Investigators have determined that an Air Greenland flight was running late when its crew departed Kangerlussuaq without take-off clearance, while snow-clearance vehicles were occupying the runway.
The Bombardier Dash 8-200 had been instructed to "line up" on runway 27, via taxiway A, after requesting taxi clearance.
Three vehicles – two sweepers and a loader – had been travelling east along the runway, in the opposite direction, and were instructed to vacate.
The tower controller told the loader crew to vacate just as the Dash 8 started taxiing and, over the subsequent 60s, the two sweeper vehicles were also told to leave the runway.
Danish investigation authority HCL says that around 45s after the tower confirmed the order to vacate, the Dash 8 crew began a take-off roll, without being cleared.
The inquiry says a runway downslope meant the pilots were unable to see the three vehicles.
It states that the crew lined up and completed the 'before take-off' checklist. "The flight crew was in doubt about whether or not a take-off clearance had been issued but agreed that the aircraft was cleared for take-off," it adds.
Although a student tower controller saw the turboprop commence its take-off roll, and alerted an instructor, the instructor opted against ordering an abort after seeing the aircraft rotate.
At this point, says HCL, the aircraft was some 900m from the nearest of the snow-clearance vehicles and passed over the vehicles at around 300ft.
The inquiry says the none of the 29 occupants of the aircraft (OY-GRO) was injured in the incident on 2 March.
HCL believes the pilots were "over-motivated", because the service was 1h behind its scheduled departure time, and that they "acted from their expectations rather than the factual reality".
It adds that "soft" safety barriers – relating to phraseology and activation of landing lights after take-off clearance – did not attract sufficient attention from the crew to affect their decision-making processes.
While the inquiry has not made formal safety recommendations, Air Greenland has drawn up new procedures for pilots to acknowledge mutually air traffic control clearances.