GREENVILLE, Maine (AP) Flags are at half-staff in the Canadian town where a pilot, his wife and daughter lived before a fatal airplane crash in Maine.

The pilot, Joe Robertson, and his wife, Anita, were major philanthropists in southern Ontario after he sold a dental supply firm.

The couple from Niagara-on-the-Lake and their 24-year-old daughter, Laura, were killed Monday when his twin-engine plane crashed in Greenville, Maine. They were headed to a vacation on Prince Edward Island.

The cause of the crash remains unknown.

The National Transportation Safety Agency reported that Joe Robertson alerted air traffic controllers about losing power. But there have been no conclusions, and the investigation is continuing.