The rules that use the category "<aircraft_activity>" are:

<contact_command_mod>

<aircraft_activity>

<contact_type-sing-neutral>

<contact_type_nom-point_id_type_none> <aircraft_activity> <contact_type-point_id_type_none-sing-simple-neutral>

<contact_type>

<contact_type_nom-point_id_type_none> <aircraft_activity> <contact_type-point_id_type_none-simple>

<contact_type-point_id_type_none>

<contact_type_nom-point_id_type_none> <aircraft_activity> <contact_type-point_id_type_none-simple>

<contact_type-pl-neutral>

<contact_type_nom-point_id_type_none> <aircraft_activity> <contact_type-point_id_type_none-pl-simple-neutral>

<contact_type-point_id_type_none-pl-neutral>

<contact_type_nom-point_id_type_none> <aircraft_activity> <contact_type-point_id_type_none-pl-simple-neutral>

<air_formation_mod>

<aircraft_activity>

<contact_type-point_id_type_none-sing-neutral>

<contact_type_nom-point_id_type_none> <aircraft_activity> <contact_type-point_id_type_none-sing-simple-neutral>