Cape Air, which provides commuter service to Portland, Augusta and Rockland, has signed a letter of intent to purchase 75 fully-electric airplanes from Eviation Aircraft.The Eviation Alice can carry nine passengers and two crew. It has a range of about 500 miles on a charge with a top cruising speed of nearly 300 miles per hour."Together with Eviation, we are creating the next generation of air travel, in which electric flight will be the industry standard," said Cape Air board chairman Dan Wolf."Cape Air remains committed to sustainability, growth and innovation," said Cape Air president and CEO Linda Markham. "Our communities will benefit from emission-free travel."It was not clear when the planes would be in service.