What happened
On 16 October 1997, an Aero Commander, AC 6T, departed Stockholm/Bromma airport for a flight to the Netherlands. Shortly after takeoff, the aircraft deviated significantly from its assigned departure route and altitude. While the pilot was navigating an incorrect heading, the aircraft entered the path of a British Airways Boeing 767 operating scheduled traffic near Stockholm/Arlanda.
The deviation brought the two aircraft into close proximity over Solna. The crew of the Boeing 767 received two separate TCAS warnings indicating a conflict with the smaller aircraft. At the closest point of approach, the aircraft were separated by approximately 2 km laterally and 690 ft vertically. Although the minimum required separation was 3 NM laterally or 1,000 ft vertically, the incident was classified as an air miss.
The investigation
The Swedish Board of Accident Investigation examined the flight paths, radar data, and crew statements. The investigation established that the Aero Commander crew failed to switch on their transponder, rendering the aircraft invisible to air traffic controllers' radar screens. This lack of visibility prevented controllers from identifying the deviation immediately.
Investigators also reviewed the cockpit environment, noting that the pilot had hired a co-pilot to assist with the flight. The investigation found that the crew had not performed a proper briefing or used standardized navigation charts to ensure agreement on the departure procedure. Instead, the pilot had provided the co-pilot with planning forms and charts without a formal review.
Findings
- The crew of the Aero Commander departed from their assigned clearance regarding both route and altitude.
- Failure to activate the transponder caused the aircraft to disappear from radar monitoring.
- The crew failed to follow established checklists, as evidenced by the forgotten frequency changes and altitude maintenance.
- Significant confusion arose because the co-pilot reversed the departure procedure and tuned the incorrect beacon, which contradicted the pilot's initial plan.
- A lack of standardized briefing and the absence of a functional two-pilot concept contributed to the breakdown in flight safety.