Mystery over Lancashire crash helicopter's mayday call
Investigators have been unable to establish why a mayday call was made from a helicopter before it crashed in Lancashire, killing two people.
Instructor Steven Lewis, 38, made a mayday call 20 minutes into the training flight from Blackpool Airport.
But although the transmission mentioned "failure", Mr Lewis, from Merseyside, sounded calm, said a report by the Air Accidents Investigations Branch (AAIB).
It said the most likely cause of the crash last year was loss of control.
The Schweizer 269C crashed shortly after sending the mayday signal as it flew over Poulton-le-Fylde at about 1210 BST on 22 September 2009.
Blackpool control tower requested a further transmission, which consisted mainly of background noise, the report said.
"Transmission of the mayday indicates that the instructor had identified an emergency situation and, although it was not possible to determine what this was, the mayday itself was delivered in a voice that, according to family members, sounded calm and held no sense of panic," the report said.
"Analysis of the final transmission, however, suggests that the helicopter was by then no longer in controlled flight."
The AAIB said examination of the helicopter, which crashed on the east bank of the River Wyre, near Stalmine, revealed that the main rotor was turning at low speed on impact, "but the reason for this could not be established".
The AAIB said the most likely cause of the accident was "a loss of control during an attempted forced landing downwind".
Mr Lewis, from Rainhill, had been instructing student Philip Charles Gray, 45, of Mawdesley, near Chorley, Lancashire.
In a statement released shortly after the crash, Mr Lewis's family said he "loved to fly".