Reduced Separation Incident Involving British Airways Citiexpress and Scandinavian Airlines System in Oslo TMA (G-EMBX, LN-RMN)

Incident Overview and Aircraft Details On September 4, 2002, at 1011 local time, an air traffic incident involving reduced separation and a TCAS/RA occurred in the Oslo TMA, north of ENGM. The incident involved two aircraft: an Embraer ERJ 145 with registration GE-MBX, operating as British Airways Citiexpress flight BRT866, and an MD-87 with registration LN-RMN, operating as Scandinavian Airlines System flight SAS454. Both flights were engaged in scheduled commercial operations. The weather conditions were visual, daylight, and VMC, with both flights operating under IFR flight plans. The number of persons on board was unknown, and there were no injuries or damage reported to the aircraft or other property. ## Sequence of Events At the time of the incident, traffic at Oslo Airport Gardermoen (ENGM) was considered moderate and was controlled by TMA E. BRT866 was being radar vectored for the ILS RWY 19 L. Simultaneously, SAS454 was descending to 5,000 ft on the left downwind leg for RWY 19L, in accordance with its clearance. SAS454 then received a new instruction from TMA E to descend to 4,000 ft. The air traffic controller observed that SAS454 had initiated a left turn towards the base leg for RWY 19L, which was not in accordance with the clearance. TMA E requested SAS454's intentions, and the crew responded, “We have traffic in sight.” ## Controller Response and Separation In response, the air traffic controller at TMA E immediately instructed SAS454 to stop descending at 4,000 ft and to turn right to a heading of 360 degrees. SAS454 complied with these instructions. The separation between the two aircraft at the closest point of approach was 2 NM and 600 ft. BRT866 received a TCAS/RA during its final approach. The incident was reported to TWR in accordance with regulations. ## Investigation and Contributing Factors The Norwegian Aircraft Accident Investigation Board (AAIB-N) compiled this report using a simplified format due to the limited extent of the investigation. The investigation relied on the report from Oslo ATCC and the AAIB-N's own investigations. The AAIB-N noted that, since the traffic was controlled by TMA E, SAS454's unmotivated base turn towards RWY 19L was considered the major contributing factor to the incident. The report was issued for the sole purpose of improving flight safety, with no intention to apportion blame or liability.