Refer to figure.
LOKH (Friesach/Hirt) lies outside controlled airspace, but LOWK (Klagenfurt) lies inside Class D CTR (Control Zone), as indicated by the solid blue lines surrounding it and the label: "CTR KLAGENFURT D 7000 FT MSL / 1000 FT AGL".

Entry into Class D airspace under VFR requires two-way radio communication and a clearance, and also an ATC flight plan.

According to the ICAO Annex 2, regarding the flight plans:

1. A flight plan shall be submitted prior to operating:
   a) any flight or portion thereof to be provided with air traffic control service,
   b) any IFR flight within advisory airspace,
   c) any flight within or into designated areas, or along designated routes, when so required by the appropriate ATS authority to facilitate the provision of flight information, alerting and search and rescue services,
   d) any flight within or into designated areas, or along designated routes, when so required by the appropriate ATS authority to facilitate coordination with appropriate military units or with air traffic services units in adjacent States in order to avoid the possible need for interception for the purpose of identification,
   e) any flight across international borders.
2. A flight plan shall be submitted, before departure, to an air traffic services reporting office or, during flight, transmitted to the appropriate air traffic services unit or air-ground control radio station, unless arrangements have been made for submission of repetitive flight plans.

Note: Class D is provided with Air Traffic Control Service.