Investigation Summary
The flight was operating the second leg of a Helsinki to Mariehamn route with a stopover in Turku. The aircraft departed Turku carrying 21 passengers, three crew members, one deadheading passenger, 789 kilograms of cargo, and 1,100 litres of fuel. Despite weather conditions at Mariehamn being near or below operational minima due to dense fog, the crew elected to proceed. The approach was conducted at 2,000 feet using two non-directional beacons (NDB), as the airport lacked an instrument landing system (ILS) or radar. During the final approach, the aircraft remained perfectly aligned with the runway centerline but descended below the safe obstacle clearance altitude. The investigation highlighted that the captain's altimeter had a known defect, having shown a 50-foot error the day before. It was theorized that the pilot might have attempted to compensate for this error in the wrong direction or that a new malfunction occurred during the descent. Additionally, the presence of an unauthorized deadheading passenger, a former fighter ace, in the cockpit was noted, though investigators concluded this did not contribute to the accident. The crash remains the second deadliest in Finnish aviation history.
Final Conclusions
The Accident Investigation Board (AIB) concluded that the ultimate cause was the pilot's misconception of altitude. This was attributed to either a wrong indication from a defective altimeter or human error in correcting for a known altimeter discrepancy. The aircraft descended below the safe flying altitude during an instrument approach in weather conditions worse than approved minima, leading to the collision with trees.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Pekka Marttinen
First Officer
Pekka Yli-Niemi
Systems & Failure Modes
Altimeter
The pilot-in-command's altimeter was found to have a defect that could cause wrong indications, which the pilot could not have foreseen.
NDB (Non-Directional Beacon)
The airport relied on 'MAR' and 'Locator S' beacons for navigation; investigators examined if the 'Locator S' beacon provided false radio compass readings.
Approach Lighting
A low-power lighting system existed but did not extend to the area of the highest obstacles near the beacon.
Interesting Facts
- 01The aircraft was a Douglas C-47A-35-DL, a military variant of the DC-3, built in 1943.
- 02The crash site was located in Jomala, Åland, approximately 1.5 kilometers from the airport.
- 03Mariehamn Airport had ILS equipment in storage, but land disputes had prevented its installation for two years.
- 04Three people survived: flight attendant Marianne Kullberg and two male passengers.
- 05An unauthorized passenger, WWII ace Ilmari Joensuu, was in the cockpit at the time of the crash.
- 06The wreckage remained in the forest for nearly 55 years until it was removed in 2018 due to environmental concerns.
- 07A memorial stone was erected in 1967 by the Godby Rotary Club, located approximately 200 meters from the crash site.
Safety Actions & Advisories
Weather Minima Revision
The AIB recommended that airlines adopt stricter weather standards than the ICAO Obstruction Clearance Limit (OCL).
Infrastructure Upgrade
The investigation proposed the immediate installation of ILS and Ground-Controlled Approach (GCA) equipment at Finnish airports to replace NDB-only systems.
Known Controversies & Unanswered Questions
Unauthorized Cockpit Occupant
Reference ↗Contemporary press speculated that the presence of former pilot Ilmari Joensuu in the cockpit distracted the crew, though the official report found no evidence to support this.