What happened
On February 29, 2008, at 12:45 UTC, a separation minimum violation occurred in the Helsinki Terminal Control Area (TMA). A Finnair MD11 (registration FIN 74) was arriving from Delhi on flight level 80, while a Finnair A3CO (registration FIN 21) was departing Helsinki for Tokyo.
To maintain separation on their intersecting flight paths, air traffic control cleared the departing A340 to climb only to flight level 70. However, the departing aircraft climbed to approximately 400 feet above its assigned altitude. At the closest point of approach, the vertical separation was only about 600 feet, and the horizontal radar separation was approximately 1.2 nautical miles. These figures fell below the required minimums of 1,000 feet of vertical separation or 3 nautical miles of horizontal separation. While the aircraft's TCAS provided a traffic advisory (TA), no collision avoidance command (RA) was issued, and the pilots did not maintain visual contact due to instrument meteorological conditions.
The investigation
The investigation examined the cockpit procedures of the departing crew and the air traffic control environment. It was established that the departing crew failed to transition their altimeters from the local QNH setting to the standard pressure setting upon passing the transition altitude. Because the local pressure (995 HPA) differed from standard pressure (1013 HPA), the aircraft's actual altitude was approximately 486 feet higher than indicated on the instruments.
Investigators also reviewed the air traffic control radar system, noting that the Short Term Conflict Alert (STCA) feature was not in operational use at the time due to frequent nuisance alerts. The investigation confirmed that the air traffic controller's actions were in accordance with existing regulations and that the separation violation did not pose an immediate risk of collision.
Findings
- The primary cause of the separation violation was deficient cockpit crew work management, which resulted in the failure to adjust altimeters to the standard pressure setting.
- The error went unnoticed until the aircraft was already climbing above its cleared altitude.
- The lack of an automated alert system for transition altitude passage in the airline's specific aircraft fleet contributed to the oversight.
- The existing STCA system at Helsinki-Vantaa was not utilized by controllers because of excessive false alarms.
Safety action
- Finnair has since updated its MD11 taxi check procedures to include a verification of the transition altitude crossing.
- The investigation recommended that Finnair consider installing altitude transition alert systems in its other aircraft fleets.
- It was recommended that Finavia implement an updated STCA system specifically optimized for the Helsinki TMA to provide a reliable safety net.