A spokesman for the Federal Aviation Administration says the US Airways flight 432, a Boeing 757, landed in San Francisco a little after 5 p.m. Friday.
An airport spokesman says the plane landed "uneventfully" and taxied to the gate. There were reports that there was smoke inside the cockpit. No injuries were reported.
US Airways says the flight was carrying 175 passengers and six crewmembers.
A spokesman for the airline says the emergency was declared as a precaution.
The diverted passengers were to be put on another US Airways flight for their delayed trip to Hawaii.