A Mozambique Airlines captain had a "clear intention" to crash an aircraft that went down in Namibia killing 33 at the end of last month, according to a preliminary investigation.
Flight recorders showed flight TM470 crashed on November 29 while Herminio dos Santos Fernandes manipulated the Embraer 190's auto-pilot in a way which "denotes a clear intention" to bring the plane down, said Mozambican Civil Aviation Institute (IACM) head Joao Abreu.
"The reason for all these actions is unknown and the investigation continues," Abreu said.
The plane crashed in torrential rains in a swamp of Namibia's Bwabwata National Park on November 29, killing its six crew and 27 passengers.
It was flying from the Mozambican capital Maputo to Luanda in Angola.
Abreu said Dos Santos Fernandes locked himself inside the cockpit, ignored warning signals and did not allow his co-pilot back in moments before the Embraer 190 hit the ground.
"During these actions you can hear low and high-intensity alarm signals and repeated beating against the door with demands to come into the cockpit," he was quoted as saying by state news agency AIM.
The altitude was manually changed three times from 38,000 feet to 592 feet - below ground level - and the aircraft's speed was also changed manually, according to the preliminary report.
Air-brake parameters showed the spoilers, aerodynamic resistance plates on the wings, were deployed and held in that position until the end of the recordings, which proved the throttle was manually controlled.
"The plane fell with the pilot alert and the reasons which may have given rise to this behaviour are unknown. At the time, the co-pilot had left the cockpit and was absent while everything happened," Abreu said.
The black boxes retrieved from the crash site were analysed at the US National Transport Safety Board in Washington.
These indicated the aircraft was operating at normal cruising altitude, and had good communications with the control tower at Gaberone in Botswana.
The Brazilian-manufactured aircraft was the newest plane in the Mozambique Airlines fleet.
Three weeks after the incident only seven of the 33 victims have been identified. The passengers were from Mozambique, Angola, Portugal, Brazil, France and China.
Dos Santos Fernandes had 9,053 flight hours, and 1,395 as a captain. His licence was renewed in April last year and he underwent a medical examination last September.