A Norwegian Boeing 737-800 (LN-NON), operating flight NAX765, was about to taxi into gate 23 via taxiway K1 at Oslo-Gardermoen Airport. At the same time, flight SAS4045, a Boeing 737-800 from SAS (LN-RCY), had begun pushback on gate 13. When the tail section of SAS4045 had reached approx. 7 m outside the red line, the planes hit each other. The left wingtip on NAX765 was torn off and the rudders on the left and right sides of the SAS4045 were damaged. The hits were noticeable in both planes in the form of two bangs and light movement in the planes. There were no injuries. The danger of a collision was initiated when the flight crew in the SAS aircraft initiated a pushback without clearance being obtained from the control tower. The risk of a collision developed into an aviation accident because there was no room for simultaneous pushback and taxiing, as the infrastructure on the south side of the main terminal does not have a pushback zone, and because no other persons saw the danger of a collision. The SAS pilots were in the process of completing a training program, LIFUS (Line flying under supervision). The AIBN believes that the change of role and additional workload for the pilots in connection with the implementation of the training program had a negative effect on the pilots’ performance.