A plane performing an aerobatic display nosedived towards the ground and nearly crashed after a loose pen in the cockpit jammed the controls, an investigation has found.

The vintage single-engine 'Chipmunk' aircraft was performing an aileron roll at 600 feet when the controls stopped working properly and it plummeted to just 50 feet above the ground.

Only by vigorously pushing the pedals in the cockpit was 49-year-old pilot Paul Green able to regain control of the plane and perform an emergency landing.

A report into the incident, which took place last September close to White Waltham Airfield in Berkshire, England, has concluded that a partially crushed pen found in the fuselage had probably become lodged in the rudder control circuit, causing the 65-year-old DHC-1 Chipmunk 22 to plunge towards the ground.

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The Air Accident Investigation Branch said: "During an aerobatic display the aircraft failed to respond to the pilot's control inputs due to a restriction in the rudder control circuit caused by a loose article.

"The pilot reduced power and declared a MAYDAY.

"A detailed inspection of the aircraft completed a few days after the event confirmed that there were no defects with the flying controls. However, a partially crushed pen was found within the fuselage.

"The damage to the pen indicated that it was the probable cause of the control restriction.

"The pilot reported that, prior to the incident flight, a pen top had been recovered from the rear cockpit of the aircraft during the pre-flight loose article check but no other articles had been seen."

As a result of the incident, the pilot has introduced more rigorous pre- and post-flight inspections of the aircraft for loose articles and only allows pens to be carried if they are securely tied to the pilot's or student's flying suit.