What happened
On March 13, 1997, a military training flight was conducting a series of instrument approaches at Joensuu Airport, Finland. The aircraft, a MiG-21 UM with registration MK-105, was operating on a training route between Kuopio, Varkaus, and Joensuu.
During the approach phase, the air traffic controller provided the crew with an incorrect QFE pressure setting. The controller mistakenly read the QNH value (pressure relative to mean sea level) instead of the required QFE value (pressure relative to airport elevation). This discrepancy of 14 hPa resulted in an altitude error of approximately 112 meters.
As the aircraft performed an ILS approach, the crew descended below the minimum descent altitude. The aircraft reached a minimum height of approximately 60 meters above the ground, significantly below the target minimum of 129 meters. The instructor pilot, monitoring the flight from the rear cockpit, received a terrain warning from the radio altimeter and ordered an immediate go-around. Following the climb, the crew queried the pressure setting, at which point the controller realized the error and provided the correct QFE of 9t3 hPa.
The investigation
The investigation examined the air traffic control procedures at Joensuu, the communication between the controller and the crew, and the cockpit environment. Investigators reviewed the controller's workload, noting it was his sixth consecutive shift, though his alertness was deemed good. The investigation also looked at the lack of an ATIS (Automatic Terminal Information Service) at the airport, which would have broadcasted the correct weather and pressure settings automatically.
Findings
- The primary cause of the incident was that the air traffic controller provided an incorrect altimeter setting to the aircraft.
- The controller mistakenly communicated the QNH value instead of the QFE value.
- The aircraft's crew did not correct the controller's incorrect instruction regarding the approach type (ILS vs NDB) or the failure to report passing the beacon inbound.
- The instructor pilot's use of the radio altimeter and terrain warning system was critical in identifying the low altitude and initiating the go-around.
- The absence of an ATIS system at Joensuu meant pilots had to rely entirely on verbal instructions for pressure settings.
Safety action
- The investigation board recommended that Joensuu and similar aerodromes consider the implementation of an ATIS system to reduce the risk of manual communication errors regarding weather and pressure settings.