C4/2003L Loss of separation minima in the Helsinki Terminal Control Area on 27 April 2003

On Sunday, April 27, 2003, at 17.33 hrs Finnish time a loss of separation minima occurred in the Helsinki Terminal Control Area. The Accident Investigation Board Finland decided to appoint an investigation commission on May 6, 2003, to investigate the incident. Timo Uramaa, investigator, was appointed chairman of the commission and Erkki Rissanen, investigator, appointed member of the commission.

A passenger aircraft Boeing 757-200 homebound from Rhodos, call sign FIN 2710, operated by Finnair Oyj, was approaching runway 22L at Helsinki-Vantaa airport under radar vectoring. There were 217 persons in total on board of which 9 belonged to the crew. At the same time a passenger aircraft Saab 340 A, call sign GAO 338, operated and owned by Golden Air Flyg AB, was taking off from runway 15 to Savonlinna with an initial clearance of Porvoo 4R standard instrument departure route. There were 17 persons in total on board of which 3 belonged to the crew. Its initial clearance altitude was 3000 ft above mean sea level. During the first radio contact the approach control (DEP) still confirmed the clearance of maintaining 3000 ft. From the approach control (APP) FIN 2710 got a clearance to descend to the altitude of 4000 ft. The go-pilot misheard their clearance altitude and read back 3000 ft. APP did not notice the error but confirmed the read-back. FIN 2710 continued its descent towards the altitude of 3000 ft

The flight paths of the two aircraft crossed at an intersection point 6.3 NM from the runway intersection at the Helsinki airport with bearing 102 degrees. Both DEP and APP noticed on their radar altitude display how FIN 2710 continued its descent through the altitude of 4000 ft. APP requested confirmation of altitude from the aircraft, which reported to be at the altitude of 3600 at that moment. APP ordered the aircraft to climb to 4000 ft. FIN 2710 was delayed in starting its climb because the crew forgot the air brakes out for 18 seconds. If they had immediately taken the air brakes in and the climb had been started instantly, it is probable that no loss of separation would have taken place. When APP noticed that the minimum horizontal separation between the two aircraft would be lost, it ordered FIN 2710 to turn to left to heading 270. The loss of required horizontal/vertical separation between the aircraft lasted for 40 seconds. Their shortest horizontal distance from each other was 1.2 NM and the shortest vertical distance was 157 ft. The required horizontal separation is 3 NM provided that the vertical separation is at least 1000 ft (300 m). The TCAS system (Traffic alert and Collision Avoidance System) of FIN 2710 had generated a “Climb” RA advisory of intruder aircraft. The pilots got also visual contact with the intruder, which they reported to the air traffic control.

The incident occurred when the FIN 2710 first officer misheard their clearance altitude and the air traffic controller did not notice the mistake in the read-back. The air traffic controller’s order to climb back to 4000 ft would probably have prevented the loss of separation if the FIN 2710 crew had not forgotten the air brakes out for 18 seconds.

The investigation commission does not give any safety recommendations.

C4/2003L Report (pdf, 0.64 Mt)