The fog on the night of a helicopter crash which killed Tory peer and multi-millionaire Lord Ballyedmond and three others was so thick that RAF rescue crews could not land at the wreckage site, an inquest has heard.
Lord Ballyedmond, also known as Dr Edward Haughey, was killed when the Agusta Westland AW139 came down shortly after take-off near the estate he owned in Gillingham, Norfolk, on March 13 2014.
Dr Haughey's foreman, Declan Small, 42, of Mayobridge, Co Down, Northern Ireland; pilot Captain Carl Dickerson, 36, of Thornton, Lancashire; and co-pilot Captain Lee Hoyle, 45, of Macclesfield, Cheshire, also died.
Flight Lieutenant Ian Smith, an on-call RAF search and rescue pilot at Wattisham airfield, Suffolk, told a jury inquest in Norwich that he was sent to the scene of the crash.
But even with night vision goggles, radar and military training, his helicopter was unable to land because of low visibility, he said.
He added: "It was thick fog, we couldn't see anything below us."
Barry Dolby, who was also working at the house, watched the helicopter take off.
He said: "I could not believe they took off in that fog.
"I've worked on oil rigs and any time there was a sign of fog we would be stuck until it cleared."
The inquest earlier heard Mr Dickerson had warned the helicopter needed to take off "no later than 7pm" because of bad weather.
It did not in fact take off until 7.22pm as Dr Haughey oversaw the hanging of pictures as part of his renovation of Gillingham Hall.
Painter-decorator John Savage, from Newry, Northern Ireland, told the inquest Dr Haughey had been choosing paint colours.
At 7.15pm Mr Hoyle said the helicopter needed to take off immediately or it would be grounded, Mr Savage said.
"His first response was 'John, I'll get back to you about the colours'," Mr Savage added.
He said Dr Haughey immediately left and Mr Hoyle did not seem "stressed or concerned".
Labourer Gary Evans was working near the helipad wh en the aircraft took off. He said by that point the fog had descended.
He added: "I suddenly heard a loud bang, it was so loud it really shocked me.
"It was a cracking sound, like an engine backfiring.
"It was about 10 to 15 seconds after the helicopter started to fly off.
"Afterwards everything was very silent."
Dr Haughey, 70, who lived at Ballyedmond Castle in Co Down, Northern Ireland, was considered to be one of Ireland's richest men, with estimated wealth in excess of £800 million.
Best known as chairman and founder of Norbrook Laboratories, the largest privately owned pharmaceutical company in the world, father-of-three Dr Haughey had a range of other business interests.
A life peer with a seat in the House of Lords, first on behalf of the Ulster Unionist Party before switching to the Conservative Party, he had also previously sat in the upper house of the Republic of Ireland's parliament, the Seanad.
Coroner Jacqueline Lake said the inquest would focus on events leading up to take-off, the training of the pilots particularly when taking off in low visibility, the weather conditions and the regulation of private helicopters.
An Air Accidents Investigation Branch report has already found that the crash may have been triggered by an error in perception along with a lack of training and procedures.
The inquest is expected to last until Friday.
The inquest was shown mobile phone footage of the helicopter taking off captured by one of Dr Haughey's employees.
It showed that conditions were dark and foggy at the time.