A backpack on fire almost got tossed onto a US Airways flight at Phoenix Sky Harbor International Airport on Tuesday, but a baggage handler saw the smoke and patted it out.

Flight 200, a 10 a.m. departure to San Antonio, had already boarded about 50 of its 108 passengers at Terminal 4 when the baggage handler grabbed the red backpack that was described as "unusually hot" and "smoking," said Lt. Rick Gehlbach of the Phoenix police airport bureau.

"It could have been very dangerous if it would have gotten into the cargo area of the plane," Gehlbach said.

A puff of smoke and flames arose from the bag when the baggage handler grabbed it. The handler patted out the fire and removed the backpack before it reached the plane, which was carrying 40,000 gallons of jet fuel, police said.

The Phoenix Fire Department's hazardous material team as well as the bomb squad checked out the backpack, Gehlbach said.

Authorities believe that toiletries and friction were the cause of the unusual incident.

After seeing wear marks on the bag, airport police theorized that the backpack got stuck on the landing belt between two larger bags.

The continuous movement of the belt heated up the bag. The heat, in combination with chemicals that were released from broken toiletries in the backpack, could have caused the fire.

"In essence, it was somewhat of a freak accident," Gehlbach said.

Authorities evacuated about 130 people out of gate A-17, including the 50 passengers on board and ramp personnel.

US Airways had moved the plane away from the terminal as a precaution, Gehlbach said.

Passengers, including the owner of the backpack, were reboarded on the same plane and took off at 11:15 a.m. Authorities returned the remains of the backpack to the owner with her belongings bagged up.

Police questioned the owner of the backpack, who seemed "perplexed" and didn't understand how her bag could have created a problem, Gehlbach said. The woman had come from a connecting flight where her bag had likely already been screened at a different airport.

The security incident comes a week before the start of what is traditionally the biggest travel season of the year. As many as 150,000 people pass through Phoenix Sky Harbor's gates each day during the Thanksgiving weekend.