What happened
On July 15, 1996, at approximately 17:03, a near mid-air collision occurred in the Helsinki approach area near Malmi Airport. A McDonnell Douglas DC-9-82, operating as AY 882, was being vectored for a visual approach to runway 22 at Helsinki-Vantaa. Simultaneously, a Cessna 1 50, registration OH-CDA, was performing aerobatic maneuvers in a reserved airspace block between 2,000 and 4,000 feet above the Malmi area.
During the approach, the approach controller coordinated a heading change for AY 882 to a heading of 040 degrees to expedite the arrival. While the coordinator approved this change, the incoming approach controller—who had recently taken over the shift—misinterpreted the altitude information on the flight strip. The captain of AY 882 noticed the Cessna 150 at a similar altitude ahead and immediately notified the controller. The pilot of OH-CDA also observed the large airliner approaching closely and ceased aerobatic maneuvers to maintain separation. The aircraft passed each other safely.
The investigation
The investigation examined the coordination between the radar coordinator and the approach controller, the clarity of flight strip markings, and the controller's duty status. Investigators found that the approach controller had not received the minimum required rest period between shifts, although his alertness was reported as normal. The investigation also looked into why the reserved airspace was not visible on the radar display, noting that certain warning markers were not active for that specific area at the time.
Findings
- The approach controller misinterpreted the altitude marking on the flight strip, reading a '3' as a '5', which led him to believe the aircraft was at 5,000 feet, safely above the aerobatic zone.
- The approach controller directed AY 882 into the restricted airspace.
- The radar coordinator approved the heading change without noticing that the new path would enter the reserved aerobatic area.
- The reserved airspace was marked on the controllers' flight strips but was not displayed on the radar screen due to the use of different warning markers for other areas.
- The pilot of AY 882 and the pilot of OH-CDA both took proactive measures to avoid a collision.
- The approach controller had not completed the minimum rest period between work shifts.