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Mr. Castelveter says most carriers maintain links with ground-based medical consultants to help evaluate sick passengers. Flight attendants may ask if there is a doctor onboard, and the CDC may be called in as well.

{bullet} Don’t make jokes about terrorism. “Jokes and/or comments about threats to passengers or the aircraft will be taken seriously,” warns the Transportation Security Administration’s “Summer Travel Tips” brochure.

“It’s important that people not make those inappropriate remarks,” says TSA spokesman Christopher White. “Any behavior, actions or comments that could be construed as a threat to the aircraft or other passengers would merit some kind of security response.”

A woman was detained by authorities in Malaysia after the crew refused to let her children visit the cockpit during a flight and she jokingly said, “My children cannot hijack the plane, but I can.”

{bullet} Know the rules and plan ahead. Go to www.tsa.gov to find detailed information on what is and isn’t permitted in your carry-on.

“As I’m walking up to security, I do a kind of quick mental scan to make sure I’m in compliance,” Miss Gioia says. “Do I have on any jewelry I’m going to need to take off or barrettes in my hair that will make a system go off?”

“When you go through security, treat it like you’ve been pulled over for speeding,” advises Brett Snyder, who writes an online column about air travel at CrankyFlier.com. “Be polite, answer any reasonable questions, and just keep thinking about being done with it so you can move on with your life.”

If you inadvertently bring along a prohibited item, “you can leave the checkpoint area and dispose of it or put it in your checked baggage,” Mr. White says.

Politely acknowledging that you broke the rules by accident can help resolve things quickly. “Don’t believe it’s a matter of these people singling you out because there is something wrong with you,” says Jerry Chandler, travel news blogger for Cheapflights.com.

Mr. Chandler recalls accidentally leaving a Swiss Army knife in his backpack while traveling from Dallas to Birmingham, Ala. “What a boneheaded thing to do,” he says. “They took it over to the checkpoint mailer,” and it was sent back to him without a problem.

A woman was stopped at Ronald Reagan Washington National Airport on June 11 because her toddler’s sippy cup had water in it. She said she was detained improperly and accidentally spilled the water. In response, the TSA posted a video of the incident on its Web site that appears to show the woman turning the cup upside-down and shaking the contents onto the floor.

“The rules are the rules,” Mr. Shankman says. “They don’t make the rules. Screaming at the TSA agent and calling him an idiot is not going to help.”