What happened
On 10 June 2008, at approximately 10:54 local time, two aircraft operated by the Finnish Aviation Academy were involved in a serious air proximity incident near Pori aerodrome. The aircraft involved were a BE30 King Air, registration OH-BSB, performing an instrument training flight, and a BE3/36 Bonanza, registration OH-BBN, conducting an instrument rating check flight. Both aircraft were operating under simulated instrument flight conditions.
The air traffic controller (ATC) initially cleared OH-BBN to the FR waypoint at 2700 feet for an ILS approach, but subsequently issued a new clearance to the PITUM waypoint at 1700 feet. Simultaneously, OH-BSB, which had departed from runway 12, was cleared to 1700 feet and later to the PITUM waypoint at the same altitude.
As both aircraft reached 1700 feet, their flight paths intersected at a 90-degree angle over the PITUM waypoint. At 10:54, OH-BBN crossed the flight path of OH-BSB approximately 2.3 NM ahead of it. Shortly after passing PITUM, OH-BBN turned to a heading of 120 degrees, placing the two aircraft on a head-on collision course. Approximately 30 seconds later, the TCAS on OH-BSB issued a Traffic Advisory (TA) followed immediately by a Resolution Advisory (RA). The pilot of OH-BSB executed an immediate descent to avoid the conflict. While the pilot of OH-BSB reported seeing the other aircraft at a distance of about 0.5 NM, the crew of OH-BBN reported that they did not see the other aircraft at any point.
The investigation
The investigation examined the air traffic controller's communications, the flight progress strips, and the operational procedures of both crews. The investigation established that while the controller had correctly noted the 2700-foot altitude on the flight progress strip for OH-BBN, they had inadvertently broadcast a clearance of 1700 feet over the radio.
Investigators also looked into the status of the FR locator, which had been reported unserviceable via NOTAM. Although the locator was actually functioning and transmitting, there was no clear indication on the controller's desk that it was out of service, leading the controller to use it as a clearance limit out of habit.
Findings
- The primary cause of the incident was the air traffic controller inadvertently issuing an erroneous altitude clearance via radio, despite having recorded the correct altitude on the flight progress strip.
- The flight crews did not sufficiently monitor radio communications, and neither the active nor the relief air traffic controller noticed the error in the altitude clearance.
- The crews failed to provide all necessary and timely position and altitude reports required for procedural control.
- The FR locator was unserviceable according to NOTAM, but the lack of a clear notation on the controller's strip board led the controller to use it as a clearance limit by habit.
- The crews' focus on instructional tasks and the high workload of instrument training may have contributed to the lack of situational awareness regarding the conflicting clearances.