C3/2008L Violation of separation minimums at Helsinki-Vantaa terminal control area on 29 February 2008

A significant incident occured at Helsinki-Vantaa terminal control area on 29 February 2008 at 12.45 UTC when a Finnair MD11 on a scheduled flight from Helsinki to Delhi and a Finnair A340 on a scheduled flight from Tokio to Helsinki passed each other on crossing tracks at approximately 2300 meters height so that the required separation minimums were violated. The aircraft received traffic alert (TA) from their collision avoidance systems but not collision avoidance command (RA). Both aircraft were in instrument meteorological conditions and the pilots did not get visual contact with each others´ aircraft. The Accident Investigation Board Finland on 10 March 2008 decided to appoint an investigation commission C3/2008L for this incident. Accident investigator Martti Lantela was appointed investigator-in-charge accompanied by accident investigator Vesa Kokkonen as a member of the commission.

Finnair 74 approached Helsinki from the northeast according to air traffic control clearance and was descending to flight level 80 (2450 meters). At the same time Finnair 21 departed Helsinki following according to air traffic control clearance a standard departure route, which leads southeast. The air traffic control applied vertical separation due to crossing tracks. Finnair 21 was cleared to climb to flight level 70 (2150 meters) 1000 feet below Finnair 74. Finnair 21 climbed approximately 400 feet (120 meters) above the cleared flight level.

At the time of the incident the QNH at Helsinki-Vantaa airport was 995 HPA. The pressure differential to the standard pressure, 1013 HPA, was 18 HPA. Since one HPA corresponds to 27 feet height, the total height difference was 486 feet (144 meters). Finnair 21 flew above transition altitude using QNH setting in altimeters which meant that the actual flight level was 486 feet above the indicated altitude displayed by the altimeters. Finnair 21 started to descend before it reached 7000 feet on QNH so altitude difference to Finnair 74 was approximately 600 feet. The vertical separation was violated by approximately 400 feet and horizontal radar separation by approximately 1,2 nautical miles. In this case the vertical separation should have been 1000 feet (300 meters) and the horizontal radar separation should have been 3 nautical miles (5,5 kilometers). The violation of separation minimums did not induce collision risk.

Due to the deficient cockpit crew work management, the altimeters were not adjusted to the standard pressure setting. The wrong pressure setting went unobserved and the aircraft climbed too high violating separation minimums with the other aircraft on a crossing track.

The investigation commission gave two safety recommendations:

1. In the Finnair Airbus and Embraer fleets there is an attention system that safeguards the observation of transition altitude which the other fleets of the company do not have.

The commission recommends that Finnair Oyj considers the installation of similar attention system to other aircraft fleets of the company and to the aircraft types that will be obtained in the future.

2. The present Helsinki radar system includes a conflict alert feature (Short Term Conflict Alert, STCA) but it is not in operative use due to nuisance alerts. The radar system updating is planned. One part of the updating is a new STCA feature which serves as a safety net also in parallel runway operations.

The commission recommends that with the updating Finavia obtains a STCA feature which is suitable in the Helsinki TMA airspace.

C3/2008L Report (pdf, 1.09 Mt)