Air accident investigators were today continuing to examine the wreckage of a helicopter which crashed in a North Yorkshire field, killing two men.

The cause of the tragedy, at Biggin crossroads, near Sherburn-in-Elmet, remains unclear, although local reports said the helicopter appeared to be in trouble shortly before it hit the ground within yards of a farm.

Both its occupants, a 52-year-old man and his 30-year-old son-in-law, died in-stantly, and locals said it was lucky no-one on the ground had been hurt.

The twisted wreckage of the small two-seater Robinson R22 helicopter has been moved to the Air Accident Investigation Branch's Farnborough headquarters, where it is undergoing a detailed exami-nation.

The crash happened at around 3.30pm on Saturday, as the aircraft was returning to Sherburn Aero Club, from where it had been leased.

Jessie Turner, of Biggin, had seen it moments before as she brought in washing from her garden.

"It had come over low - we are used to that round here - and then there was a hell of a crack," she said.

"I thought at first it had hit something."

Robin Heron, who lives within sight of the scene of the crash, said there were no flames and that he and his wife had initially thought there had been a road accident.

"It's fortunate it didn't come down on the farm," he said.

"It could have been so much worse."

One of the men was thrown clear of the helicopter and an air ambulance was dis-patched to the scene once the alarm was raised.

Senior air accident investigator Philip Gilmartin told the Evening Press that the probe into the cause of the crash could take weeks.

"We will need to look at the aircraft's engineering, its flight controls, history and structure before we can draw any conclu-sions," he said.

"We are still in the very early stages of the investigation."

Sgt Steve Smith, of North Yorkshire police, said both men had been certified dead at the scene and taken to York District Hospital.

They were named as Anthony Baldwin, 52, of Colton, Leeds, and his son-in-law Darren Hunter, 30 of Garforth, who had two young children.

A card on a bunch of flowers left at the scene by relatives said: "I'm sorry I didn't get the chance to say goodbye.

"I love you - I just hope, wherever you are, you know."

A spokesman for Hield's Aviation, owners of the aircraft, said everyone at the com-pany was "shocked and devastated" by the tragedy.

"Our thoughts are with the families of those who died in this terrible accident," he said.

Saturday's fatal accident came just a year and a half after four men died when their light aircraft crashed near Selby shortly after taking off from the same airfield.