When Bonnie Sweeten fled to Florida with her 9-year-old daughter, using the driver's license of a friend to get through airport security, did the airline or document checkers at Philadelphia International Airport drop the ball?

The FBI and the Transportation Security Administration, whose job is checking passengers' government-issued IDs, say no.

Sweeten had a valid Pennsylvania driver's license with a photo that closely resembled her.

"It was a real driver's license, so it had all the security features that a real driver's license has," FBI Special Agent J.J. Klaver said.

The 38-year-old Bucks County woman "was using a driver's license of somebody who looked like her, and the ticket matched the name on the license," Klaver said.

"This country has decided that your driver's license is your primary form of ID," Klaver said. "Driver's license photos, to begin with, are not very good. Pull out your driver's license picture, and hold it up and look in the mirror. How much does it really look like you every day?"

Philadelphia airport officials cooperated with the investigation by providing footage from surveillance cameras. "We knew when she flew, so we pulled the tapes for that time and saw her going through security," Klaver said.

Airport spokeswoman Phyllis VanIstendal said, "On the issue of matching individuals and IDs, the airport is never part of this process either at the ticket counter or the security checkpoints."

TSA spokeswoman Ann Davis said, "Our officers are trained to make sure that passengers' travel documents and government-issued IDs are legitimate."

"They are looking for evidence of tampering" and "proper state markings on the ID. They do look at the photo," Davis said. "However, law enforcement tells us that the woman in question used the valid ID of a coworker with whom she shares a very strong resemblance."

"If the photo bears a strong resemblance to the passenger, and all other markings appear to be legitimate, then the ID would not raise any red flags," Davis said.

Sweeten's daughter did not have to present identification because she is younger than 18.

Sweeten paid cash at the US Airways ticket counter at the airport for two 4:15 p.m. tickets to Orlando.

Airlines track passengers who pay cash or buy one-way fares as part of market research, but such behavior is not considered suspicious or reported to security. "You are allowed to pay cash for an airline ticket," Klaver said.

US Airways said yesterday that it was cooperating in the investigation, but it would not say whether Sweeten had checked a bag or shown ID to the ticket agent. "It's passenger information we just never give out," US Airways spokesman Morgan Durrant said.

"Whether she showed ID to buy an airline ticket, again, she had a driver's license that looked like her," Klaver said. "They don't ask for a second form of ID. We don't use biometrics - fingerprints, retinal scans. It would be prohibitively expensive. We use a driver's license."

"The woman took steps to get away. She was successful at it," Klaver said. "Does this show some systemic weakness in our security process? That's an opinion I'm not going to offer."