ANCHORAGE (Reuters) - Diabetic pilot Douglas Cairns plans a flying expedition to the North Pole to show what those with his illness can accomplish in the air. In most of the world, diabetics are forbidden from flying private planes. Cairns had to give up his British Royal Air Force career when he was diagnosed with diabetes in 1989. Now he is mounting an expedition for the record books. In late April, when daylight and ice conditions are expected to be optimal, he plans to take off from Barrow, Alaska, and fly about 1,300 miles to the North Pole and back. Cairns, who flies a twin-engine Beechcraft Baron, said the journey would make him the first pilot to land a light, twin-engine piston aircraft at the pole, a claim backed up by a spokesman.