a group leader may make radio calls, so it will not be available to all, unless every player is a group leader.