B2/2008L Air proximity incident close to Pori aerodrome 10 June 2008

On 10 June 2008 two aircraft belonging to the Finnish Aviation Academy were involved in an air proximity incident close to Pori aerodrome. OH-BBN (BE36 Bonanza) was on an instrument rating check flight, as per the syllabus of the Academy. OH-BSB (BE30 King Air) was on an instrument training flight. At 10:54, during their approach phases in simulated IMC conditions, both aircraft maintained 1700 ft (approximately 500 m) above the initial approach fix (IAF) PITUM and flew towards each other. OH-BSB executed a TCAS manoeuvre. The incident did not result in any damage. Accident Investigation Board Finland (AIB) appointed investigation commission B2/2008L for this incident. Investigator Jouko Koskimies was named Investigator-in-Charge with Investigator Martti Lantela as member of the commission.

Air traffic control cleared OH-BBN from Pori instrument training area B to initial approach fix FR at 2700 ft for an ILS Y approach to runway 30. A moment later the air traffic controller recleared it to initial approach fix PITUM at 1700 ft for an ILS Z approach to runway 30.

Air traffic control cleared OH-BSB, departing runway 12, to FR at 1700 ft. A moment later the ATC recleared OH-BSB to PITUM at 1700 ft.

Some forty seconds after takeoff OH-BSB reached the clearance altitude 1700 ft. After it passed PITUM the air traffic controller cleared it for an ILS Z approach to runway 30. OH-BBN flew towards PITUM, heading around 200 degrees, and reached 1700 ft just before arriving at PITUM. Both aircraft were now flying at the same altitude. When OH-BSB reached the final approach track, the flight paths of the aircraft crossed at an approximate 90 degree angle. At 10:54 OH-BBN crossed the flight path of OH-BSB approximately 2.3 NM ahead of it. After passing PITUM OH-BBN turned towards the heading of 120 degrees, causing the aircraft to now be heading towards each other.

Some thirty seconds later the TCAS system on OH-BSB generated a Traffic Advisory (TA), directly followed by a Resolution Advisory (RA). OH-BSB immediately initiated a TCAS descent. The pilot in command of OH-BSB reported having seen an approaching aircraft approximately half a mile away. The pilot reported the TCAS manoeuvre to air traffic control, notified that they were clear of conflict and climbed back to 1700 ft. According to their statement neither pilot on OH-BBN spotted the other aircraft at any phase of the incident.

Immediately after the incident the air traffic controller realized that he had inadvertently cleared OH-BBN to 1700 ft on the radio, even though he had marked 2700 ft as the clearance altitude on the flight progress strip. Both aircraft followed their clearances and none of the pilots noticed that they had been cleared to the same fix at the same altitude. The erroneous altitude clearance went unnoticed by the air traffic controller in charge as well as by the other air traffic controller who was working the same shift.

Both aircraft continued their flights as planned after the incident. The pilots in command of both aircraft as well as the air traffic controller reported the incident as required.

The cause of the incident was the air traffic controller inadvertently issuing an erroneous clearance altitude on the radio, even though he had marked it correctly on the flight progress strip.

Contributing factors include:

• The aircrews did not adequately monitor radio communication neither did anybody notice the mistake
• The locator FR was informed by notam to be unserviceable, but this was not clearly indicated on the flight progress strip board and the air traffic controller, out of habit, used it as a clearance limit. The locator was, however, operating and transmitting its identification code and a bearing indication.
• The aircrews did not correctly report all positions and altitudes essential in Procedure Control.

The investigation commission made no safety recommendations.

B2/2008L Report (pdf, 1.04 Mt)