The mysterious severance of a wind turbine blade may have been caused by a mechanical failure, an expert said today.
The 213ft turbine at Conisholme in Lincolnshire was left wrecked by the incident, which saw one blade completely severed and another one damaged.
Local residents reported seeing a bright light on the morning it happened, prompting speculation that a UFO had caused the damage.
But Fraser McLachlan, chief executive of GCube, which insures more than 25,000 wind turbines worldwide, said that although it is unusual, this type of incident happens about five or six times a year.
"It does happen that a blade will sometimes just come off a machine for one reason or another," he said. "The main reason is the blade may shear.
"We don't normally see things like aircraft - or UFOs - hitting them. It's usually a mechanical failure that causes the blade to separate from the main hub."
The freezing weather was another possible cause of the breakage, he said, adding that it could cost up to £250,000 to repair.
Others believed there could be more to the incident than a technical fault.
Robert Palmer, 66, leader of East Lindsey District Council and member of Lincolnshire County Council, wants both authorities to investigate what happened.
The turkey farmer from North Somercotes said he saw a bright white light with an orange edge as he drove close to the turbine on Sunday morning.
He said: "I would be very interested to find out what it was. If we are being looked at by other people, by other planets, it would be interesting to find out why they have chosen this part of the country.
"I am not counting it out that it was a UFO."
Russell Kellett of the Flying Saucer Bureau said this was the latest of a number of sightings of strange lights in the north of England reported to him since New Year's Day.
"I've been inundated," he said. "A local witness told me they had seen what looked like an orangey light in the area near the wind turbine and early on Sunday morning they heard a loud bang.
"There's no doubt something hit it."
Wind turbine company Ecotricity said it had never seen anything like this.
A spokeswoman said: "We're conducting a thorough investigation into what happened.
"This kind of thing has never happened to us before."
The 72ft severed blade was found on the ground beneath the turbine, she said, adding that the company could not speculate on the cause of the damage.
"An engineer has been on the site since it happened, early on Sunday morning, and is carrying out a sort of forensic investigation."
A spokeswoman at nearby RAF Scampton, where the Red Arrows are based, said they did not have any flights at the weekend.
She said: "I am not an expert in flight so I am not in a position to speak with any authority.
"I don't think you could end up with any sort of aircraft hitting a wind turbine and coming off particularly favourably."
The Ministry of Defence said it was not looking into the incident.
A spokesman said: "The MoD examines reports solely to establish whether UK airspace may have been compromised by hostile or unauthorised military activity.
"Unless there's evidence of a potential threat, there's no attempt to identify the nature of each sighting reported."
Ecotricity managing director Dale Vince said the turbine would be up and running again by next week.