Little if any documentation of the details behind the cause of the crash has been released. The investigation into the matter was quickly placed under wraps. What is certain is that the plane in question had just come out of an extensive overhaul that took months to finish. An irresponsible technical error was made during the overhaul: the cables for the ailerons were incorrectly connected (left cable to right aileron and vice versa). Thus, when the pilots tried to straighten the plane, they ended up tilting it further, resulting in a crash at an extremely low altitude during take-off. According to an official report (made public only in 2001, and thanks to the efforts of a journalist from the Bulgarian newspaper "24 hours"), lack of expertise was said to be the culprit - the procedure was carried out by technicians lacking practical experience and using two separate design plans.