C4/2008L Terrain clearance infringement in Helsinki Terminal Control Area on 26 March 2008

A serious incident occurred in the Helsinki Terminal Control Area on 26.3.2008 at 14:39 UTC. A Ukraine International Airlines’ Boeing 737 airliner descended below its ATC clearance altitude. Accident Investigation Board Finland (AIB) appointed investigation commission C4/2008L for this incident. Investigator Markus Bergman was named Investigator-in-Charge with Investigator Juha Salo as a member of the commission. On 24.4.2008 Investigator Erkki Kantola was named as an additional member to the commission. Speech and Audio Expert Dr. Päivikki Eskelinen-Rönkä assisted the investigators in analysing the recorded radiotelephony.

While being radar vectored to the Helsinki-Vantaa aerodrome the airliner was cleared to 2300 FT. However, it descended to 1400 FT, at its minimum, breaking the minimum terrain clearance with a telecommunications mast ahead of its track. The air traffic controller noticed that the airliner had deviated from its clearance altitude and ordered it to immediately return to 2300 FT.

Investigation revealed that the incident was caused by an incorrect altimeter pressure setting indicating an altitude which was more than 1000 FT erroneous. The wrong altimeter setting was the result of the pilots deviating from their Standard Operating Procedures (SOP). The investigation could not establish an unequivocal reason for the action of the flight crew. The detection of the incident was delayed by the facts that the Enhanced Ground Proximity Warning System (EGPWS) did not warn of the telecommunications mast and that the Minimum Safe Altitude Warning (MSAW) feature in use at Helsinki Air Traffic Control is not utilised for alerting infringements of the minimum safe altitude. Furthermore, investigation revealed that, in violation of airline regulations, the pilots did not report the incident to the aviation authorities or to the airline. The air traffic controller did report the occurrence, albeit simply as an incident. However, by definition, it was a serious incident.

The serious incident was caused when the aircraft descended below its ATC clearance altitude, creating the risk of collision with a telecommunications mast ahead of its track. The cause of breaking the clearance altitude was an erroneous altimeter setting. Contributing factors included inadequacies in Crew Resource Management (CRM) and the fact that the pilots deviated from Standard Operating Procedures (SOP).

The investigation commission issued two recommendations. First: The airline is to ensure that their pilots possess the required information and skills for proper Crew Resource Management, as required by the safe conduct of aviation and compliance with airline operations manuals. Second: Finavia is to incorporate a Minimum Safe Altitude Warning (MSAW) feature for the Helsinki Terminal Control Area in its next radar software update.

C4/2008L Report (pdf, 1.05 Mt)