Singapore Airlines was forced to cancel a flight bound for London on Monday after a bomb threat but police investigations later found it was a false alarm. Singapore Airlines flight SQ318, due to leave at 9 am (0100 GMT) with 127 passengers, was rescheduled because of the threat. Police conducted a search of the plane at Changi Airport and said the plane was found to be safe. "No bomb was found on the original aircraft," Singapore Airlines said in a statement. The airline said passengers had been transferred to another flight and had departed at 3 pm (0700 GMT) Monday. Singapore Airlines and its unit Silk Air have already installed bullet-proof reinforced cockpit doors and use sky marshals armed with stun guns on flights deemed high risk. Singapore stepped up security after the September 11, 2001, hijack attacks on the United States and tightened it again after last October's devastating bomb blasts on the resort island of Bali in neighboring Indonesia. The last known bomb threat against Singapore Airlines involved a flight bound for Los Angeles in October last year.