Licenses for the provision of air transport and the operation of civilian airports can only be granted to companies that are owned at least 51% and controlled, directly and indirectly by EU/EEA Member States or EU/EEA nationals.
"Chapter Four - AIRPORTS
Article 43
(2) (Amended, SG No. 85/1998) Civilian airports shall encompass:
1. (amended, SG No. 81/2011) airports for public use for the provision of international and domestic carriage services, commercial operations by aircraft and other services in return for payment;
2. (amended, SG No. 34/2001, SG No. 52/2004, SG No. 81/2011) airports serving flights performed for the provision of commercial aviation service inclusive of one-off air carriage flights involving aircraft with maximum take-off mass of up to 5,700 kg, or with a passenger capacity of up to 19 seats;
[...]
Article 43b 
(1) Civilian airports for public use which constitute State property shall be used under the terms established by this Act by airport-operator merchants who have been awarded a works concession or a services concession according to the procedure established by the Concession Act or by commercial corporations wherein the State is the sole owner of the capital.
(2) A services concession may furthermore be granted according to the procedure established by the Concessions Act and under the terms established by this Act to civil airports for public use constituting State property for:
1. passenger handling and/or freight, baggage and mail handling, and/or carrying out an accessory activity in a self-contained part of an airport designated by an effective master plan for the development of the airport, and/or
2. a service provided within the perimeter of the airport, other than the groundhandling activities referred to in Article 48e (3). [...]
(4) The concessionaire selection procedure for a concession referred to in Paragraph (1), the requirement for an airport operator referred to in Items 2 and 3 of Article 48d (2) shall be established as a condition for participation in the procedure. By the tenders thereof, the participants in the procedure shall submit proposals regarding the organisation, equipment and technology whereby they will ensure conformity to the established standards and procedures for ensuring flight safety and security at the airport concerned, as well as proposals regarding the manner of management and operation of the airport. An airport operator licence shall be issued to the concessionaire after the conclusion of the concession contract within the time limits agreed therein where the concessionaire meets the requirements for the issuing of a licence, as defined by this Act.
[...]
Art. 43f.
(1) Natural or legal persons registered as merchants, who use or have investment initiative for building or enlargement of a civil airport for public use, apart from the cases of civil airports for public use – public state property or municipal property, shall submit an application to Chief Directorate "Civil Aviation Administration". 
[...]
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Article 48c
(New, SG No. 85/1998, amended, SG No. 34/2001, SG No. 52/2004)
(1) (Supplemented, SG No. 10/2007) The activities of management and operation of a civil airport under art. 43, para 2, item 1 and 2 shall be carried out by entrepreneurs registered under the Commerce Act or persons registered as traders under a legislation of an European Union Member State or of another country – a party to the Agreement on the European Economic Area, to whom a licence for airport operator has been issued. 
[...]
Article 48d 
(1) An airport operator's license shall be issued to attest to the fact that the organization, technical equipment, technology and personnel of the licensed entity comply with the standards and requirements of safe and reliable maintenance of the airport operability.
(2) An airport operator's license shall be issued subject to condition that:
1. the applicant has procured a valid certificate of airport operability;
2. the applicant has presented proof of financialstability;
3. the airport manpower have the qualifications, professional experience, and length of service requisite to conduct this business;
[...]
Article 48e
(New, SG No. 34/2001, amended, SG No. 52/2004)
(1) (Supplemented, SG No. 10/2007) Any activities pertinent to the ground service of a civilian airport as per Article 43 (2) items 1 and 2 shall be performed by commercial entities registered as per the Commercial Act or persons registered as merchants under the legislation of an European Union member state or another country signatory to the European Economic Area Agreement to which a ground service operator's license has been duly issued.[...]
(3) A ground service operator's license shall be granted in respect of each of the activities to be performed at the respective airport:
1. ground administration and supervision; 2. passenger service;3. luggage processing; 4. cargo and mail processing; 5. dock service of aircraft; 6. general service of aircraft; 7. provision of aircraft with fuel and lubricants; 8. technical servicing of aircraft; 9. flight operation and crew administration; 10. ground transportation; 11. on-board catering.
[...]
Chapter Five - FLIGHTS [...]
Article 64
(Amended, SG No. 85/1998)
(1) (Amended, SG No. 52/2004, supplemented, SG No. 10/2007, amended, SG No. 66/2008, effective 25.07.2008) An aircraft operator is an entity registered pursuant to the Commerce Act or registered as a merchant under the legislation of an European Union member state or another country signatory to the European Economic Area Agreement, in possession of an aircraft operator's certificate attesting to the fact that the operator has the professional competence and logistical capacity to ensure the safe operation of aircraft in the performance of the air navigation activities listed in the said licence.
(2) (New, SG No. 66/2008, effective 25.07.2008) The right to perform specialized aviation operations, other than commercial air carriage, shall be evidenced by an aircraft operator's license for the performance of specialized aviation operations. An aircraft operator performing specialized aviation operations shall be an entity registered under the Commerce Act or registered as a merchant under the relevant legislation of a European Union member state, or another country signatory to the European Economic Area Agreement. [...]" (Civil Aviation Act, State Gazette No. 94/1.12.1972, as amended)
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"CHAPTER II - OPERATING LICENCE
Article 3 - Operating licence
1.   No undertaking established in the Community shall be permitted to carry by air passengers, mail and/or cargo for remuneration and/or hire unless it has been granted the appropriate operating licence.
2.   The competent licensing authority shall not grant operating licences or maintain them in force where any of the requirements of this Chapter are not complied with.
[...]
Article 4 - Conditions for granting an operating licence
An undertaking shall be granted an operating licence by the competent licensing authority of a Member State provided that:
(a) its principal place of business is located in that Member State;
(b) it holds a valid AOC issued by a national authority of the same Member State whose competent licensing authority is responsible for granting, refusing, revoking or suspending the operating licence of the Community air carrier;
(c) it has one or more aircraft at its disposal through ownership or a dry lease agreement;
(d) its main occupation is to operate air services in isolation or combined with any other commercial operation of aircraft or the repair and maintenance of aircraft;
(e) its company structure allows the competent licensing authority to implement the provisions of this Chapter;
(f) Member States and/or nationals of Member States own more than 50 % of the undertaking and effectively control it, whether directly or indirectly through one or more intermediate undertakings, except as provided for in an agreement with a third country to which the Community is a party; [...]" (Regulation (EC) No 1008/2008 of the European Parliament and of the Council on common rules for the operation of air services in the Community) 
Civil Aviation Act, State Gazette No. 94/1.12.1972, as amended
Regulation (EC) No 1008/2008 of the European Parliament and of the Council.
[<a href="https://www.minfin.bg/upload/38252/Civil_Aviation_Act.pdf">Act</a>],[<a href="https://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1457094596807&uri=CELEX:32008R1008">Regulation</a>]