C4/2010L Air proximity incident in Pori Terminal Area on 10 June 2010

A serious incident occurred southeast of Pori aerodrome on Thursday, 10 June 2010 at 13:09 when two Beechcraft BE36 Bonanza aircraft (OH-BBN and OH-BBM) were involved in an air proximity (Airprox) incident. OH-BBN was on a modular flight training course skill test for instrument rating IR (A) as per the training manual of the Finnish Aviation Academy. OH-BBM was on a Finnish Aviation Academy training flight. Air traffic control had cleared OH-BBN for an instrument approach to runway 30 from the altitude of 1700 ft QNH (518 m). OH-BBM, approaching from the direction of Turku, was cleared to maintain FL 70 or above until passing a certain fix after which it could descend to 2700 ft (823). The pilot of the aircraft that received this clearance incorrectly read back the clearance; acknowledging 1700 ft as the clearance altitude. The pilot then descended to the incorrect altitude. Both aircraft simultaneously passed the Initial Approach Fix for runway 30 at almost identical altitudes. According to radar recordings the minimum lateral distance between the aircraft was approximately 0.1 NM (180 m) and the minimum vertical distance was 100 ft (30 m). Neither aircrew spotted the other aircraft. The incident did not result in any damage. Both pilots-in-command and the air traffic controller filed the appropriate reports regarding the incident.

The serious incident developed when the pilot of the aircraft that was on the training flight followed the incorrectly acknowledged clearance. Neither the flight instructor nor the air traffic controller noticed the error; the air traffic controller inadvertently acknowledged it as being correct. The air traffic controller was working alone and traffic was heavy. This contributed to the occurrence and may have impaired the controller’s ability to pay close attention to the read-back. Furthermore, visitors inside the control tower were disturbing the air traffic controller’s concentration to a degree.

Clearance read-back is an essential part of aviation safety culture. The investigation commission recommends that Finavia Corporation and the Finnish Aviation Academy pay particular attention to correct clearance read-back as well as to listening to clearance acknowledgements in air traffic controller and pilot training.

When it comes to Pori aerodrome’s instrument approach charts, the fixes for different approach methods are only required to be reported upon at the request of the air traffic controller. Nonetheless, the aerodrome’s approach control is based on procedural control, which always requires up-to-date positional and altitude information. Considering the present volume of air traffic it is also important to minimise radio traffic. The investigation commission recommends that Finavia Corporation either make the instrument approach charts analogous with air traffic control procedures, or introduce radar information in control towers at procedural control aerodromes corresponding to Pori.

The computer displays in Pori tower notably impair visibility to the movement area. The investigation commission recommends that Finavia Corporation ergonomically modernise the Pori tower workspace, making it easier for air traffic controllers to visually monitor the movement area.

Pori aerodrome’s VHF Direction Finding Station (VDF) has been out of service since the spring of 2008. The investigation commission recommends that Finavia Corporation return the device to service as soon as possible. Even though a VDF is not ATS-required equipment, it still improves flight safety and alleviates the air traffic controller’s workload.

C4/2010L Report (pdf, 1.08 Mt)