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The entire accident investigation procedure was conducted in line with the international standards and procedures (ICAO) and applicable regulations of Bosnia and Herzegovina. During the investigation, the Commission cooperated with the BiH Prosecutor's Office and the RS Ministry of Internal Affairs.

Based on the conducted investigation and analysis of the collected evidence and available information on the PIPER PA-28A plane crash, the Commission made the following conclusion:

The pilot conducted previously announced and approved flight from the Banja Luka Airport in the region of Velika Kladuša to perform veterinary vaccination from the air for the purpose of oral vaccination of foxes. The flights was conducted under the visual flight rules (VFR) and visual meteorological conditions (VMC). Take-off, flight to the area of operation, operation over the area and return to the Airport until the moment of entering the Controlled Zone (CTR) went according to plan and without any problems. The problems occurred after the plane entered the CTR of Banja Luka Airport (LQBK).

Deteriorating meteorological situation, complex air situation in the CTR zone and congestion of the frequency radio traffic led to the pilot's decision not to descend towards the centre of the CTR in instrumental meteorological conditions (IMC), in an area where the planes are not safely separated, but on its periphery or beyond to make visual contact with the ground, which was done by turning and flying towards Kozara.

Due to very poor visibility, it is assumable that, under the IMC flight conditions, the pilot had the illusion - a false sense of position in space - when there was a gradual increase in inclination and a transition to a descending turn, followed by a steep fall at an angle of about 80 degrees, with a sudden loss of altitude. It is possible that the pilot tried to avoid the cloud by turning, followed by an illusion - a false position - and a transition to a steep crash, hitting an oak tree. As a result of the impact on the tree, and then into the ground, the pilot and the vaccines machine operator were killed, causing complete destruction of the plane due to the impact and the fire following the impact.

Based on the investigation and analysis of the collected evidence and available information, the Commission concluded that the main cause of the accident was the loss of control over the plane and its fall into the wrong position caused by the uncontrolled entry of the plane into the cloud and loss of visual contact with the ground.

The plane crash was affected by:

1)    insufficient skills and experience of the pilot to fly over the mountainous terrain and under the conditions of sudden change of meteorological conditions;

2)    insufficient assessment of meteorological conditions when making a decision to fly;

3)    mental condition of the pilot caused by stress from previous flights;

4)    insufficient knowledge of the airport area and flight area;

5)    inadequate crew training planning and its implementation;

6)    loss of communication between the pilot and flight control during the flight;

7)    the pilot's decision to attempt to land under VMC conditions due to insufficient training to fly under IMC conditions;

8)    radio communication in the critical period was completely obscured by transmissions from TWR and aircraft, due to its excessive and undisciplined use;

9)    absence of crew warning on aggravating of meteorological conditions while approach to landing;

10)neglect of the aircraft controller in the CTR in the approach that failed to respond for almost 8 minutes;

11)the policy of the "STS Aviation" company to implement business plans at the cost of increased risk and reduced level of security;

12)limited possibilities to monitor the situation in the airspace/CTR under aggravated meteorological conditions;

13) absence of crew warning about aggravated meteorological situation during the plain approach.