Albert Halluin and Judy Perchonock were 70 and 60 years old, respectively, but their relationship was young. They planned to be married in May - three years after they started dating - and spent every weekend at Halluin's mountain home west of Yosemite National Park.

But the Bay Area couple's weekly routine turned tragic Friday night, when Halluin's single-engine plane plummeted into the backyard of a home near Pine Mountain Lake Airport in Groveland (Tuolumne County).

It burst into flames, killing the prominent biotechnology patent lawyer from San Carlos and the energetic Redwood City grandmother.

The crash, which hurt no one on the ground, is under investigation by federal aviation authorities. They said the plane, when it went down at 7:19 p.m., was just an eighth of a mile from the airport.

The incident came just two days after a small plane flying in heavy fog struck power lines and crashed into an East Palo Alto neighborhood, killing all three people onboard and damaging four houses.