C5/2004L Loss of air traffic control separation west of Helsinki-Vantaa airport on 30 August 2004

On Monday 30 August 2004 at 15.53 UTC (Finnish local time -3h), a loss of air traffic control separation occurred about three nautical miles west of Helsinki-Vantaa airport between an AVRO 146-RJ 100 airliner, operated by Blue 1 Ltd. on a scheduled flight from Helsinki to Oulu (call sign BLF209), and an ATR 72 airliner operated by Aero Airlines As on a scheduled flight from Helsinki to Maarianhamina (call sign EAY209). Both vertical and horizontal separation minima were infringed after departure.

On 16 September 2004 the Accident Investigation Board (AIB), Finland, decided to investigate the incident. Air traffic controller Mr Erkki Kantola was appointed as investigator-in-charge, and airline transport pilot Mr Jussi Haila as a member of the investigation commission.

BLF209 departed for Oulu from Helsinki-Vantaa runway 22R at 15.50, following the standard instrument departure ANT 1N. EAY209 took off from the same runway about 50 seconds later. After departure the aircraft flew radar heading 280°, having been cleared to the altitude of 4000 ft. When BLF209 had passed the airport noise boundary, which is 2.5 nautical miles of the end of Helsinki-Vantaa runway 22R and had been marked on the video map on ATC radar display, the departure radar controller (DEP) instructed BLF209 to fly to the right towards ANTON. After the turn the flight path of BLF209 intersected EAY209’s flight path from left to right. The shortest horizontal distance between the aircraft was 1.3 nautical miles.

BLF209 had been cleared to climb to flight level 230. During the climb, the crew followed the company’s current operation procedure, according to which the reduction of engine thrust from take-off to climb setting, flap retraction and acceleration should be made after passing through 1500 ft. For this reason the vertical speed of BLF209 was considerably slow, and EAY209 flying behind it started to reach it in altitude. The air traffic controller noticed this and issued EAY209 a vertical speed restriction of 1000 feet per minute. At the same time, the TCAS equipment of EAY209 gave a traffic advisory (TA), and the captain reduced the climb rate further into 200 ft/min, almost levelling off. However, this did not prevent the loss of vertical separation. The shortest vertical distance between the aircraft was 700 feet. The TCAS systems of both aircraft issued a TCAS traffic advisory, and the pilots of both aircraft also got the other aircraft in sight. All parties involved made an incident report in writing.

The air traffic control separation was lost, since BLF209 slowed down its vertical speed more than the controllers had estimated. Contributing factors were: 1. The radar controller cleared BLF209 to turn right towards ANTON across the flight path of EAY209, although the required vertical separation between the aircraft had already been lost; 2. The radar controller issued no other restrictions to either aircraft than the vertical speed restriction for EAY209.

C5/2004L Report (pdf, 0.56 Mt)