B8+8a/1997L ATC Incidents near Vihti VOR Radio Beacon, Finland, on 25 October 1997 and on 20 August 1997

On Saturday 25 October 1997 at 12.23 local time east of Vihti VOR there was an air incident which endangered flight safety. The incident concerned two aircraft owned and used by Finnair. The aircraft were a DC-9-82 registered OH-LMW and a DC-9-51 registered OH-LYS. The first one was flying the scheduled flight AY836 from London to Helsinki and the second one the scheduled flight AY365 from Helsinki to Oulu. The incident took place at an altitude of about 10.000 ft when the aircraft passed each other on intersecting flight paths below separation minimums. According to the flight data recorders the vertical distance between the aircraft was about 300 ft at the moment of intersection. There were 152 people on board in all.

The Accident lnvestigation Board (AIB), Finland appointed on 28 October 1997 by letter No. B 8/1997 L an investigation commission to investigate the incident in accordance with the Finnish legisiation on investigation of accidents. Colonel (ret.) Mr Jouko Koskimies was appointed investigator-in-charge. Airline pilot (ret.) Mr Jussi Haila, air traffic controller Mr Ari Huhtala and psychologist, Ph.D. Ms Leena Norros were appointed members of the commission. The investigation commission began the investigations on 28 October 1997. All parties concerned with the incident were heard between 17 November 1997 and 10 December 1997 in Helsinki and Vantaa. The first briefing for media representatives was arranged on 13 November 1997 at the Accident Investigation Board.

On Wednesday 20 August 1997 at 19.20 local time south of Vihti VOR there was an air incident which endangered flight safety. The incident concerned two aircraft owned and used by Finnair. The aircraft were a DC-9-51 registered OH-LYO and a DC-9-51 registered OH-LYZ. The first one was flying a scheduled flight AY646 from Stockholm to Helsinki and the second one was on a training flight AY9803 from Helsinki to Turku. The aircraft would have passed each other below separation minimums, if the air traffic controller in charge had not ordered the corrective clearances, actually fairly late. However, the AY9803 took an avoiding manoeuvre. There were 8 people on board in all.

The Accident Investigation Board considered that the incident was similar to the incident on 25 October 1997 and appointed on 13 November 1997 by letter no. B 8a/1997 L the abovementioned commission to investigate the incident. The investigations had been started by the Flight Safety Authority (FSA) of the Finnish Civil Aviation Administration (FCAA) and were continued by the Accident lnvestigation Board. The investigation began on 13 November 1997. All parties concerned with the incident were heard between 17 November 1997 and 10 December 1997.

The investigation is done according the case-based method and the chain of events leading to the incident is explained separately for both cases. Factual information, analysis and causes of the incidents are contained in parts 1 and 2.

On the basis of the investigations the operation of Helsinki-Vantaa APP was studied and the results are shown in part 3. Research methods developed by VTT Automation were used in this study.

The safety recommendations of the commission are given in part 4.

The final draft of the investigation report was sent according the legisiation to the FCAA for comments on 9 June 1998. Comments were received on 9 July 1998 and they have been taken into account in the report.

B8+8a/1997L Report (pdf, 0.75 Mt)