Description

On 5 September 2007 in day Visual Meteorological Conditions (VMC), an MCDONNELL DOUGLAS MD-82 being operated by SAS on a scheduled passenger flight from Copenhagen to Helsinki was obliged to carry out an own-initiative avoiding action orbit in day VMC against an Airbus A319 being operated by Finnair on a scheduled passenger flight from St. Petersburg to Helsinki after conflict when about to join final approach. Both aircraft were following ATC instructions which, in the case of the MD 82, had not included maintaining own separation so that the applicable separation minima were significantly breached.

Investigation

An Investigation was carried out by the Accident Investigation Board Finland. It was found that the two aircraft had been approaching the final approach for the designated landing runway 15 from opposite directions, both initially with ATC-issued exemptions from speed control. ATC TWR had cleared the A 319 to land when it was still on a visual downwind leg. Shortly afterwards, when the A319 was still downwind but abeam the landing runway threshold, ATC APP cleared the MD82 for a visual approach but did not advise of the A319 traffic until the two aircraft were on opposite base legs at which point the MD82, having thought that the A319 was departing traffic, upon being advised that it was No 1 to land, elected to turn left, and subsequently carry out a full orbit, to create appropriate separation. The radar picture below is taken from the official report:

It was found that the minimum horizontal distance between the two aircraft was less than 1.5 nm when vertical separation was about 200 ft and that Airborne Collision Avoidance System (ACAS) advisories on both aircraft during the conflict had been limited to TA.

It was noted that Helsinki approach radar is equipped with Short Term Conflict Alert (STCA) but that it had not been in use because of the large number of ‘nuisance’ warnings created. It was also confirmed that the MD82 “had not received or acknowledged a clearance to continue visual approach maintaining own separation to the aircraft ahead” with the consequence that ATC remained responsible for providing the prescribed minimum separation for IFR traffic of 3nm / 1000ft.

There was concern that appropriate incident reporting and severity assessment did not occur:

• ATC failed to report the serious incident as required (ANSP Finavia issued new instructions during the Investigation)
• ATC deviated from the recommended severity classification scheme when determining the severity of the incident.
• The extant version of the Finnish CAA report form did not directly indicate how serious incidents should be reported. (The deficiencies found were corrected during the course of the Investigation.)

Probable Cause of the incident was determined as “the air traffic controller cleared two aircraft for visual approach for the same runway without verifying their flight paths and ensuring that the prescribed separation minima would be maintained.”

Contributing Factors were considered to be “the late traffic information provided by the controller to the aircraft, the aircraft being on different radio frequencies, and the respective approach sequence chosen for the aircraft.”

The Final Report of the Investigation was published on 3 June 2008 and subsequently translated into English. It may be seen in full at SKYbrary bookshelf: Investigation report D16/2007L

One Safety Recommendation was made as a result of the Investigation:

“That Finavia should ensure that its personnel will report any serious incidents related to air navigation services in accordance with the applicable regulations.”

Further Reading

• Loss of Separation
• Loss of Separation - ATCO-induced Situations
• ACAS Resolution and Traffic Advisories
• ATC Task Demand
• Vigilance in ATM