Discounting the possibility of a false VOR beacon, an analysis of which was included in an appendix, the board considered it probable that the flight crew had inadvertently set the first of two VOR receivers on board to the Matsapa VOR frequency. This error was made more likely by the poor design of the instruments, the absence of back lighting of the selected frequencies, the fact the two frequencies were unusually close, 112.7 MHz for Maputo and 112.3 MHz for Matsapa, and the similarity between the figures '7' and '3' on the Soviet instrumentation.