Ukrainian investigators have belatedly detailed the deceleration and stall of a heavy Antonov An-24RV which fatally crashed as it attempted to land at Donetsk six years ago.
Investigation authority NBAAI has published the findings of the inquiry showing that the aircraft had departed Odessa with a take-off weight of almost 23.4t – which meant it was nearly 1.6t overweight.
The 40-year old South Airlines aircraft (UR-WRA) was transporting 44 passengers, football supporters on a charter flight.
Visibility at Donetsk had been reduced by fog at the time of the approach, in darkness, to runway 08.
At the decision height, says the inquiry, the captain was unable to see the approach lights of the runway and – without informing the crew – began to reduce the descent rate.
Flight-data recorder information shows that the aircraft had reached an inner marker radio beacon, located 1,000m from the runway, and was descending through 80m when the captain pulled on the control column.
This caused the aircraft's airspeed to decline to 107kt.
"The [crew] did not take timely action to maintain the aircraft's airspeed by increasing the engine power," says the NBAAI.
It adds that the pilots had not calculated, before the approach, the An-24's landing weight to determine whether to use the auxiliary power unit.
Activation of the APU is compulsory if the landing weight is above 21.7t. The inquiry says the aircraft was operating at nearly 280kg above this threshold, and the APU should have been switched on.
This high landing weight combined with operation of the engine anti-icing system, says the inquiry, meant the captain's pulling the control column contributed to the airspeed's falling to a "catastrophic" level of around 75kt.
The unstable aircraft suddenly rolled 12° to the left, then 58° to the right, before rolling 18° left and then 49° right.
At this extreme bank angle the right wing struck the ground and partly broke away, and the aircraft slid before coming to rest 50m from a concrete airport boundary with its fuselage fractured. This enabled some passengers to evacuate.
The inquiry says the captain's decision simply to halt the descent at the decision height illustrates "poor training" and an inability to act quickly and correctly in difficult circumstances.
Five fatalities resulted from the accident, with another eight occupants receiving serious injuries.
Ukrainian authorities had previously indicated that the aircraft had been carrying unregistered passengers, adding that crew was not approved to operate the flight under the weather conditions present and should have been flying with instructor support.