What aircraft was involved and where did it happen?

The accident on 1997-05-20 involved a aircraft, registration OH-KRC, at FI.

Near Mid-Air Collision Avoided Near Tampere

A separation loss between an ATR 72 and a Cessna 500 occurred near the Pirkan VOR due to an unauthorized climb through assigned altitude.

What happened

On May 20, 1997, at approximately 12:30 UTC, a near mid-air collision occurred in the western sector of Tampere Approach. The aircraft involved were a Finnair ATR 72, registration OH-KRC (operating as Fin 3ự35), and a Cessna 500, registration OH-COC.

Fin 335 was en route from Kruunupyy to Helsinki, climbing from flight level 92 to 190. Simultaneously, the Cessna 500 was departing from Kauhavo with an intended cruise altitude of 250. To maintain separation, the air traffic controller initially restricted the Cessna 500 to a flight level of 90. As the ATR 72 climbed through 180, the controller cleared the Cessna 500 to climb to 170, and later to 180, once the ATR 72 had reached 190.

While the aircraft were flying nearly parallel with similar groundspeeds, the controller observed the Cessna 500 climbing through its assigned level of 180. Radar data indicated the Cessna 500 reached a peak altitude of 186 before descending back to 180. The crew of the ATR 72 reported seeing the light business jet approximately 200 meters to their right and about 300 to 600 feet below them. The crew of the Cessna 500 did not visually identify the ATR 72 at any point during the encounter.

The investigation

The investigation examined radar data, radio communications, and pilot reports. The controller was utilizing secondary surveillance radar height information for separation. The investigation focused on why the Cessuna 500 exceeded its assigned altitude and why the crew failed to maintain visual separation or notice the altitude deviation.

Findings

The primary cause of the near mid-air collision was the Cessna 500 climbing above its assigned altitude.
Several contributing factors were identified, including the possibility that an incorrect altitude was programmed into the aircraft's altitude warning system.
Inadequate communication between the captain and the first officer of the Cessna 500 may have contributed to the deviation.
A potential flight control error may have occurred while the crew was attempting to level off at the assigned altitude.
The crew of the Cessna 500 failed to observe the ATR 72 during the encounter, likely due to the small horizontal distance between the aircraft and limited upward visibility from the cockpit.