The Soviets stated that there was an earlier ground proximity warning system (GPWS) alert about 4 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 a 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.