The mystery of why an aeroplane plunged into the sea off Kent remains unsolved - despite its last moments in the air being revealed.

Investigators have been unable to find out why the light aircraft slammed into the water off Dungeness.

The crash last year had prompted a major international rescue bid involving Dungeness RNLI.

But now a report by the Air Accidents Investigation Branch said: "The investigation did not determine the cause of the accident."

Pilot Sascha Schornstein's plane plunged into the sea, smashing into pieces, last July 21. Wreckage was discovered 15 miles south of Dungeness Point.

The plane, going from Blackbushe Airport in Hampshire to Le Touquet, vanished from radar just before it plunged.

Mr Schornstein, who was alone, made no distress call and had not baled out in a parachute.

To this day, the 26-year-old not been found - dead or alive.

The Air Accidents Investigation Branch's bulletin said: "The lack of evidence that the pilot used the emergency parachute system and absence of any emergency radio transmissions means that pilot incapacitation could not be discounted as a factor."

It added investigators examining wreckage concluded the plane had slammed violently into the sea as it was found in several pieces. The propeller had still been turning at the point of impact.

The report said weather had affected visibility over the Channel, with haze and low cloud or fog with little or no discernible horizon.

It said the Cirrus SR22 plane, registered N147KA, took off from Blackbushe at 9.14am.

It added Mr Schornstein had himself expressed concern about the poor visibility, so he flew seven brief test circuits before he was satisfied he could make the full journey.

Witnesses said he seemed alert and in good spirits before he took off.

His last message to ground control was at 10.20am, saying his was crossing the coast east of Seaford, East Sussex, and gave an estimated time of arrival at Le Touquet of 10.44am.

Radar then tracked him as going over the sea at Beachy Head, a few miles east of Seaford.

The plane disappeared from radar at 10.34am and French authorities put out an alert when he failed to land in Le Touquet.

The last four minutes of radar trackings had show the plane moving more erratically, changing speeds and altitudes and zig-zagging its course.

Its speed went from a steady 140 knots, spiked to nearly 180 and fell to just over 100 in its last couple of minutes.

Altitude also almost halved from just under 2,000ft to just over 1,000ft.

Despite, up to that point, going in a straight line over the English Channel, it also turned left and right before heading towards Boulogne, 24 miles from the destination of Le Touquet. Then it could no longer be traced.

Search and rescue teams found wreckage in the area of the last radar trackings.

Parts of the plane brought back by Pride and Spirit included both main cabin doors, sections of the fuselage and pieces from both wings.

Mr Schornstein's flight bag, rucksack and logbook were also recovered.

A life raft was also found torn from its cover bag but not inflated.

Lifeboat crew members who came across the wreckage also reported a strong smell of fuel in the area.

An examination of the wreckage showed the American-registered plane had been maintained according to regulations and a pilot who had flown it the day before the crash had said that it was working normally.

German national Mr Schornstein was married and lived in London.