What happened
On the morning of October 31, 2012, a high-risk proximity situation occurred at Oslo Airport (Gardermoen) involving two Boeing 737-800 aircraft operated by Norwegian Air Shuttle. The incident involved flight LN-DYC (callsign NAX741) on a missed approach and flight LN-NOM (callsign NAX740) during departure.
Heavy snow and ongoing runway clearing operations had necessitated frequent runway closures, leading to a complex traffic environment. As NAX741 was on final approach to runway 01L, the crew initiated a late go-around. Simultaneously, NAX740 was cleared for takeoff on the same runway. Due to strong headwinds and a late decision to abort the landing, the aircraft entered a conflict state while both were climbing.
Because visibility was low, the tower controller could not maintain visual separation. The controller instructed NAX741 to turn west; however, due to nearly identical callsigns, the crew of the departing aircraft, NAX740, mistakenly executed the clearance intended for the arriving aircraft. This resulted in the two planes closing to a minimum horizontal distance of approximately 0.2 NM and a vertical separation of only 500 ft.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined the sequence of events, focusing on the intersection of the missed approach and the simultaneous departure. The investigation looked into the operational procedures of both the airline and the air traffic service provider, Avinor.
Investigators analyzed the impact of the weather conditions, specifically the snow removal activities that were affecting runway availability. The probe also examined the effectiveness of the communication between the tower and the flight crews, as well as the role of the Traffic Collision Avoidance System (TCAS) during the encounter. Notably, the investigation was hindered by the fact that Cockpit Voice Recorder (CVR) data from the aircraft was not secured.
Findings
- The flight crew of LN-DYC operated with unrealistic expectations regarding their ability to stabilize the approach by 1,000 ft, leading to a late decision to execute the missed approach.
- Air traffic controllers expected the landing aircraft's speed to decrease sufficiently during the approach, but this did not occur.
- Callsign confusion was a primary factor, as the crew of the departing aircraft misidentified the instruction meant for the arriving aircraft.
- The use of the phrase "when able" in the controller's instruction contributed to the crew of NAX741 believing they had more time to initiate the turn.
- There were no documented local guidelines at the Gardermoen tower for managing traffic separation specifically during simultaneous missed approaches and departures on the same runway.
Safety action
The NSIA noted that while the situation presented a real danger of collision, the situational awareness of the crews and the tower controller prevented a disaster. The authority referred to a previously issued safety recommendation regarding similar traffic management challenges at the airport.