B733, vicinity Helsinki Finland, 2008

Summary: 

On 26 March 2008, a Ukraine International Airlines Boeing 737-300 being vectored by ATC to the ILS at destination Helsinki in IMC descended below its cleared altitude and came close to a telecommunications mast. ATC noticed the deviation and instructed a climb. The investigation attributed the non-compliance with the accepted descent clearance to the failure of the flight crew to operate in accordance with SOPs. It was also noted that the way in which ATC safety systems were installed and configured at the time of the occurrence had precluded earlier ATC awareness of the hazard caused by the altitude deviation.

Event Details
When: 
26/03/2008
Event Type: 
Day/Night: 
Day
Flight Conditions: 
IMC

18946

Flight Details
Aircraft: 
Type of Flight: 
Public Transport (Passenger)
Intended Destination: 
Take-off Commenced: 
Yes
Flight Airborne: 
Yes
Flight Completed: 
Yes
Phase of Flight: 
Descent
Location
Location - Airport
Airport: 
General
Tag(s): 
Altimeter Setting Error, Event reporting non compliant, Inadequate Aircraft Operator Procedures, Inadequate ATC Procedures
CFIT
Tag(s): 
Into terrain, Vertical navigation error, IFR flight plan
HF
Tag(s): 
Data use error, Distraction, Ineffective Monitoring, Procedural non compliance, Ineffective Monitoring - SIC as PF
LB
Tag(s): 
Accepted ATC Clearance not followed, Manual flight
Outcome
Damage or injury: 
Yes
Non-aircraft damage: 
Yes
Non-occupant Casualties: 
No
Off Airport Landing: 
Yes
Ditching: 
Yes
Causal Factor Group(s)
Group(s): 
Aircraft Operation
Safety Recommendation(s)
Group(s): 
Aircraft Operation, Air Traffic Management
Investigation Type
Type: 
Independent

Description

On 26 March 2008, a Ukraine International Airlines’ Boeing 737-300 operating a scheduled passenger flight from Kiev to Helsinki descended below its ATC cleared altitude and MSA in day IMC whilst being vectored to the ILS and camer close to a telecommunications mast before ATC noticed the error and ordered it to immediately return to the cleared altiude. There were no abupt manoeuvres and none of the 29 occupants were injured.

Investigation

An Investigation was carried out by the Accident Investigation Board Finland (AIBF). FDR and CVR data was not available but QAR data was and this proved invaluable to the Investigation. This data showed that the aircraft had descended to an altitude of 1400-1500 feet in the vicinity of the 1227 feet high mast before ATC instructed a climb. It was noted that the First Officer had been PF.

It was concluded 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 SOPs (SOP). The detection of the incident was delayed by the facts that the Terrain Awareness and Warning System (EGPWS) did not warn of the telecommunications mast and that the MSAW (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."

In respect of Probable Cause, the Investigation found that: "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 and the fact that the pilots deviated from Standard Operating Procedures."

The following Safety Recommendations were made as a result of the Investigation:

  • that the airline 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.
  • that Finavia incorporate a Minimum Safe Altitude Warning (MSAW) feature for the Helsinki Terminal Control Area in its next radar software update. "

Related Articles

Altimeter Setting Procedures

Further Reading

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