Check out this example: SFO-PHL leaving 24 November returning 28 November vs. the same flight to PHL, with a flight to Paris (CDG) on the 28th returning to SFO on 2 December. $2009 just to PHL, or $858 to go all the way to Paris.

Why? Because the fare used between SFO and CDG allows a free stopover in PHL. (Examples are from Expedia.)

Now there's a curious thing about this trip. If you were to plan exactly the same trips using USAirways.com instead of Expedia, it wouldn't get it right. US Airways would present the same price for the simple SFO-PHL round-trip, but would fail to accurately price the Paris trip with the free stopover.

Moral of that anecdote? If you like to use an airline's proprietary site, it still may be useful to get a second or even third opinion for the same itinerary from one of the Big Four (Orbitz, Travelocity, Expedia, Priceline). Or use a bricks-and-mortar travel agent and pay the planning fee if you feel he or she has the necessary expertise.

About Philadelphia. PHL is a convenient jumping off point to other east coast destinations. SEPTA, the regional rail system has frequent and fast service from the airport directly to Amtrak's downtown Philadelphia station. From there by train many cities are a short ride away including New York (1.5 hours or less), Washington, D.C. (about 2 hours), Newark, Baltimore, Wilmington, and elsewhere.

American Airlines - Sacramento to Cabo San Lucas (free stopover in Dallas)

This isn't an example where the fare is actually lower than what you'd pay to get to DFW, but it sure is close. Pay your employer the difference in fare (a whopping $40 in this instance) and enjoy a weekend in Cabo San Lucas, Mexico (SJD). Notice in the second itinerary that it's a nonstop between SJD and SMF - Mexicana flies this nonstop and is a code-share partner of American's. You could also return on an American connection via DFW. (Examples are from aa.com)

Delta Airlines - Sacramento to Buenos Aires (free stopover in Atlanta)

Current fares between Sacramento (SMF) and Atlanta (ATL) on Delta are expensive if you don't plan at least 14 days in advance.

So if a work trip comes up on fairly short notice, why not take a few days of vacation after the business part of the trip and head south - way south - to Buenos Aires (EZE)? Heck, in this case you'll even save your company money.

Here's a round-trip on Delta from SMF to ATL (2-4 December) at $1115.20, followed by an SMF-ATL (2 December), ATL-EZE (4 December), and EZE-SMF (9 December) at $1059.80. Price savings comes to about $45, and you get to practice your tango. (Examples from Delta.com)

Free London stopover on British Airways and free Paris stopover on Air France

British Airways and Air France both allow free stopovers at their respective hub airports in London (LHR - Heathrow) and Paris (CDG - Charles de Gaulle) even on their lowest round-trip fares.

For example, you could buy a ticket from San Francisco to Rome on BA with a break in travel - not just a connection - in London and then continue on to Rome. It would not increase your fare except for some additional tax.

Or buy a ticket from Seattle to Prague on Air France breaking the trip in Paris.

London and Paris are two of the top cities in the world to visit. These free stopover allowances present you the opportunity to visit them in conjunction with another European destination at almost no additional transportation cost.

Some other points about each carrier's stopover provisions:
- Air France actually allows you to stop over in Paris both directions if you wish
- British Airways will allow a second stopover in London for $50
- Air France also allows you to have an open jaw trip plus the Paris stopover(s)
- British Airways allows you the rare privilege of a double open-jaw (flying into and out of different cities in Europe as well as originating and terminating travel in two different U.S. cities

Let's look at an example from British Airways website. In this case, we're really milking all of the rules: San Francisco to London on 21 January. Stopping over for a few days then continuing to Rome on the 24th. Open-jaw (not flying) between Rome and Milan. Flying back from Milan to Los Angeles (double open-jaw) on 3 February.

All of that including taxes and fees for $756.55.

Come back for Airline Fare School # 11 where we'll look at some of the differences between domestic fares and international fares.