Flyers should arrive at airports hours in advance and expect slow, confusing security arrangements while the government sorts things out in the wake of a passenger's attempt to light an incendiary device aboard a Northwest flight from Amsterdam to Detroit.

If you're on an international flight into the U.S., you may be forced to stay in your seat for the last hour of the flight. But if you're on a domestic flight, it may be business as usual.

Don't worry if you're confused or if things seem contradictory. Apparently, that's the point.

"These [security] measures are designed to be unpredictable, so passengers should not expect to see the same thing everywhere," Homeland Security secretary Janet Napolitano said in a statement. (Read the secretary's statement here:

Still, though, various governments and airlines have explained at least part of what you're going to have to endure for the rest of the holiday travel season.

What To Expect: At The Airport

At the airport, expect plenty of delays. For domestic flights or flights originating in the U.S., Continental Airlines' website suggests showing up at the airport "one hour prior to normal processing time," which means at least two hours before your flight. "Ninety minutes to two hours is probably not a bad idea," agreed Southwest Airlines spokesman Paul Flaningan.

So far, we haven't heard of any baggage restrictions on domestic flights beyond the usual.

For international flights into the U.S. , the Canadian government advises showing up three hours in advance.

On flights from Canada to the US, every passenger will be subject to a full pat-down twice on their way to the plane, Canadian government officials told the Montreal Gazette.

Passengers should expect "flight delays, cancellations and missed connections," according to Air Canada, so prepare to spend more time at the airport than you originally planned for.

Passengers will also be restricted to one carry-on bag when flying from Canada or from London's Heathrow or Gatwick airports to the U.S. British Airways, Air Canada, and WestJet have waived at least some checked-baggage fees as a result, although U.S. carriers haven't.

Beyond the UK and Canada, it looks like restrictions will vary by country. MSNBC is reporting that passengers are being advised of a second security check, but no new carry-on baggage restrictions in Brussels, and no new restrictions at all in India or Nigeria.

What to Expect: In The Air

If you're traveling on a domestic flight, you probably don't need to worry about new restrictions on carry-on bags or behavior on your flight. Flaningan said that it's business as usual at Southwest, albeit with people being "more vigilant," because they're a domestic-only carrier.

While it's been widely reported that passengers on one New York-Tampa flight were forbidden from leaving their seats or using items in their laps, this doesn't seem to be an actual TSA policy. Flaningan said Southwest, with its domestic flights, "hasn't really been affected" by inflight restrictions.

Other airlines we contacted directed us to the TSA, which said in a statement that "passengers flying from international locations to U.S. destinations" -- presumably, as opposed to folks on domestic flights -- "may notice additional security measures in place."

So it seems the real problems come for folks on inbound international flights into the U.S. According to Air Canada's website and confirmed by independent aviation industry sources, the TSA has mandated that you'll have to remain in your seat during the final hour of each flight, without holding anything in your lap or getting at your carry-on luggage.

That means no laptops, for sure, and it may even mean no books or magazines, though that part remained vague. Prominent blogger Xeni Jardin of said on Twitter that her seatmate was allowed to do a paper Sudoku puzzle on her flight from Latin America to the U.S., though her laptop was nixed.

It's extremely unclear what this means for folks who really need to go to the bathroom or who need to calm a crying child.

For How Long?

A little historical perspective might be useful here. In 2006, a bunch of British terrorists were arrested for trying to blow up planes using liquid explosives. They were arrested on August 9. For four days, the TSA banned all liquids and gels in carry-ons. On August 13th they began allowing medicine and baby food, and the current liquid restrictions went into effect on September 26.

Airline sources agree that the new regulations may be temporary. Canadian airline WestJet says "these new procedures are scheduled to be in effect until at least December 30, 2009," while Italian civil aviation officials told MSNBC that the initial set of regulations would remain in place for 72 hours.

Things should hopefully start to shake out by the first week of January.

What to Do

So what do we advise?

  • If you're flying domestically, arrive at the airport two hours before your flight and be very patient. Print out your boarding pass in advance at home. Expect long, slow lines at security.
  • If you're flying internationally, choose an airline with good in-flight entertainment. If you've already chosen your airline, bring good old analog books for yourself, and small toys and puzzles for children. You have a better chance of being allowed to use those than of being allowed to use anything electronic.
  • Scope out inexpensive airport hotels and make a plan in case your plane is cancelled. Make plans in case you encounter 4-hour, 8-hour, or 24-hour delays. This is always a good idea during the holiday period, but it's an even better idea now.
  • Pack to be searched. Don't just ball everything up and stuff it in your suitcase. Putting things in discrete, zippered compartments or bags helps you reassemble your luggage after the security agent takes it apart.
  • Keep an eye on your airline's website. These regulations may change at any moment.
Read more from Sascha Segan about airplane security via his Twitter account.