Investigators were forced to base their conclusions on interviews with the pilots in the absence of flight data and voice recordings from the cockpit.
“It’s unfortunate that the data vanished along the way,” the head of the inquiry Stefan Christensen told newspaper Södermanlands Nyheter.
“This time it went okay without the recordings but on another occasion that might not be the case.”
The Ryanair plane - a Boeing 737 bound for Paris with 179 passengers onboard in late April 2011 - was forced to make an emergency landing at Skavsta following en electrical failure. The accident inquiry concluded that it had been a serious safety incident.
Robin Kiely, head of communications at Ryanair told Södermanlands Nyheter that there was nothing unusual about the fact that the black box data was erased.
“The sound recording was restarted by a technician who was repairing the electrical fault. The decision was taken by our technical department – they did not see any need to keep the recording,” he said.