TALLINN - A commission set up to investigate last month's helicopter crash that took 14 lives has ruled out a defective rotor blade and engine failure as the causes of the accident.
The commission has so far failed to establish why the chopper crashed.
"We've a fairly true picture of how everything happened, but unfortunately we're unable to say why it happened," chairman of the Economy and Communications Ministry commission, Taivo Kivistik, told reporters on Sept. 13.
Commission deputy Tonu Ader said the commission has ruled out several earlier theories about possible causes of the accident, but he declined to say which versions investigators considered the more likely.
However, Ader did say the probe was unable to establish whether some parts of the helicopter, which was owned by the Finnish Copterline company, broke off in the air.
The parts that did separate from the chopper were lying near the wreck on the bottom of the sea, suggesting they broke on impact with the water, and the only part lying farther away from the wreck was a blade of the main rotor.
"The commission has serious grounds to eliminate the breaking off of the main rotor blade as a cause of the crash," Ader said.
He said the commission concluded that the blade found at a distance from the wreck did not break off until the helicopter hit water. He made it clear that all four blades had broken off and had sustained relatively similar damage.
The commission also ruled out the possibility of the engines failing during flight. Ader said the engines continued working till almost the moment the helicopter struck water.
As he explained, the helicopter started behaving inexplicably around 37 seconds before plunging into sea. First its nose lifted up while the helicopter itself started to turn to its left side and away from its original course. Then it turned back right and started falling, making 13 full turns to the right 's or one turn in 2.5 seconds on average 's until it hit water.
"The high speed of turning may indicate an overload that prevented the crew from getting control of the helicopter," Ader said.
He said the tape of the discussion between the pilot and co-pilot showed that right before the moment when things started to go wrong, the pilot said, "Let's boost power." This was followed by an expression of surprise and, a few seconds later, by a very quiet Mayday call repeated three times.
A bit later the co-pilot's question, "Have we lost the tail?" could be heard following which the recording contained no distinguishable phrases.
According to Ader, clear evidence exists that the helicopter's tail rotor continued turning until the chopper hit water and that the aircraft's hydraulic systems were in order.
The Sikorsky S-76 C+ helicopter plunged into the Baltic Sea on Aug. 10 shortly after taking off from Tallinn for Helsinki, claiming all 12 passengers and two pilots on board.
Families of the victims withdrew their petition not to make public the interim report of the investigation commission on Sept. 13.
"We've dropped the petition," barrister Leon Glikman from the Teder, Glikman & Partners law firm representing victims' families told the Baltic News Service. "The reason is that the report does not contain privacy-invading personal data, it does not touch our client's interests."
The investigating commission was supposed to publish its interim report the same day but did not do so because of the families' petition.
The commission is to complete its final report within a year of the accident, or by Aug. 10, 2006 at the latest.