Searching for airline tickets online can be categorized as followings;

Airline websites

  • Pros: Able to use preferred airlines, concentrate mileage points and take advantage of airline promotions for booking.
  • Cons: Cannot compare with other airlines and have different interface per airline.

Online Airline Booking Sites

  • Example:, …
  • Pros: Able to compare price and schedule of airlines.
  • Cons: Price competition concentrated on simple round trips, hard to compare schedule and have difficulty of price comparison for before and after the searched date.

Price Comparison Sites based on Metasearch engine

  • Example:, …
  • Pros: Able to compare and search both Airlines and Online Airline Booking sites. Capable of regional, seasonal price comparisons via graphic interface.
  • Cons: Due to its limitation of Metasearch engine, it has limited sites to compare and for non-popular routes, it offers impossible airline tickets to book in many cases.

Other than these, Priceline sells airline tickets using a reverse auction system, but it has a small impact. For the reverse auction system of Priceline, I would like to write another post in near future.

In above categories, price comparison sites have shown great advances, but going to skip due to its different nature of existences, let’s move back to the Online Airline Booking Sites.

Operation of Booking Engine

Booking engine of most online airline booking sites is designed like a picture below. When consumers input search conditions, the algorithm come up with a best result considering fares, rules, schedules and seat availabilities synthetically and mark price per schedules. This structure is called Schedule Driven search method. Consumers choose one search result from the listed output of the algorithms.

Booking Engine Algorithm
Algorithm of Booking Engine

Algorithm of Booking Engine: Impossible to draw a correct result and come up with a similar search result instead. It has possibility of existences of better search results.

But there’s a problem. There are too many airports, too many flights, too many fares and even many rules associated with those fares. Like the picture below shows 2,000 paths from San Francisco to Boston with less than 2 stops within the range of US and Southern Canada in a day. If we add few more airports as stops, it will expand to 10,000 paths. Moreover, this document is from 2003. According to [Computational Complexity of Air Travel Planning, Carl de Marcken, Public notes on computational complexity, Fall, 2003], Full Search is impossible for search engine.

San Francisco to Boston: 2,000 paths, source: Computational Complexity of Air Travel Planning, Carl de Marcken
San Francisco to Boston: 2,000 paths, source: Computational Complexity of Air Travel Planning, Carl de Marcken
Complexity of Air Search
Complexity of Air Search, source: Computational Complexity of Air Travel Planning, Carl de Marcken

Multiple Destinations: With expand of segments, operation time increase geometrically. Simplifying many factors eventually lead to poor search results.

Booking Engine Algorithm cannot consider full data, therefore it only offers outcome of certain similarities. Years of technology improvement enables excellent result in simple round trips. However, long distance paths have far more complicated routes and in terms of Multiple Destinations with complex itinerary, many search results are rather not efficient.

A picture below shows a search result for itinerary of ‘Prague-London, London-Hong Kong, Hong Kong-Phuket, Chiang Mai- Bangkok and Bangkok-Budapest’ from Priceline. The cheapest one is $3,303 with multiple stops in each flight, meaning this is not the great schedule. Moreover, Expedia doesn’t show a result for this itinerary.


Priceline Search Input Prague-London-Hong kong-Phuket Chiang Mai-Bangkok-Budapest
Priceline Search Result Prague-London-Hong kong-Phuket Chiang Mai-Bangkok-Budapest

Actually this itinerary can be booked by 1,193,600 KRW ($1,164) according to the picture below. But it is not always possible to book any itineraries with cheap and convenient schedules. Examining airlines’ fare and rule is essential to set one’s itinerary. Since there is no guarantee of successfully reserve a booking class of cheap fare, it can increase its possibility by adjusting one’s itinerary flexibly. Obviously, only a travel agent with broad experience can book such a complex itinerary. But the travel agent hardly ever does this service upon request.

Terminal Search result Prague-London-Hong kong-Phuket Chiang Mai-Bangkok-Budapest

Like I mentioned in previous post about The Nature of Airline Tickets for Smart Airline Booking, able to book multiple Destinations with attractive price is due to the entity of airline tickets.

next post, I will write travel agents could book Multiple Destinations shown above and its process and how come they won’t and couldn’t do this even if upon consumer’s request.

For the record, contrast to the technology introduced above, many airline booking sites in Korea use Fare Driven method to book air tickets. If time allows, I would like to write a post about why Korean airline booking sites choose this particular ways with pros and cons of its system.