What happened
On August 30, 2004, at 15:53 UTC, a loss of air traffic control separation occurred approximately three nautical miles west of Helsinki-Vantaa airport. The incident involved two scheduled flights: an AVRO 146-RJ 100 (registration OH-SAN) operated by Blue1 Oy, flying from Helsinki to Oulu, and an ATR 72 (registration OH-KRH) operated by Aero Airlines As, flying from Helsinki to Mariehamina.
Both aircraft departed from runway 22R approximately 50 seconds apart. The AVRO 146-RJ 100 followed the standard ANT 1N departure route. After passing the airport noise boundary, the departure radar controller instructed the AVRO 146-RJ 100 to turn right toward the ANTON VOR. This maneuver caused its flight path to intersect the path of the following ATR 72, resulting in a minimum lateral separation of only 1.3 nautical miles.
During the climb, the crew of the AVRO 146-RJ 100 followed company procedures, which involved reducing engine thrust and retracting flaps after passing 1,500 feet. This procedure significantly reduced the aircraft's rate of climb to approximately 500 feet per minute. Consequently, the following ATR 72 began to close the vertical gap. Although the controller issued a vertical speed restriction of 1,000 feet per minute to the ATR 72, and the captain of the ATR 72 further reduced the climb rate to 200 feet per minute following a TCAS Traffic Advisory (TA), the vertical separation minimum was breached, reaching a minimum of 700 feet. Both aircraft crews received TCAS traffic advisories and established visual contact with each other.
The investigation
The investigation examined the departure procedures, the performance characteristics of both aircraft types, and the air traffic control instructions provided. The investigation established that the departure controller was managing aircraft without radar coverage and that the vertical separation between the two aircraft was not being maintained or increased as they transitioned to the departure radar controller's responsibility.
Findings
- The primary cause of the loss of separation was that the AVRO 146-RJ 100 reduced its vertical speed more than the controllers had estimated.
- The radar controller cleared the AVRO 146-RJ 100 to turn right toward ANTON, crossing the flight path of the ATR 72, even though vertical separation had already been lost.
- The radar controller failed to issue any restrictions to the aircraft other than the vertical speed limit for the ATR 72.
- The controllers lacked an accurate understanding of the differing performance characteristics and climb profiles of the two aircraft types.
- The vertical speed restriction applied to the ATR 72 was insufficient to prevent the loss of separation given the low climb rate of the lead aircraft.