South African investigators have revealed that the crew of a Convair 340 were unsure which of the aircraft's two engines had caught fire before it crashed while attempting to return to Wonderboom airport.

Inquiries into the fatal accident also found that no effort was made to carry out the standard emergency procedures to deal with the fire.

The aircraft (ZS-BRV) took off from Wonderboom on a scenic flight, carrying two crew and 17 passengers – one an engineer on the jump seat – on 10 July last year.

Investigators found that undetected damage and substandard maintenance involving engine cylinders had resulted in a manifold pressure defect. Manifold pressure fluctuations were observed as the aircraft reached 50kt and the inquiry says the crew should have aborted the take-off.

As the Convair rotated its left-hand Pratt & Whitney R-2800-CB16 radial engine caught fire.

Video evidence from the cockpit shows that one of the passengers, the engineer's assistant, left their seat to inform the crew of the left-hand engine situation before returning to the cabin.

But the South African Civil Aviation Authority inquiry states that, despite being told, the crew was "still not sure which engine was on fire".

None of the emergency procedures, such as feathering the propeller or shutting down the engine, were followed. The cockpit video showed the left engine's rpm indicator was fluctuating, followed by illumination of the left engine's fire warning light and an aural alarm.

"At no stage did the crew discuss or attempt to extinguish the fire in the left engine," the inquiry says. The extinguishing system was not activated and the engine remained operating and burning throughout the flight.

The Convair had climbed to 800ft after take-off before turning right as the crew declared an emergency and sought to return to the airport.

"At this stage, the crew were just observing the [engineer] who was continuously operating the engine controls and overhead panel switches," says the inquiry, citing the video evidence, despite the engineer's not being rated as a pilot on the aircraft.

"Crew resource management was not observed as none of the crew attempted to use the emergency procedures checklist to respond to the [fire]."

Cockpit video shows the flying pilot's wheel being deflected to the right and his indicating a loss of aileron control, after fire damage slackened aileron cables. He was also unsure as to whether the undercarriage was retracted.

Loss of aileron control and height led the aircraft to strike power lines in the Derdepoort industrial area and collide with a factory building. The engineer did not survive the accident and another eight occupants were seriously injured.

Investigators determined that neither pilot had been authorised to operate a South African-registered Convair 340. Although both pilots were rated on the type, neither had secured the necessary South African regulatory validation of their foreign licences.

Nor had they carried out a required competency check. They had last flown such an aircraft 17 months before the accident whereas the competency check had a 12-month limit.

The aircraft was on the verge of being transferred to an aviation museum at Lelystad in the Netherlands, and had been painted in the colours of Martin's Air Charter.

Prior to the fatal flight the aircraft had last flown on 22 February 2018, nearly five months earlier.

Rovos Rail was the registered owner of the aircraft and, on the day of the crash, had finalised and signed a sale agreement with the Dutch museum. The inquiry says the aircraft had been serviced and inspected on 6 July and that representatives of the museum were "satisfied" with both its documentation and the maintenance performed.