What happened
On March 15, 1997, at approximately 12:30 local time, a serious air traffic safety incident occurred near Rovaniemi Airport. A Royal Air Force C-130 Hercules, operating as MET59 for meteorological research, was descending through the Rovaniemi area. Simultaneously, a Cessna 182, registration OH-CTS, was conducting a parachuting operation, dropping five jumpers at an altitude of approximately 1,500 meters.
As the Hercules aircraft crossed over the airport, it passed extremely close to the parachutists. The pilot of OH-CTS observed a large grey aircraft passing just below the cockpit during the exit of the second jumper. Two of the three jumpers experienced the aircraft's wake turbulence as they fell through its flight path. The first jumper passed approximately 20 meters in front of the Hercules, while the subsequent jumpers passed behind it.
The investigation
The investigation examined the radio communications between the aircraft and Rovaniemi approach control, as well as the flight plans and altitude assignments. The investigation established that the air traffic controller was performing duties in the approach position with very low routine, having not worked that specific post for over four months.
Investigators also reviewed the altitude information provided by the aircraft. While the controller had asked for the maximum jump altitude, the information provided by the pilot of OH-CTS was given in QFE (pressure relative to the airfield), whereas the Hercules was operating based on altitude relative to mean sea level (QNH). This discrepancy led to a misunderstanding of the actual vertical separation between the two aircraft.
Findings
- The primary cause of the incident was that the air traffic controller failed to ensure vertical separation between the overflying Hercules and the parachuting aircraft.
- The controller relied on a visual impression from the flight plan, assuming the Hercules would fly above all other traffic, and did not calculate the actual altitude difference between the two aircraft.
- A significant contributing factor was the use of different pressure references; the controller interpreted the jump plane's altitude as 4,000 feet QNH, but the aircraft was actually climbing to 1,500 meters QFE, placing the aircraft at nearly the same altitude as the Hercules.
- The controller's lack of recent experience in the approach control position contributed to the oversight.
- The pilots of the jump aircraft and the jumpers did not immediately report the incident to the authorities, as they did not initially perceive a direct collision risk.