A TIMES INVESTIGATION / CALIFORNIA'S VULNERABLE 911 SYSTEM - In California, a cellphone call to 911 can be hit or miss

Susana Tupou was frantic as she raced across the street toward a neighbor mowing his lawn. Moments before, the 16-year-old had discovered her mother face-down on the living room carpet.

The neighbor, Antonio Zamora grabbed his cellphone -- the only phone he had -- from his belt clip and punched in 911.

The global positioning system linked to Zamora's phone should have sent information to California Highway Patrol dispatchers, showing his location in a subdivision of two-story homes in the northeast part of the city.

But on this day last fall, the CHP's screen came up blank.

As the minutes ticked by -- with Susana wailing in the background, "What can we do? . . . What can we do?" -- Zamora struggled to make one operator, then another, understand just where the emergency was.

The ordeal bared critical vulnerabilities in California's 911 system. Had Zamora used a land line phone, his address would have popped up automatically on dispatchers' computers. Instead, by using a wireless phone, he was depending on less reliable tracking technology.

Despite technological advances and reform efforts over the last decade, the automated system often fails to determine the location of cellphone callers. A Times review of data for August and September, the only months for which numbers are available, found that more than 1 in 5 911 wireless calls in California -- more than 300,000 in all -- came into CHP dispatch centers with no location information.

Hundreds of thousands of additional calls arrived with limited or imprecise information.

Under federal regulations, dispatch centers in California that accept wireless calls are supposed to receive, at a minimum, the address of the antenna transmitting the call -- a rough indication of the caller's location, officials said. In areas like Susana's neighborhood, served by call centers with advanced technology, a dispatcher should be able in nearly all cases to plot locations within a maximum of 980 feet.

"This is critically important to public safety and critically important to people -- to be able to pick up the phone and have the local police or local fire department find you," said Kevin J. Martin, chairman of the Federal Communications Commission.

The FCC released an order Tuesday to tighten cellphone tracking standards for 911 calls over the next five years, highlighting national concerns over finding wireless users in emergencies.