A helicopter pilot who was among four people killed in a mid-air collision with an aircraft has been named, as investigators continue to scour the crash site in Buckinghamshire.

Friends and former students have paid tribute to Captain Mike Green, who had more than 30 years of experience.

Mr Green was senior instructor at Helicopter Services, a company based at Wycombe Air Park, and is thought to been on a training flight with a young student when the crash happened near the Waddesdon Estate, Aylesbury, on Friday.

The Cessna 152 light aircraft that collided with the helicopter is also believed to have been on a training flight when the collision took place, killing an instructor and a student reported to be 18-year-old Saavan Mundae, from west London.

Friend Phil Croucher said the death of Mr Green, thought to have been aged in his 60s, was a "sad loss".

The head of training at the Caledonian Advanced Pilot Training Ground School added he believed the crash was an accident and no negligence was involved.

Police and air accident investigators were searching the site close to the estate, which is the former country seat of the Rothschild banking dynasty.

Officials have yet to officially release any details of the victims but police said all four people killed were male. Families of three of the victims visited the crash site on Saturday.

Mr Croucher, 65, who served in the Army with Mr Green, said: "We have lost somebody with a vast amount of experience that could have been passed on to younger people, apart from him being a nice guy generally.

"I used to see him, I popped in on Wednesday when I was passing and had a cup of tea. He was always there before anybody else.

"All of a sudden he's not there. He's gone through no fault of his own and everyone's lost a good friend and mentor."

Helicopter and aircraft in mid-air collision - map locator

Mr Croucher said claims on a pilot forum by an air traffic controller suggested the two had collided accidentally.

The controller said the helicopter had been flying a straight path and the aircraft was descending, meaning pilot would have been unable to see due to "blind spots" below and behind.

"From the available evidence, it's as near to a proper accident as you are likely to see – no negligence, absolutely none," said Mr Croucher.

"That airspace was free airspace," he added, although he admitted the claims were "conjecture".

Superintendent Rebecca Mears of Thames Valley Police said air crash investigators and police were expected to be at the scene until at least Monday.

She said it was "too early to tell" what might have caused the crash.

The collision occurred at 12.06pm and both aircraft, carrying two passengers each, are believed to have come from the Wycombe Air Park about 20 miles away.

Mr Green was a senior instructor with Helicopter Services, based at the airfield.

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A spokesman for the company, which offers training, charter flights and gift experiences, declined to comment.

A former trainee pilot who knew Mr Green described him as "kind and cheerful man".

"I will never forget him sitting by me on my first flights and my exams in three types," he wrote on Facebook. "His loss will be missed by so many military and civilian pilots all over the world and the helicopter industry world-wide has lost a valuable contributor for safety in the helicopter industry."

He added: "Such a kind and cheerful man, with an infectious smile whilst very serious about flying helicopters."

The Cessna 152 involved was built in 1982 and owned by Airways Aero Associations, based at the Wycombe Air Park.

It had flown almost 14,000 hours as of May and had previously suffered substantial damage to its landing gear, propeller and engine following a crash at a Cornish airfield in 1993.

An archived report by the Air Accidents Investigation Branch (AAIB) shows the pilot admitted the 1993 accident was caused by his "misjudgment and lack of experience".

AAIB investigators could be seen carrying what appeared to be wreckage debris in clear plastic bags from the scene of Friday's crash.

Fire investigators and police were also at the site. Police tape marked the inner cordon which could be seen through the thick bushes that surround the area.