THE model of helicopter that plunged into the roof of the Clutha pub in Glasgow was also involved in a crash in the southeast of England six years ago.

In September 2007, a Eurocopter EC135 T2 crashed east of North Weald Airfield in Essex.

Although the pilot and his wife were unhurt, the aircraft was badly damaged.

An Air Accidents Investigation Branch (AAIB) report into the incident said there had been a disengagement of the autotrim, which is used to maintain the aircraft's position.

This had led the pilot to think he had suffered a total engine failure.

The AAIB recommended Eurocopter review the Stability Augmentation System (SAS) switch system on EC135 helicopters "to reduce the likelihood of inadvertent de-activation of the SAS".

The twin-engined helicopter is part of a family of aircraft that first entered service in 1996. More than 1000 have been built at the Eurocopter plant in Germany and they are widely used by police and ambulance services.

The T2 is a replacement for the T1. In 2002, a T1 crashed in a field in East Ayrshire.

The aircraft, which was giving support to a police operation, was destroyed, but the pilot and the two police officers aboard survived their injuries.

The pilot had encountered snow showers and cloud and had come down during a search of woodland and fields.

Wreckage was strewn over a 50-yard area close to power lines and the farm buildings.

The AAIB report into the crash concluded: "No defects were found with the helicopter or any of its systems, which could account for the behaviour of the helicopter and the loss of control."

A Scottish police helicopter also crashed in 1990, when a Bell Jet 206 came down in bad weather at Eastwood Toll in Glasgow. Sergeant Malcolm Herd was killed when the helicopter struck the side of a block of pensioners' flats and fell to the ground.

An initial bulletin detailing the basic events of the Clutha crash is expected to be issued soon by the AAIB. However, it could be some time before the cause of the accident is known and the body is able to publish a full report.

The investigation team, which is based at Farnborough in Hampshire, will be able to talk to eyewitnesses. Investigators will want to know what those in the vicinity saw and what they heard.

The AAIB will also be keen to study any flight data recording equipment that may have been on the helicopter.

In the August 2013 North Sea helicopter crash, in which four people were killed, the AAIB was able to recover the combined voice and flight data recorder.

This revealed details of the entire flight and of a number of hours of operation before the flight.

Investigators were able to listen to commands given by the captain and the co-pilot as well as passenger announcements.

David Learmount, operations and safety editor at Flight Global, said: "This type of helicopter is sophisticated and robust. It's a very modern aircraft. I think what has happened here is that you have had an aircraft that became either uncontrollable or partially controllable."

"We just don't know how much control the pilot did have in the final seconds of the flight. Something dramatic has probably suddenly occurred - probably some mechanical failure of some kind."

He added: "Helicopters are very mechanically complicated devices. You only have to look at them to see that. Helicopters can, though, glide. This one was a two-engined aircraft. If you lose one engine you can fly on the other one, and if you lose both engines then you can glide."

The British Airline Pilots' Association said it extended its sympathy to everyone affected by the crash. "While there will be understandable questions on why this happened, it is our experience that speculation about causes is often wide of the mark," the body stated. The work of the UK's world-leading Air Accident Investigation Branch will be painstaking and reveal what has happened. From that knowledge we can then, as an industry, look at what needs to happen to reduce the risk of a repeat."

The Eurocopter was leased to the police by Bond Air Services.

A statement on the company's website read: "Bond Air Services can confirm that a police service helicopter was involved in an accident on Friday evening in Glasgow city centre.

"Bond is working with Police Scotland and the emergency services who responded immediately and remain at the scene at the present time. No further details are available at this stage. Our thoughts are with those who have been affected by this tragic incident."