On site On scene the South African police located and took custody of the cockpit voice recorder (CVR) and flight data recorder (FDR) (the aircraft was equipped with both digital and magnetic FDRs). On arrival, Mozambican minister Sérgio Vieira asked for the documents that were taken from the aircraft to be handed to him. The SA commissioner of police,
Johann Coetzee, had already made copies of these, and the documents were transferred to Vieira. In accordance with the South African Air Control Act, aircraft accidents are required to be investigated by the SA Department of Transport. Thus, Pik Botha consulted Hendrik Schoeman of the Department of Transport, once Machel's death was confirmed. After Botha and Schoeman had visited the crash site, Botha cited special circumstances and other international
protocols as reasons to become involved. The three international teams signed a protocol of secrecy on 14 November 1986 Board members participated in the earlier fact-finding portion of the investigation, and conducted public hearings at the
Supreme Court in
Johannesburg from 20 January until 26 January 1987. The board then adjourned to analyze the evidence and reach conclusions as to cause. The Mozambican team provided 11 pages of suggested corrections to the draft, some of which were adopted by the Board. In their submission, the Mozambican delegation stated that according to the survivors the
South African Police searched the aircraft for documents rather than tending to the injured passengers. Mozambique also provided a technical report prepared by
Ron Chippindale of the New Zealand Office of Air Accidents Investigations examining the possibility of tampering with or replacing the genuine Maputo VOR signal with a decoy. His conclusions were that it would be "simple" to set up a mobile VOR. However, in order to effectively replace the genuine signal, the Maputo VOR would have to be turned off. The Mozambican analysis of and findings from the evidence led them to conclude: • The accident resulted from a critical situation which originated from the right turn away from the planned route. • No explanation for the deviation was agreed upon by the three countries, and there was new evidence from the USSR that the aircraft turned to follow a false signal. • The discrepancies from procedure of the Maputo controller and flight crew were not the main causes of the accident. • The investigation should be continued in order to determine the origin of the VOR signal.
Soviet submission The Soviet Union, the state of manufacture of the aircraft, was given a draft of the final report and a chance to review and submit comments in accordance with
ICAO convention. In their remarks, the Soviet Union reiterated their endorsement of the previously agreed upon factual information contained in the draft. However, regarding the analysis, conclusions and recommendations that followed, the Soviets stated the basic task of the investigation should be to determine the reasons for the 37° turn, which "remained unsolved in the report", and that conclusions of the draft based on the crew's errors were "totally ungrounded". They ended their remarks with a full rejection of the draft, calling it "worthless", and instead offering their own analysis and conclusions. The Soviet delegation stated the theory that the crew had mistakenly selected the Matsapa VOR was contradicted by the known settings of the onboard navigation equipment and the timing of the turn. They said that the data recovered from the magnetic flight data recorder did not correspond to the path of an aircraft following the signal from the Matsapa VOR. The Soviet team submitted a technical report to support their belief the Matsapa VOR's signal was not strong enough at the point of the turn for the navigation equipment on board the aircraft to receive it effectively, and further that the flight was below the coverage of the VOR, meaning that the signal from the Matsapa VOR could not have been the cause of the deviation. According to the Soviets, the other navigational aids at Maputo were not strong enough to reach the aircraft and were of no help to the flight crew. A
LAM Airlines Boeing 737 flying at around the same time as the accident aircraft reported receiving the Maputo VOR signal unusually early, at a distance of about . The Soviets stated that this was actually the false decoy beacon that was working with a higher signal level that the actual Maputo VOR. The Soviets stated that there was an earlier
ground proximity warning system (GPWS) alert about minutes before impact which was triggered by the signal from the decoy VOR beacon, and this false alert was interpreted by the flight crew as a systems fault in the GPWS. Receipt by the flight crew of the visual landing clearance from the Maputo controller implied permission to descend below according to ICAO procedures. When the GPWS sounded shortly before impact the crew, doubting its reliability, disregarded it as false, and believing they were over the low terrain continued their descent. • The aircraft's equipment performed with the required accuracy for a safe flight. • The crew's qualifications and experience excluded the possibility that the deviation off course was as result of unpreparedness or unattentiveness. The crew were efficient in monitoring the aircraft and maintaining contact with the Maputo air traffic controller up until the moment of impact. • The crew and controller were prepared for an ILS approach to runway 23, however away from Maputo the aircraft turned 37° to the right. This turn was a result of a false VOR signal situated beyond the limit of Maputo airport, and resulted in the aeroplane being led into hilly ground and its collision with terrain. This signal, also received by a LAM Airlines Boeing 737, was the result of a premeditated action. • The weather conditions along the route, at Maputo airport and at the alternative airport did not hamper the flight and was not a cause of the outcome. ==Conspiracy theories and subsequent investigations==