Three San Mateo and Burlingame people were killed instantly Sunday when their light plane crashed near Hayward Airport just after radioing for permission to make an emergency landing. Killed in the crash were pilot Brian Herrmann, 24, 820 N. Delaware St., San Mateo; his fiancee, Roberta Jean Limbert, 21, 625 Rand St., San Mateo; and her mother, Mrs. Margaret Hazel Limbert, 60, 1145 El Camino Real, Burlingame. The Alameda County Coro- ner's Office said the three died in a 1957 Beechcraft Bonanza, a 240-horsepower four-place low-wing plane based at San Carlos Airport and owned by David Lampert of Woodside. Mrs. Limbert and her daughter were employes of the Turek Frozen Foods Co. of Burlingame. They were reportedly on their way to Stockton to see Mrs. Limbert's sister when the plane went down. Witnesses told the Almeda Countv coroner that Federal Aviation Administration officials said the plane crashed about two miles southeast of the air- port, apparently because of engine failure.