Mystery smells caused problems on two separate US Airways flights on Wednesday.
Passengers on Flight 439 from Philadelphia to Las Vegas had to switch aircraft after a persistent odor was detected. The flight, carrying 134 passengers, was delayed nearly six hours, Valerie Wunder, a spokesperson for US Airways, told msnbc.com.
The flight crew detected an odor before takeoff, and the plane returned to the gate, Wunder said. Later, after the jet took flight, the crew noticed the odor once again, and the plane returned to Philadelphia International Airport, where US Airways swapped out the aircraft.
In a separate instance, four flight attendants were transported from Florida’s Fort Lauderdale-Hollywood International Airport to a hospital as a precautionary measure after a smell onboard a US Airways plane made them feel ill, Wunder said.
The odor was caused by the overservicing of the auxiliary power unit, Wunder said. As a precaution, the flight crew called paramedics.
The local fire department opted to call in a hazardous materials team, Wunder said. Readings taken came back negative, according to a report on NBC Miami.
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Joe Myxter has been running msnbc.com's Travel section since 2006. Follow him on Twitter.


"This is your Captain speaking. Okay, who farted?"
But seriously, the odors probably reflect the quality of service I've seen from airlines as of late.
What about the passengers? Only the flight attendants were sent to the hospital as a precautionary check?
Two separate flights?? Kind of misleading since it was the same aircraft.
Not the same aircraft. As for only the flight attendants going to the er, a they are more exposed since the smell is usually localized in the aft of the plane. If a passenger was feeling ill, they would have been taken also.
why fly?