What happened
On the afternoon of September 12, 2002, a Jetstream 3200-3201, operating as flight HS476, was prepared for departure from Norrköping/Kungsängen airport to Visby. During the taxi phase, the air traffic controller issued a clearance to fly via the ON NDB, maintaining 3,000 feet. The flight crew acknowledged and copied this instruction.
As the aircraft took off from runway 09, it was climbing through the area where a Beech B95A, registration SE-EKW, was established in a holding pattern at 4,000 feet. Shortly after takeoff, the crew of the Jetstream reported to Östgöta Control that they were climbing to Flight Level 90. The air traffic controller, observing the rapid ascent on radar, attempted to interrupt the crew's transmission to issue an immediate descent instruction. The Jetstream had already passed 3,300 feet and continued to climb to 3,500 feet before the descent was corrected. The closest proximity between the two aircraft was approximately 500 meters horizontally and 180 meters vertically.
The investigation
The Swedish Accident Investigation Board examined the flight procedures, cockpit communications, and air traffic control management. The investigation looked into the crew's use of the Altitude Preselect Alert (APA) and the specific instructions provided by the tower. The inquiry also reviewed the air traffic controller's management of the holding pattern and the timing of clearances issued during the taxi-out phase.
Findings
- The crew of SE-LHB failed to maintain the assigned altitude, climbing through the cleared 3,000-foot limit.
- The aircraft's Altitude Preselect Alert (APA) was set to 9,000 feet and was not updated to the cleared altitude of 3,000 feet.
- The pilots of the Jetstream 3200-3201 forgot the specific altitude restriction contained in their clearance.
- The air traffic controller had placed the Beech B95A in a holding pattern at a beacon that was also being used as a departure fix for the departing aircraft.
- An unofficial practice existed within the operator's organization where departing crews performed equipment pre-settings before the taxi-out process began.