A United Airlines 757 landed safely at Denver International Airport Tuesday afternoon after suffering a bird strike during takeoff.The incident happened on Flight 77 from Denver to San Francisco."We just cleared the edge of the runway and there was a bird that hit the top of the engine," said Gary Little. "Part of the bird went off the top of the engine and part of the bird went into the engine and then the engine went 'errrrrr.""I saw flames shooting out of the engine," said Rebecca Lynn. "Everybody was really calm though. I was surprised."The jet returned to DIA immediately after the incident.United Airlines spokeswoman Megan McCarthy said the bird struck one engine but the plane's other engine wasn't affected. None of the 145 passengers, two pilots and four flight attendants were hurt.Frank Crowe of Chicago, a passenger aboard the United flight, said "there was definitely panic but there wasn't hysteria" after the bird strike."We heard a large thump like we hit something, and the pitch of the engine changed dramatically to the point that it got real quiet, and there was a rattling, wheezing noise," Crowe said.Crowe said the bird hit the right engine.He said after the plane landed and he returned to the concourse, he could see a dent on top of the engine cowling. He said emergency vehicles parked on the tarmac around the plane and mechanics climbed into the engine to inspect it.The strike resulted in an "amber call" at the airport, with fire units responding to the runway in case they were needed.McCarthy did not know if the engine that was hit had stopped operating. She said the pilot's decision to return to the airport was a routine safety precaution.More than 200 wildlife strike incidents happen at DIA each year. The airport spends more than $260,000 a year on its wildlife mitigation program.A US Airways jet splash-landed in New York's Hudson River on Jan. 15 after a collision with a flock of birds knocked out both engines. All 155 aboard survived.Previous to that, there were six reports of birds causing damage to U.S. commercial planes, including a case that occurred in Colorado. In March 2008 an Airbus 318 jet ran into a flock of Canada geese one mile from DIA, causing smoke in the cockpit and damage to its landing gear, engines and nose. The plane landed safely but was moved by a tug to its gate.