It happened at 10:15 a.m. Monday.
US Airways Flight 37 to Los Angeles had 139 passengers onboard.
The plane was on the taxiway when a trailer being towed by a pickup truck broke loose and became wedged under the plane.
The trailer held a 300 gallon plastic tank labeled "jet fuel."
The pilot of flight 37 was waved down by other pilots.
"They're saying that we're dragging some kind of cart under the plane. So I guess we might be here for awhile," the pilot can be heard on the tower tapes.
Action News spoke with one passenger by phone who was clearly shaken up.
He says the plane was close to taking off when it suddenly stopped.
"Then all of a sudden, emergency vehicle after emergency vehicle kept coming up," the passenger said.
Later, the pilot had a better picture of what was under his plane.
"There's some kind of a fuel cart that rolled and hit the airplane. Because there's some kind of fuel involved, we're contemplating possibly deplaning the passengers here," the pilot said.
Emergency responders eventually determined the tank was full of water that had been siphoned from fuel tanks.
With no danger of explosion, the plane returned to the terminal and the airline scrambled to find new flights for the passengers.
The plane was taken out of service to repair damage to a wheel and the landing gear door.
Passengers were not happy.
"I don't understand how you can miss it. I was just angry at that point that something like that can happen," the passenger told Action News.
The company operating the trailer that got loose is Skytanking USA.
Action News tried to get comment from their Philadelphia office, but the manager says they're not allowed to speak on the matter.
US Airways says that all but 20 passengers traveled on to California. The 20 are staying at a local hotel and will be traveling to California tomorrow morning.
Multiple agencies are now investigating.
The Federal Aviation Administration (FAA) released the following statement about the incident Monday afternoon:
At 10:15 am today, US Airways Flight 37, an Airbus A320 aircraft, was taxiing out for departure when its right main gear was struck by a fuel cart at Philadelphia International Airport. The fuel cart broke loose from the vehicle towing it. When the US Airways flight crew saw the cart coming toward the aircraft they immediately stopped and shut down the right engine. An aircraft tire was damaged.