South African investigators are trying to determine whether the crew of the crashed Airlink British Aerospace Jetstream 41 shut down the wrong powerplant after the aircraft experienced engine failure on take-off from Durban.
Preliminary evidence from the inquiry into the 24 September accident shows that the aircraft's right-hand engine failed on rotation, following an 18s take-off roll.
But as the aircraft climbed to around 450ft above sea level, there was a power reduction of the left-hand engine. The aircraft descended and hit the ground just 50s after starting the take-off roll.
South Africa's Civil Aviation Authority says smoke had been seen emanating from the right-hand Honeywell TPE331 powerplant. But while air traffic control advised the crew of the smoke, the call came during rotation - too late to reject the take-off.
Both flight recorders have produced "good quality" data, says the CAA, and analysis is under way.
It points out that the Airlink aircraft's weight should not have prevented it from climbing on a single engine and returning to land, as certification standards require. The CAA says its inquiry will therefore concentrate on the reasons for the power reduction on the left-hand engine.
This will include analysis of human factors "such as whether the power reduction on [the left-hand engine] resulted from an incorrect identification of the failed engine, or a decision to land the aircraft as soon as possible, or other factors unknown at this time". The pilots have yet to be interviewed.
Wreckage has been transported to a hangar in Johannesburg and the powerplants are to be sent to Honeywell for strip-down and examination, to verify that the left-hand engine was functional during the flight and to determine the reason for the right-hand engine's failure.
The CAA notably says that the investigation has not turned up any evidence for grounding Jetstreams or suspending approvals granted to the carrier.
Airlink flight SA8911 had been operating as a positioning flight with only a crew of three, all of whom sustained serious injuries. The airline has acknowledged the initial findings from the CAA.
"Our training and procedural systems have worked well over the past 17 years," it says. "But in the interest of enhancing safety and preventing a similar occurrence, we have begun revisiting our human factors and other training programmes for pilots to see if there are any things we could do differently."