No technical malfunction which might account for the helicopter crash which killed Tory peer Lord Ballyedmond and three others has been identified to date, air accident investigators said today.
Dense fog had developed on the night of March 13 when the AgustaWestland AW139 helicopter crashed near Gillingham Hall in Norfolk, a special bulletin from the Air Accidents Investigation Branch (AAIB) said.
The bulletin concluded: "AAIB investigation to date has not identified any technical malfunction which might account for the accident.
"The investigation continues, with the aim of identifying any technical matters of relevance, as well as focusing on flight in degraded visual environments."
The report said the helicopter had been scheduled to leave Gillingham Hall for Coventry Airport at 6.30pm but the passengers had not been ready to depart until around 7.20pm.
The report went on: "By this time, night had fallen and dense fog had developed; witnesses described visibility in the order of tens of metres."
The pilots were captain Carl Dickerson, 36, and co-pilot Lee Hoyle, while Lord Ballyedmond, 70, who was Northern Ireland's richest man and Declan Small, who worked for the peer, were the passengers.
Today's report said the helicopter lifted into a hover at 7.24pm and then hover-taxied to the middle of the paddock in which the helipad was sited. The captain, who was the pilot flying, briefed that he would climb vertically from the hover before setting course.
The report said that the aircraft climbed initially with very little ground speed. At an altitude of around 32ft the helicopter picked up forward speed and continued to climb, with altitude peaking at 125ft above ground level (agl) and speed increasing through 60 knots (just over 69mph).
The report continued: "The helicopter thereafter pitched progressively nose-down, entering a descent as it did so, reaching 35 degrees nose-down one second before the end of the data recording.
"The final complete frame of the recorded data analysed to date showed a pitch altitude of 25 degrees nose-down, a radio altitude of 82ft agl and a ground speed of 90 knots (just over 103mph). The recorded rate of descent was 2,400ft per minute and increasing."
The AAIB said that in the final seconds of the flight the co-pilot made two verbal prompts to the captain regarding the aircraft's pitch attitude. Simultaneously, the recorded data showed that "full collective" - a full adjustment to the rotor blades' pitch angle - was applied.
The report said the recorded data includes information relating to cautions, warnings and faults. The report went on: "None were active during the accident flight with the exception of the last data points when full collective had been applied and a gearbox torque-related caution was triggered."
The report said the aircraft struck the ground in a gently rising field immediately ahead of a row of rolled hay bales about 420 metres from the take-off point. There was no evidence that the helicopter had made contact with any other object prior to this point.
Distribution of the wreckage indicated that, immediately after the main rotor blades struck the ground, the helicopter became airborne again and rotated clockwise before striking the ground 148ft (45m) beyond the first mark.
It came to rest upright 207ft (63m) from the initial impact point.
Initial examination confirmed that both engines had been operating during the impact sequence and that the rotor head could turn freely.
Impact damage had resulted in the failure of the tail rotor drive shaft and the base of the fin, but witness marks confirmed that the drive shaft had been rotating during the impact sequence.
The AAIB added that the tail rotor drive shaft was also found to rotate freely when the main rotor head was turned.
As well as getting information from the cockpit voice and flight data recorders from the helicopter, the AAIB said they had also studied a video recording of the helicopter's departure and gathered information from eye witnesses.
"The investigation is ongoing and a final report will be published in due course," the AAIB said.