A week-long inquiry here into the plane crash that killed Mozambique's President suggests that pilot error was a cause of the disaster. But a key question is yet unresolved.
Why did the Soviet pilot and crew suddenly bank their Tupolev aircraft to the right late last Oct. 19 and descend for landing - well short of their destination, Maputo International Airport? Minutes later the jet slammed into a hill inside South Africa's border with Mozambique, killing nearly three dozen people, including President Samora Machel.
The Soviets and Mozambicans, who participated in a joint investigation with South Africa but declined to join this week's Johannesburg probe, charged this week that the plane had been lured astray by a decoy navigational ground-beacon. They suggested that either South Africa, or South African-allied Mozambican rebels, were responsible.
A South African aviation official told the inquiry panel - which included aviation experts from the United States and Britain - that the plane mistook an aviation beacon in nearby Swaziland for a Maputo Airport signal. The official, Roy Downes, said an on-board instrument that locks on to horizontal beacon bearings was found geared into the Swazi beacon.
Still, neither scenario seemed conclusively provable. Mr. Downes's testimony left unexplained the fact that two other instruments were locked into a frequency that matched no aviation transmitter in the area. Moscow and Maputo, for their part, put forth no concrete evidence of foul play. Maputo stressed that an abandoned camp site was found near the crash site - a finding, it said, that figured in the tripartite official report on the accident.
The Johannesburg panel's judgment of the relative probability of the ``beacon'' scenarios is likely to be key to its report.
Concerning pilot and crew performance, the panel heard evidence suggesting at least errors of omission. The thrust of testimony and questions was that, no matter what the reason for the aircraft going astray, the crew was lax in moving to correct the situation as disaster neared.
A gruesome replay of the flight's final stage - from the ``black-box'' recording of cockpit and control-tower conversation - suggested confusion as the crew looked in vain for the lights of Maputo Airport. The confusion seemed heightened by the fact that cockpit-to-tower communication had to be conducted in English, a second language to both the crew and the airport's Portuguese-speaking Mozambican officials. And the plane did not have enough fuel to make emergency flight changes.
The mystery beacon apparently convinced the crew that its instruments were malfunctioning. Some 40 seconds before the crash, the aircraft's ``ground-proximity'' alarm sounded - indicating impact ahead. But, according to testimony by South African experts, there was no sign that the crew took standard responsive action: pulling up to higher altitude to sort out the emergency. The earlier official tripartite report did cite one instrument showing a slowed rate of descent.
The head of Mozambique's own probe remarked last week that the root cause of the crash remained the unexplained beacon that drew the plane off course.
This report was written in conformity with South Africa's press restrictions.